Preclinical Efficacy of a Trivalent Human FcγRI-Targeted Adjuvant-Free Subunit Mucosal Vaccine against Pulmonary Pneumococcal Infection

Lack of safe and effective mucosal adjuvants has severely hampered the development of mucosal subunit vaccines. In this regard, we have previously shown that immunogenicity of vaccine antigens can be improved by targeting the antigens to the antigen-presenting cells. Specifically, groups of mice immunized intranasally with a fusion protein (Bivalent-FP) containing a fragment of pneumococcal-surface-protein-A (PspA) as antigen and a single-chain bivalent antibody raised against the anti-human Fc-gamma-receptor-I (hFcγRI) elicited protective immunity to pulmonary Streptococcus pneumoniae infection. In order to further enhance the immunogenicity, an additional hFcγRI-binding moiety of the single chain antibody was incorporated. The modified vaccine (Trivalent-FP) induced significantly improved protection against lethal pulmonary S. pneumoniae challenge compared to Bivalent-FP. In addition, the modified vaccine exhibited over 85% protection with only two immunizations. Trivalent-FP also induced S. pneumoniae-specific systemic and mucosal antibodies. Moreover, Trivalent-FP also induced IL-17- and IL-22-producing CD4⁺ T cells. Furthermore, it was found that the hFcγRI facilitated uptake and presentation of Trivalent-FP. In addition, Trivalent-FP also induced IL-1α, MIP-1α, and TNF-α; modulated recruitment of dendritic cells and macrophages; and induced CD80/86 and MHC-II expression on antigen presenting cells.

Fcγ receptors and toll-like receptor 9 synergize to drive immune complex-induced dendritic cell maturation

Previous in vivo studies established that inactivated Francisella tularensis immune complexes (mAb-iFt) are a more protective vaccine against lethal tularemia than iFt alone. Subsequent in vitro studies revealed enhanced DC maturation marker expression with mAb-iFt stimulation. The goal of this study was to determine the mechanism of enhanced DC maturation. Multiparameter analysis of surface marker expression and cytokine secretion demonstrates a requirement for FcγR signaling in enhanced DC maturation. MyD88 was also found to be essential for heightened DC maturation, implicating MyD88-dependent TLRs in DC maturation. Upon further study, we discovered that TLRs 2 & 4 drive cytokine secretion, but surprisingly TLR9 is required for DC maturation marker upregulation. These studies reveal a separation of DC cytokine and maturation marker induction pathways and demonstrate that FcγR-TLR/MyD88 synergy underlies the enhanced dendritic cell maturation in response to the mAb-iFt vaccine.

Antigen Presenting Cell Targetted, Adjuvant free Mucosal Vaccine Induces Protection against Pneumococcal Infection

Protein-based subunit vaccines require adjuvants to increase their immunogenicity. However, there is lack of FDA-approved mucosal adjuvant. We have previously shown that targeting antigens to antigen presenting cells increases their immunogenicity. Specifically, Streptococcus pneumoniae (Sp) protective antigen (PspA) fused to a single-chain bivalent-anti human Fc-gamma-receptor-I (hFcgRI) antibody, when introduced into mice, generates protection against Sp. To further enhance the immunogenicity of the anti-hFcgRI-PspA fusion protein, we have incorporated an additional hFcgRI-binding moiety, with the resultant trivalent-anti-hFcgRI inducing better protection compared to the bivalent anti-hFcgRI-based vaccine. This improved vaccine requires fewer immunizations to confer over 90% protection, significantly higher than that of bivalent-anti-hFcgRI-PspA (less than 60%). The trivalent- anti-hFcgRI-PspA also induces significantly higher levels of Sp-specific antibodies. In addition, we observed elevated levels of mucosal IgA responses in trivalent-anti-hFcgRI-PspA-immunized mice compared to that of bivalent anti-hFcgRI-PspA. Both trivalent-anti-hFcgRI-PspA and bivalent anti-hFcgRI-PspA enhanced antigen presentation in FcgRI-dependent manner. We have further observed that trivalent-anti-hFcgRI-PspA induces recruitment of innate immune cells in the nasopharyngeal lymphoid tissue upon intranasal immunization, which is a hallmark of adjuvant activity. Thus, our study suggests that anti-hFcgRI-PspA compensates for the lack of adjuvant by inducing adjuvant effects, and can be utilized as a mucosal vaccine platform.

Evaluation of an outbred mouse model for Francisella tularensis vaccine development and testing

Francisella tularensis (Ft) is a biothreat agent for which there is no FDA-approved human vaccine. Currently, there are substantial efforts underway to develop both vaccines and the tools to assess these vaccines. Tularemia laboratory research has historically relied primarily upon a small number of inbred mouse strains, but the utility of such findings to outbred animals may be limited. Specifically, C57BL/6 mice are more susceptible than BALB/c mice to Ft infection and less easily protected against challenge with highly virulent type A Ft. Thus, depending on the inbred mouse strain used, one could be misled as to which immunogen(s)/vaccine will ultimately be effective in an outbred human population. Accordingly, we evaluated an outbred Swiss Webster (SW) mouse model in direct comparison to a well-established, inbred C57BL/6 mouse model. Mucosal vaccination with the live, attenuated Ft LVS superoxide dismutase (sodB) mutant demonstrated significantly higher protection in outbred SW mice compared to inbred C57BL/6 mice against Ft SchuS4 respiratory challenge. The protection observed in vaccinated outbred mice correlated with lower bacterial density, reduced tissue inflammation, and reduced levels of pro-inflammatory cytokine production. This protection was CD4⁺ and CD8⁺ T cell-dependent and characterized by lower titers of serum antibody (Ab) that qualitatively differed from vaccinated inbred mice. Enhanced protection of vaccinated outbred mice correlated with early and robust production of IFN-γ and IL-17A. Neutralizing Ab administered at the time of challenge revealed that IFN-γ was central to this protection, while IL-17A neutralization did not alter bacterial burden or survival. The present study demonstrates the utility of the outbred mouse as an alternative vaccination model for testing tularemia vaccines. Given the limited MHC repertoire in inbred mice, this outbred model is more analogous to the human in terms of immunological diversity.

Differential In Vitro Cultivation of Francisella tularensis Influences Live Vaccine Protective Efficacy by Altering the Immune Response

Francisella tularensis (Ft) is a biothreat agent for which there is no FDA-approved human vaccine. Currently, there are substantial efforts underway to develop both vaccines and improved tools to assess these vaccines. Ft expresses distinct sets of antigens (Ags) in vivo as compared to those expressed in vitro. Importantly, Ft grown in brain-heart infusion medium (BHIM) more closely mimics the antigenic profile of macrophage-grown Ft when compared to Mueller-Hinton medium (MHM)-grown Ft. Thus, we predicted that when used as a live vaccine BHIM-grown Ft (BHIM-Ft) would provide better protection, as compared to MHM-Ft. We first determined if there was a difference in growth kinetics between BHIM and MHM-Ft. We found that BHIM-Ft exhibited an initial growth advantage ex vivo that manifests as slightly hastened intracellular replication as compared to MHM-Ft. We also observed that BHIM-Ft exhibited an initial growth advantage in vivo represented by rapid bacterial expansion and systemic dissemination associated with a slightly shorter mean survival time of naive animals. Next, using two distinct strains of Ft LVS (WT and sodB), we observed that mice vaccinated with live BHIM-Ft LVS exhibited significantly better protection against Ft SchuS4 respiratory challenge compared to MHM-Ft-immunized mice. This enhanced protection correlated with lower bacterial burden, reduced tissue inflammation, and reduced pro-inflammatory cytokine production late in infection. Splenocytes from BHIM-Ft sodB-immunized mice contained more CD4⁺, effector, memory T-cells, and were more effective at limiting intracellular replication of Ft LVS in vitro. Concurrent with enhanced killing of Ft LVS, BHIM-Ft sodB-immune splenocytes produced significantly higher levels of IFN-γ and IL-17A cytokines than their MHM-Ft sodB-immunized counterparts indicating development of a more effective T cell memory response when immunizing mice with BHIM-Ft.

