A sensitive immunochemical assay for biologically active MuIFN-gamma

Measurement of antiviral activity induced by interferons alpha, beta, and gamma

The Basic Protocol in this unit describes an assay for murine IFN-induced antiviral activity and employs vesicular stomatitis virus (VSV) and IFN-sensitive fibroblasts. Support Protocol describes the preparation of VSV cultures and the calculation of multiplicity of infection (MOI; i.e., concentration of viral particles required to infect cells). Support Protocol describes the antibody neutralization assay, which can be used to identify the bioactive species of IFN in a sample, or to test the potency of an antibody preparation against a particular species of IFN. Alternate Protocol 1 covers measurement of human IFN-induced antiviral activity; while the steps are quite similar to Basic Protocol, different viral and cell cultures are described.

Immune response measured in human volunteers vaccinated with autoclaved Leishmania major vaccine mixed with low dose of BCG

The immune responses induced against Leishmania antigens in volunteers who were vaccinated in a double-blind, randomized field efficacy trial of a preparation of autoclaved Leishmania major (ALM) mixed with a low dose of Bacille Calmette-Guerin vaccine (BCG) who developed either a cutaneous leishmaniasis (CL) lesion due to exposure to infected sandfly bite(s) or did not develop a lesion during the course of the trial were studied and compared with those of non-vaccinated controls. Blood samples were also assayed from different groups including volunteers with history of CL and volunteers with previous positive or negative leishmanin skin test (LST) without a history of CL. The vaccinated volunteers had received a single dose of either ALM mixed with a low dose of BCG or the same dose of BCG alone. The LST and in vitro proliferative response (stimulation index, SI), interferon gamma (IFN-gamma) production and, in a few cases, interleukin (IL)-4 production of peripheral blood mononuclear cells to soluble Leishmania antigens were measured. The results indicated that volunteers who developed CL in the vaccine arm showed a slightly higher SI than cases who received BCG alone. Volunteers with history of CL and volunteers with positive LST demonstrated the strongest proliferation indices and IFN-gamma production. The data suggest that a single dose of ALM + BCG induces a weak Th1 response in vaccinated volunteers that is far lower than that in volunteers with prior subclinical infection or volunteers with history of CL, who are presumed to be immune.

Propolis: lymphocyte proliferation and IFN-gamma production

We evaluated propolis influence on polyclonal activation of lymphocytes by concanavalin A (Con A). The in vitro experiments showed that propolis decreases splenocyte proliferation both in the absence or presence of Con A. The suppression in mitogen-induced splenocyte proliferation also occurred when mice were treated intraperitoneally with propolis for 3 days. An increased of IFN-gamma production in the culture supernatants of the same cells was observed. A dual action of propolis on lymphocyte activation was proposed: it decreases splenocyte proliferation in the presence or absence of Con A and stimulates IFN-gamma production by spleen cells. These results are important to understand the immunomodulatory action of propolis on the host's specific and non-specific immunity.

Lack of C3 affects Th2 response development and the sequelae of chemotherapy in schistosomiasis

The role of the third component of complement (C3) during schistosome infection was investigated using mice deficient in C3. While no effect was observed 8 wk after infection on worm development or liver pathology, Ag-specific Th2-associated cytokine production (IL-13, IL-5, IL-6, and IL-10) was significantly reduced, and IFN-gamma production was enhanced in the absence of C3. IgG1 and IgE, but not IgG2a or IgM, Ab responses were also significantly impaired in infected C3(-/-) mice, suggesting that C3 may play a role in IL-4-mediated Th2 response enhancement during schistosome infection. Furthermore, C3-deficient mice could not effectively clear adult worms after praziquantel (PZQ) treatment and suffered increased morbidity due to the overproduction of proinflammatory mediators following drug administration. However, the ischemic liver damage that normally accompanies PZQ administration in infected wild-type mice was substantially reduced in treated C3-deficient mice, probably due to the absence of dead or dying worms in the livers of these animals. Together these results indicate that C3 enhances Th2 responses during schistosome infection, potentiates PZQ-mediated parasite clearance, and reduces chemotherapy-induced proinflammatory mediator production.