Differential Growth of Francisella tularensis, Which Alters Expression of Virulence Factors, Dominant Antigens, and Surface-Carbohydrate Synthases, Governs the Apparent Virulence of Ft SchuS4 to Immunized Animals

The gram-negative bacterium Francisella tularensis (Ft) is both a potential biological weapon and a naturally occurring microbe that survives in arthropods, fresh water amoeba, and mammals with distinct phenotypes in various environments. Previously, we used a number of measurements to characterize Ft grown in Brain-Heart Infusion (BHI) broth as (1) more similar to infection-derived bacteria, and (2) slightly more virulent in naïve animals, compared to Ft grown in Mueller Hinton Broth (MHB). In these studies we observed that the free amino acids in MHB repress expression of select Ft virulence factors by an unknown mechanism. Here, we tested the hypotheses that Ft grown in BHI (BHI-Ft) accurately displays a full protein composition more similar to that reported for infection-derived Ft and that this similarity would make BHI-Ft more susceptible to pre-existing, vaccine-induced immunity than MHB-Ft. We performed comprehensive proteomic analysis of Ft grown in MHB, BHI, and BHI supplemented with casamino acids (BCA) and compared our findings to published “omics” data derived from Ft grown in vivo. Based on the abundance of ~1,000 proteins, the fingerprint of BHI-Ft is one of nutrient-deprived bacteria that—through induction of a stringent-starvation-like response—have induced the FevR regulon for expression of the bacterium's virulence factors, immuno-dominant antigens, and surface-carbohydrate synthases. To test the notion that increased abundance of dominant antigens expressed by BHI-Ft would render these bacteria more susceptible to pre-existing, vaccine-induced immunity, we employed a battery of LVS-vaccination and S4-challenge protocols using MHB- and BHI-grown Ft S4. Contrary to our hypothesis, these experiments reveal that LVS-immunization provides a barrier to infection that is significantly more effective against an MHB-S4 challenge than a BHI-S4 challenge. The differences in apparent virulence to immunized mice are profoundly greater than those observed with primary infection of naïve mice. Our findings suggest that tularemia vaccination studies should be critically evaluated in regard to the growth conditions of the challenge agent.

Ex vivo antigen-pulsed PBMCs generate potent and long lasting immunity to infection when administered as a vaccine

Numerous studies have demonstrated that administration of antigen (Ag)-pulsed dendritic cells (DCs) is an effective strategy for enhancing immunity to tumors and infectious disease organisms. However, the generation and/or isolation of DCs can require substantial time and expense. Therefore, using inactivated F. tularensis (iFt) Ag as a model immunogen, we first sought to determine if DCs could be replaced with peripheral blood mononuclear cells (PBMCs) during the ex-vivo pulse phase and still provide protection against Ft infection. Follow up studies were then conducted using the S. pneumoniae (Sp) vaccine Prevnar ®13 as the Ag in the pulse phase followed by immunization and Sp challenge. In both cases, we demonstrate that PBMCs can be used in place of DCs when pulsing with iFt and/or Prevnar ®13 ex vivo and re-administering the Ag-pulsed PBMCs as a vaccine. In addition, utilization of the i.n. route for Ag-pulsed PBMC administration is superior to use of the i.v. route in the case of Sp immunization, as well as when compared to direct injection of Prevnar ®13 vaccine i.m. or i.n. Furthermore, this PBMC-based vaccine strategy provides a more marked and enduring protective immune response and is also capable of serving as a multi-organism vaccine platform. The potential for this ex-vivo vaccine strategy to provide a simpler, less time consuming, and less expensive approach to DC-based vaccines and vaccination in general is also discussed.

Differential Cultivation of Francisella tularensis Induces Changes in the Immune Response to and Protective Efficacy of Whole Cell-Based Inactivated Vaccines

Francisella tularensis (Ft) is a category A biothreat agent for which there is no Food and Drug Administration-approved vaccine. Ft can survive in a variety of habitats with a remarkable ability to adapt to changing environmental conditions. Furthermore, Ft expresses distinct sets of antigens (Ags) when inside of macrophages (its in vivo host) as compared to those grown in vitro with Mueller Hinton Broth (MHB). However, in contrast to MHB-grown Ft, Ft grown in Brain-Heart Infusion (BHI) more closely mimics the antigenic profile of macrophage-grown Ft. Thus, we anticipated that when used as a vaccine, BHI-grown Ft would provide better protection compared to MHB-grown Ft, primarily due to its greater antigenic similarity to Ft circulating inside the host (macrophages) during natural infection. Our investigation, however, revealed that inactivated Ft (iFt) grown in MHB (iFt-MHB) exhibited superior protective activity when used as a vaccine, as compared to iFt grown in BHI (iFt-BHI). The superior protection afforded by iFt-MHB compared to that of iFt-BHI was associated with significantly lower bacterial burden and inflammation in the lungs and spleens of vaccinated mice. Moreover, iFt-MHB also induced increased levels of Ft-specific IgG. Further evaluation of early immunological cues also revealed that iFt-MHB exhibits increased engagement of Ag-presenting cells including increased iFt binding to dendritic cells, increased expression of costimulatory markers, and increased secretion of pro-inflammatory cytokines. Importantly, these studies directly demonstrate that Ft growth conditions strongly impact Ft vaccine efficacy and that the growth medium used to produce whole cell vaccines to Ft must be a key consideration in the development of a tularemia vaccine.

Vaccination evokes gender-dependent protection against tularemia infection in C57BL/6Tac mice

Francisella tularensis (Ft) is a Category A biothreat agent for which there currently is no FDA-approved vaccine. Thus, there is a substantial effort underway to develop an effective tularemia vaccine. While it is well established that gender can significantly impact susceptibility to primary infection, the impact of gender on vaccine efficacy is not well established. Thus, development of a successful vaccine against tularemia will require an understanding of the impact gender has on vaccine-induced protection against this organism. In this study, a role for gender in vaccine-induced protection following Ft challenge is identified for the first time. In the present study, mucosal vaccination with inactivated Ft (iFt) LVS elicited gender-based protection in C57BL/6Tac mice against respiratory challenge with Ft LVS. Specifically, vaccinated male mice were more susceptible to subsequent Ft LVS challenge. This increased susceptibility in male mice correlated with increased bacterial burden, increased tissue inflammation, and increased proinflammatory cytokine production late in post-challenge infection. In contrast, improved survival of iFt-vaccinated female mice correlated with reduced bacterial burden and enhanced levels of Ft-specific Abs in serum and broncho-alveolar lavage (BAL) fluid post-challenge. Furthermore, vaccination with a live attenuated vaccine consisting of an Ft LVS superoxide dismutase (SodB) mutant, which has proven efficacious against the highly virulent Ft SchuS4 strain, demonstrated similar gender bias in protection post-Ft SchuS4 challenge. Of particular significance is the fact that these are the first studies to demonstrate that gender differences impact disease outcome in the case of lethal respiratory tularemia following mucosal vaccination. In addition, these studies further emphasize the fact that gender differences must be a serious consideration in any future tularemia vaccine development studies.

Tularemia vaccine development: paralysis or progress?

Francisella tularensis (Ft) is a gram-negative intercellular pathogen and category A biothreat agent. However, despite 15 years of strong government investment and intense research focused on the development of a US Food and Drug Administration-approved vaccine against Ft, the primary goal remains elusive. This article reviews research efforts focused on developing an Ft vaccine, as well as a number of important factors, some only recently recognized as such, which can significantly impact the development and evaluation of Ft vaccine efficacy. Finally, an assessment is provided as to whether a US Food and Drug Administration-approved Ft vaccine is likely to be forthcoming and the potential means by which this might be achieved.

Modulation of Protective Efficacy of Fracisella tularensis Immunogens by Differential Cultivation in Mueler Hinton Broth Versus Brain Heart Infusion Medium

Francisella tularensis (Ft) can survive in a variety of habitats with a remarkable ability to adapt to changing environmental conditions. For example, Ft expresses a distinct set of antigens (Ags) in the macrophage, which are not expressed in Ft grown in vitro with Mueler Hinton Broth (MHB) medium. In contrast, Ft grown in Brain Heart Infusion (BHI) medium exhibits an antigenic profile more closely resembling that of in vivo growth conditions. In addition, studies also suggest an alteration in immunological properties of Ft when grown in BHI versus MHB medium. Thus, we investigated the protective efficacy of BHI and MHB-grown Ft, when inactivated and used as an immunogen to protect against Ft LVS challenge. Inactivated Ft (iFt) generated in MHB (iFt-MHB) was found to have superior protective efficacy as compared to that of the iFt generated in BHI (iFt-BHI). The enhanced protection generated by iFt- MHB-immunized mice was also associated with lower bacterial burden and sepsis-like conditions in the lungs and spleens of iFt-MHB versus iFt-BHI-immunized mice. Further evaluation of early immunological events revealed, in the case of iFt-MHB immunogen, superior Ag binding to Ag-presenting dendritic cells (DCs), increased MHC class II expression by DCs, and enhanced Ag presentation by DCs, as apposed to the use of iFt-BHI. Also, iFt-MHB induced increased levels of Ft-specific IgG as well as IFNg and IL17 production versus that of iFt-BHI. These studies thus demonstrate the critical importance of considering bacterial growth medium in Ft vaccine development.