The function of gamma interferon-inducible GTP-binding protein IGTP in host resistance to Toxoplasma gondii is Stat1 dependent and requires expression in both hematopoietic and nonhematopoietic cellular compartments

IGTP is a member of the 47-kDa family of gamma interferon (IFN-gamma)-induced GTPases. We have previously shown that IGTP is critical for host resistance to Toxoplasma gondii infection. In the present study, we demonstrate that T. gondii-induced IGTP expression in vivo and IFN-gamma-driven synthesis of the protein in vitro are dependent on Stat1. Consistent with this observation, Stat1-deficient animals succumbed to T. gondii infection with the same rapid kinetics as IGTP(-/-) mice. To ascertain the cellular levels at which IGTP functions in host control of acute infection, we constructed reciprocal bone marrow chimeras between IGTP-deficient and wild-type mice. Resistance to infection was observed only when IGTP was present in both hematopoietic and nonhematopoietic compartments. To assess the possible contribution of IGTP to the maintenance of parasite latency, partial chemotherapy was used to allow the establishment of chronic infection in IGTP-deficient animals. Upon cessation of drug treatment, these animals showed delayed mortality compared with similarly infected and treated IFN-gamma-deficient or inducible nitric oxide synthase-deficient mice, which succumbed rapidly. Parallel experiments performed with drug-treated bone marrow chimeras supported a role for the hematopoietic compartment in this NO-dependent, IGTP-independent control of chronic infection. Taken together, our findings demonstrate that host resistance mediated by IGTP is a Stat1-induced function which in the case of T. gondii acts predominantly to restrict acute as opposed to chronic infection. This effector mechanism requires expression of IGTP in cells of both hematopoietic and nonhematopoietic origin. In contrast, in latent infection, hematopoietically derived cells mediate resistance by means of a largely NO-dependent pathway.

Schistosomiasis delays lesion resolution during Leishmania major infection by impairing parasite killing by macrophages

Infection of mice with Schistosoma mansoni delays the resolution of cutaneous lesions and parasitaemia during Leishmania major infection. In contrast, L. major infection does not appear to alter the course of schistosomiasis. Analysis of the cytokine responses in the draining lymph nodes (LN) indicates that, while L. major infection had no effect on schistosome-specific interleukin (IL)-4 production by mesenteric LN (MLN) cells, coinfection with S. mansoni resulted in decreased leishmania-induced interferon (IFN)-gamma, tumour necrosis factor-alpha and nitric oxide production by popliteal LN (PLN) cells 4 weeks after L. major infection. In addition, PLN cells produced higher levels of IL-4 4 weeks after L. major infection in coinfected mice. Finally, IFN-gamma-stimulated macrophages isolated from S. mansoni-infected mice were impaired in their ability to kill L. major after in vitro infection. These results suggest that pre-existence of a strong Th2 response-dominated infection can alter the responses to Th1-inducing pathogens at peripheral sites and impair Th1-mediated effector functions.

Role of gamma interferon in the pathogenesis of severe schistosomiasis in interleukin-4-deficient mice

In the absence of interleukin-4 (IL-4), infection with Schistosoma mansoni leads to a severe fatal disease rather than the chronic survivable condition that occurs in wild-type (WT) mice. Because the sustained production of NO most closely correlates to weight loss and fatality in infected IL-4(-/-) mice and because gamma interferon (IFN-gamma) is an important inducer of inducible NO synthase, infected IL-4(-/-) mice were treated with anti-IFN-gamma antibodies to determine the role of IFN-gamma during schistosomiasis in WT and IL-4(-/-) animals. When IFN-gamma was neutralized, Th2 responses were enhanced and NO production was reduced in both WT and IL-4(-/-) mice. The decreased NO production correlated with a rescue of proliferation in splenocytes from infected IL-4(-/-) mice. Furthermore, the neutralization of IFN-gamma in vivo improved the gross appearance of the liver and led to a reduction in granuloma size in infected IL-4(-/-) but not WT mice. However, the neutralization of IFN-gamma in vivo did not affect the development of severe disease in infected IL-4(-/-) mice. These results suggest that while the increased production of IFN-gamma does lead to some of the pathology observed in infected IL-4(-/-) mice, it is not ultimately responsible for cachexia and death.