Targeting of a Fixed Bacterial Immunogen to Fc Receptors Reverses the Anti-Inflammatory Properties of the Gram-Negative Bacterium, Francisella tularensis, during the Early Stages of Infection

Production of pro-inflammatory cytokines by innate immune cells at the early stages of bacterial infection is important for host protection against the pathogen. Many intracellular bacteria, including Francisella tularensis, the agent of tularemia, utilize the anti-inflammatory cytokine IL-10, to evade the host immune response. It is well established that IL-10 has the ability to inhibit robust antigen presentation by dendritic cells and macrophages, thus suppressing the generation of protective immunity. The pathogenesis of F. tularensis is not fully understood, and research has failed to develop an effective vaccine to this date. In the current study, we hypothesized that F. tularensis polarizes antigen presenting cells during the early stages of infection towards an anti-inflammatory status characterized by increased synthesis of IL-10 and decreased production of IL-12p70 and TNF-α in an IFN-ɣ-dependent fashion. In addition, F. tularensis drives an alternative activation of alveolar macrophages within the first 48 hours post-infection, thus allowing the bacterium to avoid protective immunity. Furthermore, we demonstrate that targeting inactivated F. tularensis (iFt) to Fcγ receptors (FcɣRs) via intranasal immunization with mAb-iFt complexes, a proven vaccine strategy in our laboratories, reverses the anti-inflammatory effects of the bacterium on macrophages by down-regulating production of IL-10. More specifically, we observed that targeting of iFt to FcγRs enhances the classical activation of macrophages not only within the respiratory mucosa, but also systemically, at the early stages of infection. These results provide important insight for further understanding the protective immune mechanisms generated when targeting immunogens to Fc receptors.

Preclinical testing of a vaccine candidate against tularemia

Tularemia is caused by a gram-negative, intracellular bacterial pathogen, Francisella tularensis (Ft). The history weaponization of Ft in the past has elevated concerns that it could be used as a bioweapon or an agent of bioterrorism. Since the discovery of Ft, three broad approaches adopted for tularemia vaccine development have included inactivated, live attenuated, or subunit vaccines. Shortcomings in each of these approaches have hampered the development of a suitable vaccine for prevention of tularemia. Recently, we reported an oxidant sensitive mutant of Ft LVS in putative EmrA1 (FTL_0687) secretion protein. The emrA1 mutant is highly sensitive to oxidants, attenuated for intramacrophage growth and virulence in mice. We reported that EmrA1 contributes to oxidant resistance by affecting the secretion of antioxidant enzymes SodB and KatG. This study investigated the vaccine potential of the emrA1 mutant in prevention of respiratory tularemia caused by Ft LVS and the virulent SchuS4 strain in C57BL/6 mice. We report that emrA1 mutant is safe and can be used at an intranasal (i. n.) immunization dose as high as 1x106 CFU without causing any adverse effects in immunized mice. The emrA1 mutant is cleared by vaccinated mice by day 14-21 post-immunization, induces minimal histopathological lesions in lungs, liver and spleen and a strong humoral immune response. The emrA1 mutant vaccinated mice are protected against 1000-10,000LD100 doses of i.n. Ft LVS challenge. Such a high degree of protection has not been reported earlier against respiratory challenge with Ft LVS using a single immunization dose with an attenuated mutant generated on Ft LVS background. The emrA1 mutant also provides partial protection against i.n. challenge with virulent Ft SchuS4 strain in vaccinated C57BL/6 mice. Collectively, our results further support the notion that antioxidants of Ft may serve as potential targets for development of effective vaccines for prevention of tularemia.

Fc receptor-targeting of immunogen as a strategy for enhanced antigen loading, vaccination, and protection using intranasally administered antigen-pulsed dendritic cells

Dendritic cells (DCs) play a critical role in the generation of adaptive immunity via the efficient capture, processing, and presentation of antigen (Ag) to naïve T cells. Administration of Ag-pulsed DCs is also an effective strategy for enhancing immunity to tumors and infectious disease organisms. Studies have also demonstrated that targeting Ags to Fcγ receptors (FcγR) on Ag presenting cells can enhance humoral and cellular immunity in vitro and in vivo. Specifically, our studies using a Francisella tularensis (Ft) infectious disease vaccine model have demonstrated that targeting immunogens to FcγR via intranasal (i.n.) administration of monoclonal antibody (mAb)-inactivated Ft (iFt) immune complexes (ICs) enhances protection against Ft challenge. Ft is the causative agent of tularemia, a debilitating disease of humans and other mammals and a category A biothreat agent for which there is no approved vaccine. Therefore, using iFt Ag as a model immunogen, we sought to determine if ex vivo targeting of iFt to FcγR on DCs would enhance the potency of i.n. administered iFt-pulsed DCs. In this study, bone marrow-derived DCs (BMDCs) were pulsed ex vivo with iFt or mAb-iFt ICs. Intranasal administration of mAb-iFt-pulsed BMDCs enhanced humoral and cellular immune responses, as well as protection against Ft live vaccine strain (LVS) challenge. Increased protection correlated with increased iFt loading on the BMDC surface as a consequence of FcγR-targeting. However, the inhibitory FcγRIIB had no impact on this enhancement. In conclusion, targeting Ag ex vivo to FcγR on DCs provides a method for enhanced Ag loading of DCs ex vivo, thereby reducing the amount of Ag required, while also avoiding the inhibitory impact of FcγRIIB. Thus, this represents a simple and less invasive strategy for increasing the potency of ex vivo-pulsed DC vaccines against chronic infectious diseases and cancer.

Multiple mechanisms mediate enhanced immunity generated by mAb-inactivated F. tularensis immunogen

We have previously demonstrated that immunization with inactivated Francisella tularensis, a Category A intracellular mucosal pathogen, combined with IgG2a anti-F. tularensis monoclonal antibody, enhances protection against subsequent F. tularensis challenge. To understand the mechanism(s) involved, we examined the binding, internalization, presentation, and in vivo trafficking of inactivated F. tularensis in the presence and absence of opsonizing monoclonal antibody. We found that when inactivated F. tularensis is combined with anti-F. tularensis monoclonal antibody, presentation to F. tularensis-specific T cells is enhanced, this enhancement is Fc receptor-dependent, and requires a physical linkage between the monoclonal antibody and the inactivated F. tularensis immunogen. This enhanced presentation is due, in part, to enhanced binding and internalization of inactivated F. tularensis by antigen presenting cells, and involves interactions with multiple Fc receptor types. Furthermore, targeting inactivated F. tularensis to Fc receptors enhances dendritic cell maturation and extends the time period over which antigen presenting cells stimulate T cells. In vivo trafficking studies reveal enhanced transport of inactivated F. tularensis immunogen to the Nasal Associated Lymphoid Tissue in the presence of monoclonal antibody, which is FcRn-dependent. In summary, these are the first comprehensive studies using a single vaccine protection model/immunogen to establish the array of mechanisms involved in enhanced immunity/protection mediated by an Fc receptor-targeted mucosal immunogen. These results demonstrate that multiple cellular/immune mechanisms contribute to Fc receptor-enhanced immunity.

Host-adaptation of Francisella tularensis alters the bacterium's surface-carbohydrates to hinder effectors of innate and adaptive immunity

BACKGROUND

The gram-negative bacterium Francisella tularensis survives in arthropods, fresh water amoeba, and mammals with both intracellular and extracellular phases and could reasonably be expected to express distinct phenotypes in these environments. The presence of a capsule on this bacterium has been controversial with some groups finding such a structure while other groups report that no capsule could be identified. Previously we reported in vitro culture conditions for this bacterium which, in contrast to typical methods, yielded a bacterial phenotype that mimics that of the bacterium's mammalian, extracellular phase.

METHODS/FINDINGS

SDS-PAGE and carbohydrate analysis of differentially-cultivated F. tularensis LVS revealed that bacteria displaying the host-adapted phenotype produce both longer polymers of LPS O-antigen (OAg) and additional HMW carbohydrates/glycoproteins that are reduced/absent in non-host-adapted bacteria. Analysis of wildtype and OAg-mutant bacteria indicated that the induced changes in surface carbohydrates involved both OAg and non-OAg species. To assess the impact of these HMW carbohydrates on the access of outer membrane constituents to antibody we used differentially-cultivated bacteria in vitro to immunoprecipitate antibodies directed against outer membrane moieties. We observed that the surface-carbohydrates induced during host-adaptation shield many outer membrane antigens from binding by antibody. Similar assays with normal mouse serum indicate that the induced HMW carbohydrates also impede complement deposition. Using an in vitro macrophage infection assay, we find that the bacterial HMW carbohydrate impedes TLR2-dependent, pro-inflammatory cytokine production by macrophages. Lastly we show that upon host-adaptation, the human-virulent strain, F. tularensis SchuS4 also induces capsule production with the effect of reducing macrophage-activation and accelerating tularemia pathogenesis in mice.

CONCLUSION

F. tularensis undergoes host-adaptation which includes production of multiple capsular materials. These capsules impede recognition of bacterial outer membrane constituents by antibody, complement, and Toll-Like Receptor 2. These changes in the host-pathogen interface have profound implications for pathogenesis and vaccine development.

Development of tolerogenic dendritic cells and regulatory T cells favors exponential bacterial growth and survival during early respiratory tularemia

Tularemia is a vector-borne zoonosis caused by Ft, a Gram-negative, facultative intracellular bacterium. Ft exists in two clinically relevant forms, the European biovar B (holarctica), which produces acute, although mild, self-limiting infections, and the more virulent United States biovar A (tularensis), which is often associated with pneumonic tularemia and more severe disease. In a mouse model of tularemia, respiratory infection with the virulence-attenuated Type B (LVS) or highly virulent Type A (SchuS4) strain engenders peribronchiolar and perivascular inflammation. Paradoxically, despite an intense neutrophilic infiltrate and high bacterial burden, T(h)1-type proinflammatory cytokines (e.g., TNF, IL-1β, IL-6, and IL-12) are absent within the first ∼72 h of pulmonary infection. It has been suggested that the bacterium has the capacity to actively suppress or block NF-κB signaling, thus causing an initial delay in up-regulation of inflammatory mediators. However, our previously published findings and those presented herein contradict this paradigm and instead, strongly support an alternative hypothesis. Rather than blocking NF-κB, Ft actually triggers TLR2-dependent NF-κB signaling, resulting in the development and activation of tDCs and the release of anti-inflammatory cytokines (e.g., IL-10 and TGF-β). In turn, these cytokines stimulate development and proliferation of T(regs) that may restrain T(h)1-type proinflammatory cytokine release early during tularemic infection. The highly regulated and overall anti-inflammatory milieu established in the lung is permissive for unfettered growth and survival of Ft. The capacity of Ft to evoke such a response represents an important immune-evasive strategy.

Enhanced Antigen-Specific Antibody and Cytokine Responses When Targeting Antigen to Human FcGAMMA Receptor Type I Using an Anti-Human FcGAMMA Receptor Type I-Streptavidin Fusion Protein in an Adjuvant-Free System

There is a continuing need for alternatives to current human adjuvants. Recombinant protein vaccines, which target antigen to human Fc gamma receptor type I (hFcgammaRI) on hFcgammaRI-expressing antigen presenting cells, provide one potential alternative. Using a recombinant anti-hFcgammaRI-antigen fusion protein and adjuvant independent mouse model, we demonstrate enhanced antigen-specific antibody responses to low doses of antigen, when targeting antigen to hFcgammaRI in vivo. Enhanced antibody production to hFcyRI-targeted antigen is evident in both primary and secondary immune responses, as compared to that of non-targeted antigen. Furthermore, antibody isotype and cytokine responses following immunization with hFcgammaRI-targeted antigen, suggest enhancement of both Th1 and Th2 responses.

Differential requirements for protection against mucosal challenge with Francisella tularensis in the presence versus absence of cholera toxin B and inactivated F. tularensis

Francisella tularensis is a category A biothreat agent for which there is no approved vaccine and the correlates of protection are not well understood. In particular, the relationship between the humoral and cellular immune response to F. tularensis and the relative importance of each in protection is controversial. Yet, understanding this relationship will be crucial to the development of an effective vaccine against this organism. We demonstrate, for the first time, a differential requirement for humoral vs cellular immunity in vaccine-induced protection against F. tularensis infection, and that the requirement for Ab observed in some protection studies, may be overcome through the induction of enhanced cellular immunity. Specifically, following intranasal/mucosal immunization of mice with inactivated F. tularensis organisms plus the cholera toxin B subunit, we observe increased production of IgG2a/2c vs IgG1 Ab, as well as IFN-gamma, indicating induction of a Th1 response. In addition, the requirement for F. tularensis-specific IgA Ab production, observed in studies following immunization with inactivated F. tularensis alone, is eliminated. Thus, these data indicate that enhanced Th1 responses can supersede the requirement for anti-F. tularensis-specific IgA. This observation also has important ramifications for vaccine development against this organism.

Utilization of Fc receptors as a mucosal vaccine strategy against an intracellular bacterium, Francisella tularensis

Numerous studies have demonstrated that targeting Ag to Fc receptors (FcR) on APCs can enhance humoral and cellular immunity. However, studies are lacking that examine both the use of FcR-targeting in generating immune protection against infectious agents and the use of FcRs in the induction of mucosal immunity. Francisella tularensis is a category A intracellular mucosal pathogen. Thus, intense efforts are underway to develop a vaccine against this organism. We hypothesized that protection against mucosal infection with F. tularensis would be significantly enhanced by targeting inactivated F. tularensis live vaccine strain (iFt) to FcRs at mucosal sites, via intranasal immunization with mAb-iFt complexes. These studies demonstrate for the first time that: 1) FcR-targeted immunogen enhances immunogen-specific IgA production and protection against subsequent infection in an IgA-dependent manner, 2) FcgammaR and neonatal FcR are crucial to this protection, and 3) inactivated F. tularensis, when targeted to FcRs, enhances protection against the highly virulent SchuS4 strain of F. tularensis, a category A biothreat agent. In summary, these studies show for the first time the use of FcRs as a highly effective vaccination strategy against a highly virulent mucosal intracellular pathogen.

Natural Killer and CD8 T Cells Dominate the Response by Human Peripheral Blood Mononuclear Cells to Inactivated Francisella tularensis Live Vaccine Strain

Francisella tularensis is a category A biothreat agent, and as a result, it has recently generated much research interest. F. tularensis live vaccine strain (LVS) is an attenuated form of the virulent F. tularensis organism and has previously been used as a vaccine. However, because of safety concerns, it is no longer approved for this purpose. Thus, the use of inactivated organisms is preferable for vaccine purposes. Although many studies have been performed that examine human peripheral blood mononuclear cells (PBMC), and in particular CD4 T cells, responses to inactivated F. tularensis, there has been no study identifying the individual human cell populations within a mixed PBMC population that respond to this organism. We sought to address this deficit. Our results indicate that natural killer and CD8 T cells comprise the majority of cells responding to F. tularensis LVS. In addition, data suggest CD8 T cell responses are maximal when antibiotic-treated organisms are used and are minimal when formaldehyde-fixed organisms are used. Given the belief that CD8 T cells can play an important role in protection against F. tularensis infection, these studies have direct relevance to the development of F. tularensis vaccines that use inactivated organisms. In addition, important new knowledge is added to our understanding of the human immune response to F. tularensis LVS.

Low-level signaling generated by FcgammaRIIB-B cell receptor co-ligation establishes a state of global B cell receptor nonresponsiveness

In addition to the stimulatory, antigen-specific B cell receptor (BCR), B lymphocytes also express multiple inhibitory receptors, including Fc gamma receptor type IIB (FcgammaRIIB). Moreover, many laboratories have demonstrated that co-ligation of BCR molecules to inhibitory FcgammaRIIB molecules with high concentrations (10-15 microg/ml) of ligand results in altered BCR signaling. However, there are no reports on the effect of low concentrations of ligand on BCR-FcgammaRIIB co-ligation and subsequent signaling. This knowledge will be critical for optimizing the in vivo use of such reagents. Accordingly, the effect of low ligand concentration on the level of BCR-FcgammaRIIB co-ligation and subsequent BCR signaling was analyzed. The results demonstrate that co-ligation of BCR and FcgammaRIIB molecules at low concentrations (0.5-1.5 microg/ml) of cross-linking reagent, establishes a condition that prevents the B cell from responding to subsequent stimulation, even when the initial exposure to cross-linking reagent fails to generate a calcium flux. Moreover, analysis of the effect of BCR-FcgammaRIIB co-ligation in cells expressing a nonsignaling competent BCR suggest that FcgammaRIIB-mediated inhibition of BCR signaling requires co-ligation of FcgammaRIIB with signaling competent BCR molecules. These results suggest that in vivo treatments with low levels of BCR-FcgammaRIIB cross-linking reagent can induce BCR-FcgammaRIIB co-ligation and establish a condition of B cell nonresponsiveness.

Production of genetically engineered biotinylated interleukin-2 and its application in a rapid nonradioactive assay for T-cell activation

The development of reliable assay systems that can measure lymphocyte activation in vitro has been a major goal of immunodiagnostics. Traditionally, tritiated thymidine incorporation has been used to monitor T-cell activation. Other methods include enzyme-linked immunosorbent assay (ELISA), enzyme-linked immunospot assay, and colorimetric assays. We have established a lymphocyte activation assay that utilizes fluorescein isothiocyanate (FITC)-streptavidin bound to recombinant biotinylated human interleukin-2 (IL-2). Utilizing recombinant DNA technology, a unique monobiotinylated human IL-2 has been created and isolated using the Promega PinPoint vector system. ELISA has been used to demonstrate streptavidin binding and recognition by a human IL-2-specific antibody. IL-2 function has been demonstrated using a murine IL-2-dependent T-cell line, CTLL-2, responsive to human IL-2. Recombinant biotinylated human IL-2 conjugated to streptavidin-FITC or streptavidin-horseradish peroxidase has been used to monitor T-cell activation in the presence of antigen as well as mitogen. The sensitivity and convenience of this method make this lymphocyte activation assay an attractive alternative to tritiated thymidine incorporation as a method for monitoring T-cell activation. In addition, the availability of a recombinant biotinylated human IL-2 will permit the production of a uniform product suitable for diagnostic and clinical application.

A two-component modular approach for enhancing T-cell activation utilizing a unique anti-FcgammaRI-streptavidin construct and microspheres coated with biotinylated-antigen

The professional antigen presenting cell (APC) plays an essential role in the initiation and propagation of the acquired immune response. Thus, much work has been done in designing strategies that target vaccine antigen (Ag) to APC. Utilizing recombinant DNA technology, we have created a unique two-component system that delivers biotinylated Ag to the Fc gamma receptor type I (FcgammaRI) on APC. Our studies demonstrate that we can successfully engineer FcgammaRI-specific targeting element proteins that simultaneously bind both biotin and recognize FcgammaRI. Additionally, we are able to engineer biotinylated Ag, which form functional elements when adsorbed onto latex microspheres. Furthermore, the targeting and functional element components bind to each other and successfully form two-component immunogens. T-cell activation in response to targeted Ag-laden microspheres is 10- to 100-fold greater than the response to the non-targeted Ag-laden microspheres. This enhancement is 100- to 1000-fold greater than the responses generated to soluble Ag. Thus, our results suggest that specific targeting of Ag-laden microspheres to FcgammaRI may significantly enhance the adjuvant properties of microparticulate delivery systems. Further development of this system may help to elucidate the mechanisms involved in generating enhanced responses to APC-targeted vaccines and significantly advance vaccine technology.

Generation of a human IgG3-streptavidin fusion protein. Implications for the inhibition and elimination of auto-reactive B cells

Antibodies against self-molecules play a significant role in the development and progression of Systemic Lupus Erythematosus, as well as a number of other autoimmune disorders. Immunosuppressive drugs have been used to control this process. However, they are normally not specific to the offending cell, and can actually suppress beneficial immune responses to pathogens. In this paper a genetically engineered targeting molecule is described, which has the capacity to target antigen-specific B cells for inhibition or elimination. The targeting molecule is a fusion of streptavidin subunit to the constant region of human IgG3 (IgG3-Av). It is demonstrated by ELISA and flow cytometry that IgG3-Av binds biotinylated antigen as well as human Fc gamma receptors present on myeloid cells. It is also shown by confocal microscopy and flow cytometry, that IgG3-Av can mediate Fc receptor-dependent phagocytosis of latex microspheres adsorbed with biotinylated antigen. Furthermore, the IgG3-Av construct can modulate Ca++ flux, characteristic of B cell inhibition as well as ADCC of B cells in an antigen-specific manner. In summary, these studies describe an approach, which has the potential to be used as a treatment to inhibit or remove antigen-specific (auto-reactive) B cells.

Regulation of CD23 isoforms on B-chronic lymphocytic leukemia

CD23 is constitutively and atypically expressed on malignant B-cells in patients with chronic lymphocytic leukemia. It exists in two isoforms that differ only in a short amino acid sequence at the N-terminus. The CD23a isoform exhibits an endocytosis signal, that renders it more efficient in antigen uptake than CD23b. Therefore, we analyzed the regulation of CD23 isoforms and tested the ability to stimulate T-cell clones by targeting antigen to CD23 on CLL B-cells. Investigation of several stimulators to promote CD23a expression on CLL versus normal B-cells confirmed a different CD23 regulation in B-CLL. We did not find any evidence for a differential regulation of the two CD23 isoforms in B-CLL. However, CD23a is always predominantly expressed with a constant ratio of CD23a:CD23b. We show that antigen targeted to CD23 on CLL B-cells is very efficiently presented. Therefore, CD23 is likely to provide a suitable target for receptor-mediated antigen presentation in B-CLL which can be used to activate a T-cell response.

Lipoteichoic acid inhibits interleukin-2 (IL-2) function by direct binding to IL-2

Lipoteichoic acid (LTA) is associated with the cell envelope of most gram-positive bacteria. Although previously thought to act mainly as a virulence factor by virtue of its adhesive nature, evidence is now provided that LTA can also suppress the function of interleukin-2 (IL-2), an autocrine growth factor for T cells. LTA from four separate bacterial strains lowered the levels of detectable IL-2 during a peripheral blood mononuclear cell response to the antigen tetanus toxoid (TT). T-cell proliferation in response to TT was similarly inhibited by LTA. In contrast, levels of detectable gamma interferon increased. In addition, LTA inhibited IL-2 detection by enzyme-linked immunosorbent assay (ELISA) and blocked the proliferative response of an IL-2-dependent T-cell line to soluble IL-2. Further studies using ELISA demonstrated that LTA blocks IL-2 detection and function by binding directly to IL-2. Flow cytometric analysis revealed that IL-2 binding to T cells is inhibited in the presence of purified LTA but not LTA plus anti-LTA monoclonal antibody. In summary, these studies demonstrate a novel effect of LTA on the immune response through direct binding to IL-2 and inhibition of IL-2 function. Importantly, gram-positive organisms from which LTA is obtained not only play an important role in the pathology of diseases such as bacterial endocarditis, septic shock, acute respiratory distress syndrome, and multiple organ failure but also comprise a significant portion of commensal populations within the human host. Inhibition of IL-2 function by LTA may represent yet another mechanism by which gram-positive bacteria dampen the host immune response and facilitate survival. Thus, LTA provides a potential target for therapeutic intervention when gram-positive organisms are involved.

Stealth cells: prevention of major histocompatibility complex class II-mediated T-cell activation by cell surface modification

Transfusion or transplantation of T lymphocytes into an allogeneic recipient can evoke potent immune responses including, in immunocompromised patients, graft-versus-host disease (GVHD). As our previous studies demonstrated attenuated immunorecognition of red blood cells covalently modified with methoxy(polyethylene glycol) (mPEG), we hypothesized that T-cell activation by foreign antigens might similarly be prevented by mPEG modification. Mixed lymphocyte reactions (MLR) using peripheral blood mononuclear cells (PBMC) from HLA class II disparate donors demonstrate that mPEG modification of PBMC effectively inhibits T-cell proliferation (measured by (3)H-thymidine incorporation) in a dose-dependent manner. Even slight derivatization (0.4 mmol/L mPEG per 4 x 10(6) cells) resulted in a >/=75% decrease, while higher concentrations caused >/=96% decrease in proliferation. Loss of PBMC proliferation was not due to either mPEG-induced cytotoxicity, as viability was normal, or cellular anergy, as phytohemagglutinin (PHA)-stimulated mPEG-PBMC demonstrated normal proliferative responses. Addition of exogenous interleukin (IL)-2 also had no proliferative effect, suggesting that the mPEG-modified T cells were not antigen primed. Flow cytometric analysis demonstrates that mPEG-modification dramatically decreases antibody recognition of multiple molecules involved in essential cell:cell interactions, including both T-cell molecules (CD2, CD3, CD4, CD8, CD28, CD11a, CD62L) and antigen-presenting cell (APC) molecules (CD80, CD58, CD62L) likely preventing the initial adhesion and costimulatory events necessary for immune recognition and response.

Differences in IgG subclass do not effect immune complex-enhanced T cell activation despite differential binding to antigen presenting cells

Ag presentation to CD4 T cells is a critical event in the generation of protective immunity. IgG, in the form of IgG-pathogen (Ag) complexes, is capable of mediating FcgammaR-dependent Ag presentation, and thereby enhanced T cell activation. Therefore, it is important to understand the ability of the individual human IgG subclasses to function in enhanced T cell activation. We hypothesized that increased delivery of Ag to monocyte FcgammaR by high affinity human IgG subclasses, IgG1 and IgG3, would lead to increased Ag presentation, as compared to low affinity IgG subclasses, IgG2 and IgG4. To create immune complexes, we linked biotinylated IgG subclasses to biotinylated Ag via an avidin bridge, and examined T cell responses to them. Although IgG2- and IgG4-Ag complexes bound to monocytes at significantly lower levels than those made with IgG1 and IgG3, we observed no significant difference in the ability of the four human IgG subclasses to mediate enhanced T cell activation. Studies suggest the explanation for this dichotomy lies within the first 24 h of Ag processing, and that processing efficiency may vary with IgG subclass. They also suggest the existence of a highly efficient, and selective processing pathway, which is dependent on IgG subclass, and can compensate for low level production and FcgammaR binding of IgG2- and IgG4-Ag complexes.

Inhibition of interleukin-2 by a Gram-positive bacterium, Streptococcus mutans

Generation of an effective cellular immune response is key to the successful development of both humoral and cellular immune defences against most pathogens. However, while the type of cellular immune response elicited by any given pathogen is dictated by the entire array of antigens and molecules which comprise that pathogen, most studies of human immune responses to bacterial pathogens tend to focus on selected antigens. This is a result, in part, of a desire to find those antigens that will generate a desired immune response, as well as limited technology for monitoring the complex array of responses generated by an intact organism. Utilizing Streptococcus mutans as a model Gram-positive organism, a novel flow cytometric assay that permits the identification of individual cells within a responding population, and highly sensitive cytokine assays, we show for the first time that CD8 T cells and natural killer (NK) cells comprise a significant component of the response to this organism in humans. This is despite the fact that CD8 T cells are traditionally thought to respond to endogenously derived antigens only. In addition, we provide the first evidence that a Gram-positive organism can actively inhibit interleukin-2 (IL-2), an important autocrine growth factor for T cells. The latter observation could represent an additional mechanism by which Gram-positive organisms evade host defences.

Flow cytometric analysis of leukocytes in the human female reproductive tract: comparison of fallopian tube, uterus, cervix, and vagina

PROBLEM

The tissues of the human female reproductive tract (Fallopian tube, uterus, cervix, and vagina) may play different roles in the provision of mucosal immunity. The purpose of this study was to develop a uniform method suitable for quantitative comparison of the leukocytes from all these tissues.

METHOD OF STUDY

Tissues, typically 0.5-1.0 g, were dispersed by enzyme treatment. A flow cytometric gating procedure based on CD45-positivity and low far-red autofluorescence permitted unfractionated, freshly dispersed cells to be phenotyped with respect to T lymphocytes, B lymphocytes, macrophages, and granulocytes.

RESULTS

Reproductive tract tissues contain leukocytes that represent approximately 6-20% of the total number of cells, with the Fallopian tubes and uterus containing a higher proportion of leukocytes than the cervix and vagina. The uterine endometrium from post-menopausal women has fewer leukocytes than does uterine endometrium from pre-menopausal women. T lymphocytes are a major constituent (30-60%) of leukocytes from all tissues. The Fallopian tube contains granulocytes as another major constituent; granulocytes are significantly less numerous in the other tissues. All tissues contain B lymphocytes and macrophages as clearly detectable but minor components.

CONCLUSIONS

Three-color flow cytometry is an appropriate method for quantitative comparison of leukocytes from the different tissues of the female reproductive tract, during all phases of the menstrual cycle and within post-menopausal samples. Results indicate that the tissues differ from each other, particularly with respect to the large number of granulocytes in the Fallopian tubes.

Activation of human T cells by major histocompatability complex class II expressing neutrophils: proliferation in the presence of superantigen, but not tetanus toxoid

The primary function of polymorphonuclear neutrophils (PMN) in the immune response appears to be acute phagocytic clearance of foreign pathogens and release of inflammatory mediators. Consistent with their assumed lack of major histocompatibility complex (MHC) class II expression, PMN have not been considered to play a role in antigen presentation and T-cell activation. However, recent reports have shown that human PMN can express MHC class II molecules both in vitro and in vivo after stimulation with either granulocyte-macrophage colony-stimulating factor (GM-CSF) or interferon-gamma (IFN-gamma). Thus, under appropriate conditions, PMN could play a significant role in immune regulation, including T-cell activation. In this report, we demonstrate that human class II-expressing PMN can serve as accessory cells in superantigen (SAg)-mediated T-cell activation. This accessory activity for SAg presentation was present only after induction of MHC class II expression, and was especially pronounced following culture of PMN with GM-CSF plus IFN-gamma, which acted synergistically to induce MHC class II molecules on PMN. Moreover, the level of MHC class II expression and the magnitude of SAg-induced T-cell responses were found to be highly correlated and distinctly donor dependent, with PMN from some donors repeatedly showing fivefold higher responses than PMN from other donors. On the other hand, culture of PMN with GM-CSF plus IFN-gamma under conditions that resulted in optimal MHC class II expression did not enable them to function as antigen-presenting cells for either intact tetanus toxoid (TT) or for a TT peptide. These results delineate a new pathway for T-cell activation by SAg that may play an important role in the severity of SAg-induced inflammatory responses. They also identify a donor-specific polymorphism for induction of PMN MHC class II expression which may be of significance for therapies involving GM-CSF and IFN-gamma.

Fc gamma RII on human B cells can mediate enhanced antigen presentation

The ability of Fc gamma R on monocytes and macrophages to enhance presentation of Ab-bound Ag has been well established. In contrast, studies suggest that Fc gamma RII on B cells functions primarily to suppress B cell responses. We found that presentation of tetanus toxoid (TT) by human EBV-transformed B cells was enhanced by 100- to 1000-fold, when TT was targeted to Fc gamma RII on B cells by using a conjugate consisting of TT covalently linked to anti-human Fc gamma RII mAb 41H16. This enhanced presentation could be blocked by mAb 41H16, heat-aggregated human IgG, or anti-MHC Class II mAb. Similarly, multimeric immune complexes composed to TT and anti-TT mAb, SA13, and 9F12 also enhanced presentation of TT. Furthermore, Fc gamma RII on purified human peripheral blood B cells could also enhance Ag presentation. These studies provide the first clear evidence that Fc gamma RII can participate in enhanced Ag presentation by human B cells and suggest that Fc gamma RII has the potential to play a stimulatory role in human B cell responses to Ag-Ab complexes.

Induction of MHC class II on human polymorphonuclear neutrophils by granulocyte/macrophage colony-stimulating factor, IFN-gamma, and IL-3

Polymorphonuclear neutrophils (PMN) have long been thought to be short-lived, terminally differentiated cells incapable of synthesizing significant levels of protein, with their primary function being phagocytosis and the release of cytotoxic compounds. More recently, it has been demonstrated that PMN can produce a number of functionally diverse substances, including IL-1, IL-6, and IL-8. Although PMN express class I MHC Ag, it has not been definitely demonstrated that they can synthesize and express class II Ag. This would suggest that, although PMN can indirectly assist in the induction of an immune response through production of cytokines, they are incapable of acting as APC for CD4+ Th cells. We show that, in the presence of a defined medium (AIM V), human serum, and granulocyte-CSF, nearly 100% of isolated PMN can survive for up to 2 days in vitro. We also show that PMN express MHC class II when present as bystander cells in a monocyte/T cell Ag presentation assay for 44 h. In addition, granulocyte/macrophage CSF (GM-CSF), IFN-gamma, and IL-3 can induce class II on pure cultures of PMN, with GM-CSF appearing to be the most potent of the three cytokines. Furthermore, induction of class II on PMN is distinctly donor dependent, with PMN from some donors repeatedly showing very high, and others very low, induction of class II when treated with GM-CSF. Their potential to express class II suggests that PMN could play a significant role in immunoregulation and disease pathogenesis. The variation in class II induction on PMN from individual donors might explain previous failures to detect class II induction on PMN and could be a factor in the varied susceptibility of different individuals to autoimmune and inflammatory disorders such as the production of antibodies to PMN cytoplasmic components.

Induction of MHC class II on human polymorphonuclear neutrophils by granulocyte/macrophage colony-stimulating factor, IFN-gamma, and IL-3

Polymorphonuclear neutrophils (PMN) have long been thought to be short-lived, terminally differentiated cells incapable of synthesizing significant levels of protein, with their primary function being phagocytosis and the release of cytotoxic compounds. More recently, it has been demonstrated that PMN can produce a number of functionally diverse substances, including IL-1, IL-6, and IL-8. Although PMN express class I MHC Ag, it has not been definitely demonstrated that they can synthesize and express class II Ag. This would suggest that, although PMN can indirectly assist in the induction of an immune response through production of cytokines, they are incapable of acting as APC for CD4+ Th cells. We show that, in the presence of a defined medium (AIM V), human serum, and granulocyte-CSF, nearly 100% of isolated PMN can survive for up to 2 days in vitro. We also show that PMN express MHC class II when present as bystander cells in a monocyte/T cell Ag presentation assay for 44 h. In addition, granulocyte/macrophage CSF (GM-CSF), IFN-gamma, and IL-3 can induce class II on pure cultures of PMN, with GM-CSF appearing to be the most potent of the three cytokines. Furthermore, induction of class II on PMN is distinctly donor dependent, with PMN from some donors repeatedly showing very high, and others very low, induction of class II when treated with GM-CSF. Their potential to express class II suggests that PMN could play a significant role in immunoregulation and disease pathogenesis. The variation in class II induction on PMN from individual donors might explain previous failures to detect class II induction on PMN and could be a factor in the varied susceptibility of different individuals to autoimmune and inflammatory disorders such as the production of antibodies to PMN cytoplasmic components.

Enhanced antigen presentation using human Fc gamma receptor (monocyte/macrophage)-specific immunogens

A major new challenge for vaccine development is to target APC such as monocytes and macrophages for efficient Ag processing and presentation. It has been shown that Fc gamma R-mediated uptake of Ag-antibody complexes can enhance Ag presentation by myeloid cells at least 100-fold, and directing Ag to Fc gamma R in mice brings about a substantial increase in the effectiveness of immunization while eliminating the requirement for adjuvant. It has not been determined which of the three subclasses of human Fc gamma R on myeloid cells (Fc gamma RI, Fc gamma RII, or Fc gamma RIII) function to enhance Ag presentation. We have targeted our Ag (TT) to each of the three subclasses of human Fc gamma R on monocytes using Fc gamma R subclass-specific mAb-TT conjugates, and have measured TT presentation by monitoring T cell proliferation in response to TT. In addition, we have examined enhanced Ag presentation mediated by a human IgG1 (HIgG1) anti-TT mAb. All anti-Fc gamma R-TT conjugates enhanced Ag presentation. HIgG1 anti-TT, in monomeric form, enhanced Ag presentation through Fc gamma RI only. Anti-Fc gamma RI-Ag conjugates appear to be optimal for application as vaccines. They are monocyte/macrophage-specific, are very efficiently processed and presented, and enhance Ag presentation despite occupation of Fc gamma RI with HIgG.

Enhanced antigen presentation using human Fc gamma receptor (monocyte/macrophage)-specific immunogens

A major new challenge for vaccine development is to target APC such as monocytes and macrophages for efficient Ag processing and presentation. It has been shown that Fc gamma R-mediated uptake of Ag-antibody complexes can enhance Ag presentation by myeloid cells at least 100-fold, and directing Ag to Fc gamma R in mice brings about a substantial increase in the effectiveness of immunization while eliminating the requirement for adjuvant. It has not been determined which of the three subclasses of human Fc gamma R on myeloid cells (Fc gamma RI, Fc gamma RII, or Fc gamma RIII) function to enhance Ag presentation. We have targeted our Ag (TT) to each of the three subclasses of human Fc gamma R on monocytes using Fc gamma R subclass-specific mAb-TT conjugates, and have measured TT presentation by monitoring T cell proliferation in response to TT. In addition, we have examined enhanced Ag presentation mediated by a human IgG1 (HIgG1) anti-TT mAb. All anti-Fc gamma R-TT conjugates enhanced Ag presentation. HIgG1 anti-TT, in monomeric form, enhanced Ag presentation through Fc gamma RI only. Anti-Fc gamma RI-Ag conjugates appear to be optimal for application as vaccines. They are monocyte/macrophage-specific, are very efficiently processed and presented, and enhance Ag presentation despite occupation of Fc gamma RI with HIgG.

Class II MHC molecules and antigen enter the same vesicles during internalization by resting B lymphocytes

Efficient presentation of Ag by a B cell to a T cell requires that Ag bind to the Ag receptor (Ig) on the B cell, after which it is internalized into an acid compartment where it is modified and returned to the cell surface in the context of class II MHC molecules. It remains uncertain whether processed Ag binds to class II which has been internalized and recycled with Ag, or to nascent class II inside the cell. To determine if cell surface class II enters the same vesicles as Ag, or is excluded during internalization of Ag which is bound to the B cell receptor, 5- and 16-nm gold particles were labeled with anti-class II and anti-Ig, respectively. Cells were incubated at 37 degrees C and internalization of these particles was observed using electron microscopy. By 10 min, 60-75% of the B cell sections contained vesicles with gold particles inside them. Between 40 and 64% of these vesicles had both 5- and 16-nm particles. Maximum internalization occurred by 30-60 min, and by 2 hr the number of small and large particles on the B cell surface became constant or increased, respectively. Both kinds of particles moved from electron-lucent to electron-dense vesicles as the incubation time increased, although a portion of the anti-class II particles remained in electron-lucent vesicles. These data clearly show that labeled, cell surface class II is not selectively excluded from Ag-containing vesicles during Ag internalization. Thus, cointernalization of Ag and class II may represent a mechanism by which processed Ag meets class II.

Molecular basis for a polymorphism of human Fc gamma receptor II (CD32)

The IgG Fc receptor II on human monocytes is polymorphic in its ability to bind mIgG1, and its isoelectric focusing pattern. To study the molecular basis of this polymorphism, a cDNA library from cell line K562, expressing two different allelic forms (high responder [HR] and low responder [LR]) of Fc gamma RII, was used for cDNA cloning. We report the isolation and identification of different Fc gamma RII cDNA clones, comprising the LR form of Fc gamma RII, as was evident from studies using a new HR-specific anti-Fc gamma RII mAb 41H16, and from rosetting experiments. Sequence analysis revealed that HR and LR forms differ by two amino acids, both located in the external domain. In the cloned LR form, a glutamine is substituted by a tryptophan residue at aa position 27, located in the first Ig-like domain, and an arginine residue by a histidine residue at aa position 131 in the second Ig-like domain. Furthermore, an Fc gamma RII cDNA clone was isolated with a deletion of 123 bp, overlapping the predicted transmembrane segment. Data showing the presence of an alternatively spliced mRNA detected by using polymerase chain reaction (PCR) might suggest the existence of a soluble form of the human Fc gamma RII, in addition to the membrane-bound forms.

The monoclonal antibody 41H16 detects the Leu 4 responder form of human Fc gamma RII

Human FcR for IgG can be divided into three classes (Fc gamma RI, II, and III) based on their structure and reactivity with mAb. Fc gamma RII can be further subdivided into two categories based on functional and biochemical assays. These two Fc gamma RII subtypes were initially recognized by the failure of T cells from 40% of individuals to proliferate in response to mAb Leu 4 (mouse IgG1, anti-CD3), a response that requires the binding of the Fc region of the Leu 4 mAb to Fc gamma RII on monocyte accessory cells. Inas-much as mouse IgG1, does not bind efficiently to the nonresponder form of Fc gamma RII, mAb Leu 4 is unable to induce proliferation in these individuals. IEF data on Fc gamma RII from Leu 4 responder and nonresponder individuals suggested that the structural gene for Fc gamma RII consisted of two allelic forms R (responder) and N (nonresponder) producing the phenotypes RR, RN, and NN. Thus, exclusive expression of the nonresponder allele in monocytes of "nonresponder" individuals, appeared to be responsible for the lack of proliferation observed. In cooperation with the IVth International Conference on Human Leukocyte Differentiation Antigens, we analyzed CDw32 mAb to determine if they could distinguish the responder and nonresponder forms of Fc gamma RII. We report that mAb 41H16 binds preferentially to the responder allotypic form of Fc gamma RII expressed on human monocytes. When quantitative flow cytometry is used to measure the binding of both mAb 41H16 (responder Fc gamma RII) and mAb IV.3 (all myeloid cell Fc gamma RII), we are able to subdivide the responder population into homozygous and heterozygous responders. In addition, mAb 41H16 blocks the binding of mAb IV.3 to monocytes and inhibits proliferation when added to cells before addition of mAb Leu 4. We also show that polymorphonuclear leukocytes and platelets have the same allotypic differences in the binding of 41H16 as do monocytes. However, a subset of lymphocytes (previously shown to be B cells) expresses the 41H16 epitope with no evidence for donor to donor variability.

The monoclonal antibody 41H16 detects the Leu 4 responder form of human Fc gamma RII

Human FcR for IgG can be divided into three classes (Fc gamma RI, II, and III) based on their structure and reactivity with mAb. Fc gamma RII can be further subdivided into two categories based on functional and biochemical assays. These two Fc gamma RII subtypes were initially recognized by the failure of T cells from 40% of individuals to proliferate in response to mAb Leu 4 (mouse IgG1, anti-CD3), a response that requires the binding of the Fc region of the Leu 4 mAb to Fc gamma RII on monocyte accessory cells. Inas-much as mouse IgG1, does not bind efficiently to the nonresponder form of Fc gamma RII, mAb Leu 4 is unable to induce proliferation in these individuals. IEF data on Fc gamma RII from Leu 4 responder and nonresponder individuals suggested that the structural gene for Fc gamma RII consisted of two allelic forms R (responder) and N (nonresponder) producing the phenotypes RR, RN, and NN. Thus, exclusive expression of the nonresponder allele in monocytes of "nonresponder" individuals, appeared to be responsible for the lack of proliferation observed. In cooperation with the IVth International Conference on Human Leukocyte Differentiation Antigens, we analyzed CDw32 mAb to determine if they could distinguish the responder and nonresponder forms of Fc gamma RII. We report that mAb 41H16 binds preferentially to the responder allotypic form of Fc gamma RII expressed on human monocytes. When quantitative flow cytometry is used to measure the binding of both mAb 41H16 (responder Fc gamma RII) and mAb IV.3 (all myeloid cell Fc gamma RII), we are able to subdivide the responder population into homozygous and heterozygous responders. In addition, mAb 41H16 blocks the binding of mAb IV.3 to monocytes and inhibits proliferation when added to cells before addition of mAb Leu 4. We also show that polymorphonuclear leukocytes and platelets have the same allotypic differences in the binding of 41H16 as do monocytes. However, a subset of lymphocytes (previously shown to be B cells) expresses the 41H16 epitope with no evidence for donor to donor variability.

Characterization of antigen processing and presentation by resting B lymphocytes

The production of antibody to a thymus-dependent Ag requires cooperation between the B cell and an Ag-specific Th cell. MHC restriction of this interaction implies that the Th cell recognizes Ag on the B cell surface in the context of MHC molecules and that the Ag-specific B cell gets help by acting as an APC for the Th cell. However, a number of studies have suggested that normal resting B cells are ineffective as APC, implying that the B cell must leave the resting state before it can interact specifically with a Th cell. Other studies, including our own with rabbit globulin-specific mouse T cell lines and hybridomas, show that certain T cell lines can be efficiently stimulated by normal resting B cells. One possible explanation for the above contradiction is that our B cells have become activated before presentation. Here we show that presentation by size-selected small B cells is not the result of nonspecific activation signals generated by the T cells or components of the medium. Also, although LPS activation does increase the efficiency of presentation by small B cells, use of large cells in place of small cells or preincubation of resting B cells with mitogenic doses of anti-Ig does not. Another possibility that we considered was that small B cells are unable to process Ag and that we had selected T cell lines that were capable of recognizing native Ag on the B cell surface. In the majority of cases, experiments with B cell lines and macrophages have shown that Ag presentation requires Ag processing, a sequence of events that includes internalization of Ag into an acid compartment, denaturation or digestion of Ag into fragments, and its return to the cell surface in the context of class II MHC molecules. The experiments reported here show that our T cell lines require an Ag processing step and that small resting B cells, like other APC, process Ag before presenting it to T cells. Specifically, we show that an incubation of 2 to 4 h is required after the Ag pulse before Ag presentation becomes resistant to irradiation. Shortly after the pulse, the Ag enters a pronase-resistant compartment. Although efficient Ag presentation requires initial binding to membrane Ig, Ag is no longer associated with membrane Ig at the time of presentation and is not presented in its intact form, because removal of membrane Ig by goat anti-Ig blocks presentation before but not after the Ag pulse.

Characterization of antigen processing and presentation by resting B lymphocytes

The production of antibody to a thymus-dependent Ag requires cooperation between the B cell and an Ag-specific Th cell. MHC restriction of this interaction implies that the Th cell recognizes Ag on the B cell surface in the context of MHC molecules and that the Ag-specific B cell gets help by acting as an APC for the Th cell. However, a number of studies have suggested that normal resting B cells are ineffective as APC, implying that the B cell must leave the resting state before it can interact specifically with a Th cell. Other studies, including our own with rabbit globulin-specific mouse T cell lines and hybridomas, show that certain T cell lines can be efficiently stimulated by normal resting B cells. One possible explanation for the above contradiction is that our B cells have become activated before presentation. Here we show that presentation by size-selected small B cells is not the result of nonspecific activation signals generated by the T cells or components of the medium. Also, although LPS activation does increase the efficiency of presentation by small B cells, use of large cells in place of small cells or preincubation of resting B cells with mitogenic doses of anti-Ig does not. Another possibility that we considered was that small B cells are unable to process Ag and that we had selected T cell lines that were capable of recognizing native Ag on the B cell surface. In the majority of cases, experiments with B cell lines and macrophages have shown that Ag presentation requires Ag processing, a sequence of events that includes internalization of Ag into an acid compartment, denaturation or digestion of Ag into fragments, and its return to the cell surface in the context of class II MHC molecules. The experiments reported here show that our T cell lines require an Ag processing step and that small resting B cells, like other APC, process Ag before presenting it to T cells. Specifically, we show that an incubation of 2 to 4 h is required after the Ag pulse before Ag presentation becomes resistant to irradiation. Shortly after the pulse, the Ag enters a pronase-resistant compartment. Although efficient Ag presentation requires initial binding to membrane Ig, Ag is no longer associated with membrane Ig at the time of presentation and is not presented in its intact form, because removal of membrane Ig by goat anti-Ig blocks presentation before but not after the Ag pulse.

Immunocytochemistry: its evolution and criteria for its application in the study of epon-embedded cells and tissue

The word immunocytochemistry is currently used to describe a number of methods that can be employed to localize antigens within cells by means of antigen-specific antibodies. In this article we will review a number of these methods, including immunofluorescence, immunoperoxidase, avidin-biotin, and colloidal-gold techniques. The advantages and disadvantages of the various methods are discussed, special attention being focused upon immunocytochemical staining of plastic-embedded tissue. Studies on the light microscope level show that embedding tissue in plastic prior to immunoperoxidase staining not only improves visualization of antigen-specific staining but also provides an accurate and efficient means of prescreening tissue for antigen prior to immunocytochemical staining on the electron microscope level. Varying section thickness between 1 and 3 microns does not significantly influence staining, whereas the fixative used to preserve the tissue under study does. On the electron microscope level, the colloidal gold technique appears superior to immunoperoxidase staining. It is both esthetically more pleasing and highly sensitive. Of five different colloidal gold methods tested, the most sensitive is the two-step technique that employs an antigen-specific primary antibody followed by a gold-labeled secondary antibody. Throughout this article, special emphasis is placed on the use of proper controls, both on the light and electron microscope levels. Where possible, such controls should include substitution of specific antiserum with normal serum; the use of antigen-adsorbed antiserum; the use of antisera with specificities for antigens not present in the tissue being studied; the use of tissue previously shown to be stainable for the antigen; and if cultured cells are being studied, the use of a number of cell types that do not contain the antigen.

Immunocytochemical staining of cytocentrifuge prepared cultured cells: nonspecific staining and its elimination

In an attempt to localize hormones in cytocentrifuge-prepared cultured cells of small cell carcinoma of the lung (SCCL), various modifications of the immunoperoxidase (PAP) procedure (Sternberger, 1979) were tested. When using glutaraldehyde, formaldehyde, or p-benzoquinone fixation (Pearse & Polak, 1975) and rabbit antibodies in primary or bridging steps of the PAP procedure, nonspecific staining (false positives) could be elicited with the majority of rabbit antibodies tested, but not with antibodies from other animal sources. This problem could be eliminated by fixation of cells either with formalin-acetone (Mason et al., 1975) or, when using antibodies from a source other than rabbit, glutaraldehyde. It was not possible to localize ACTH in DMS-79, a human SCCL line known to produce this hormone. However, calcitonin was localized in the calcitonin-producing SCCL line DMS-53. Failure to localize ACTH in DMS-79 may be due to the lower levels of this hormone in DMS-79, as compared to the levels of calcitonin in DMS-53. This study emphasizes the importance of proper controls before concluding successful localization in a given immunocytochemical preparation of cultured cells.

Unlabeled antibody methods in electron microscopy: a comparison of single and multistep procedures using colloidal gold

A comparative study of five unlabeled antibody methods was conducted on the electron microscopic level using bridging techniques and colloidal gold. The study was based on the principles of the single-step colloidal gold (GLAD) method (Larsson L: Nature 282:743, 1979) and the multistep single- and double-bridge techniques used in postembedding immunoperoxidase procedures (PAP) (Sternberger LA: Immunocytochemistry, 2nd ed. Wiley, New York, 1979). Using medullary thyroid carcinoma and the same lot of primary antiserum (goat anti-calcitonin) for each procedure, it was shown that adequate localization of calcitonin with the single-step GLAD method was attainable only at dilutions of 1:100 or lower. The single-bridge technique using goat anti-calcitonin, sheep anti-goat immunoglobulin (Ig)G, and goat anti-calcitonin and antigen-coated gold, respectively, worked well at dilutions of up to 1:5000 but not at dilutions of 1:10,000, while single- and double-bridging techniques utilizing goat anti-calcitonin, sheep (Sh) anti-goat IgG, and sheep anti-goat IgG-coated gold produced good localization at a 1:10,000 dilution of primary antiserum. A two-step method using goat anti-calcitonin and sheep anti-goat IgG-coated gold, respectively, appeared to be the most sensitive technique, with adequate antigen localization occurring at a dilution of 1:25,000. While in our hands the two-step method appeared superior in sensitivity to the single-bridge IgG-coated gold technique, each method has its own advantages depending on the individual needs of the researcher.

Bombesin and calcitonin secretion by pulmonary carcinoma is modulated by cholinergic receptors

Three established cell lines derived from human small cell carcinoma of the lung, and known to produce significant amounts of peptide hormones were used to evaluate the regulation of hormone secretion by cholinergic agonists. In two of the cell lines (DMS 53, DMS 153) acetylcholine chloride, bethanechol chloride, and carbamylcholine at the concentrations of 10(-3)M to 10(-5)M stimulated secretion of bombesin and calcitonin as measured by RIA. The third cell line, DMS 406, was not significantly stimulated. Inhibition of induced stimulation by the cholinergic antagonist atropine, but not hexamethonium, indicated the presence of muscarinic rather than the nicotinic type of cholinergic receptors on the stimulatable cells. These receptors appear to mediate hormone secretion comparably to normal endocrine cells.

Audiologic and metabolic findings in 90 patients with fluctuant hearing loss

Fluctuant hearing loss is a common occurrence. It is difficult to diagnose in its early stages when hearing thresholds are near normal and the only complaints the patient has are of fullness and tinnitus. Audiologic tests are helpful in confirming the diagnosis. Impedance measurements are an accurate assessment of middle ear status and can assist in localizing the fullness experienced by these patients. Site of lesion tests and discrimination scores at various sensation levels are sensitive indexes of disease activity. Observations during medical treatment of 90 patients with metabolic dysfunction (hyperlipoproteinemia: hypoglycemia; hypothyroidism) suggest that discrimination scores fluctuate more widely than do pure tone thresholds over a period of time. Thirty patients were given complete audiologic testing after dietary management and treatment. All reported relief from tinnitus and fullness, and 15 or 50% showed improved audiograms and discrimination scores. Any change in the energy reserve or metabolic rate of the inner ear by a systemic metabolic dysfunction can contribute to or cause sensorineural hearing loss. Energy flow from metabolic sources is needed to transduce the acoustic stimuli into neural excitation patterns. The presence of any systemic metabolic dysfunction can be expected to contribute to and cause fluctuant hearing loss.