Evaluation of a recombinant Listeria monocytogenes expressing an HIV protein that protects mice against viral challenge

Vaccine strategies that utilize cell mediated immunity to control infection will be a necessary component of human immunodeficiency virus (HIV) vaccines. In previous studies we have shown that a Listeria monocytogenes recombinant expressing HIV-Gag elicits strong CD8+ and CD4+ T cell responses against HIV Gag in addition to its own secreted proteins. Here, we show that Lm-Gag can protect mice against a viral challenge with a recombinant vaccinia virus expressing Gag, in an antigen specific manner, and that this protection is T cell mediated. These results further support the use of L. monocytogenes as a vaccine approach for HIV through the induction of T cell immunity.

Different Leishmania species determine distinct profiles of immune and histopathological responses in CBA mice

Most experimental studies on leishmaniasis compare two different inbred strains of mice that are resistant or susceptible to one species of Leishmania. In the present study we characterized some cytokines and nitric oxide production as well as histological changes related to resistance and susceptibility in isogenic CBA mice infected with Leishmania major or Leishmania amazonensis. CBA mice are capable of controlling infection with L. major, but they succumb to infection with L. amazonensis. Cells from susceptible L. amazonensis-infected CBA mice produced interleukin (IL)-4 and IL-10 but no interferon (IFN)-gamma. On the other hand, resistant L. major-infected CBA mice produced IFN-gamma and IL-10, but IL-4 was detected only in the first week of infection. Histopathological studies showed patterns of tissue responses at the site of the infection and in the draining lymph nodes that correlated with resistance or susceptibility. Resistant mice showed a mixed inflammatory cell infiltration and granulomas in the lesions, whereas in susceptible mice only heavily parasitized macrophages were seen. Our results indicate an important role of the parasite species in determining the pattern of immune response. L. amazonensis induces a Th2-type immune response, whereas L. major induces a Th1-type response. These factors must be identified and taken into account in the strategies for the development of vaccines against leishmaniasis. The model presented here will be useful for the study of such factors.

Th1 T Cell Responses to HIV-1 Gag Protein Delivered by a Listeria monocytogenes Vaccine Are Similar to Those Induced by Endogenous Listerial Antigens

Listeria monocytogenes is a facultative intracellular bacterium that lives and grows in the cytoplasm of the host cell. The hallmark of a listerial infection is a cell-mediated immune response to its own secreted virulence factors. Thus, L. monocytogenes vaccines engineered to secrete HIV proteins may be ideal vectors for boosting cellular immune responses against HIV. Using strains of L. monocytogenes that stably express and secrete HIV Gag (Lm-Gag) to deliver this Ag to the immune system, we have previously shown strong MHC class I-restricted cytotoxic T cell responses to this protein. In this study, we examine MHC class II-restricted T cell responses to HIV-Gag delivered by Lm-Gag. We demonstrate the induction of CD4+ T cells that are HIV-Gag specific and identify three epitopes in two strains of mice, BALB/c (H-2d) and C57BL/6 (H-2b), two of which are both H-2d and H-2b restricted, but are not immunodominant for both haplotypes. In addition, we show that the CD4+ T cells induced are of the Th1 phenotype that produce IFN-γ at levels similar to CD4+ T cells induced to endogenous listerial Ags. These studies suggest that chromosomally modified strains of L. monocytogenes may be useful as vaccine vectors for the induction of Th1 T cell responses against HIV.

Immunostimulatory oligodeoxynucleotides promote protective immunity and provide systemic therapy for leishmaniasis via IL-12- and IFN-gamma-dependent mechanisms

Resistance to murine leishmaniasis correlates with development of a CD4(+) T helper 1 (Th1)-predominant immune response. To determine whether immunostimulatory CpG-containing oligodeoxynucleotides (CpG-ODN), known to promote a Th1 immune response, could provide protection from Leishmania infection, CpG-ODN and freeze-thawed (F/T) Leishmania major were coinjected intradermally into susceptible BALB/c mice. A Leishmania-specific Th1-predominant immune response was induced, and 40% of animals were protected from subsequent challenge with infectious organisms, with 0% protection of animals injected with F/T Leishmania organisms and PBS, F/T organisms and control ODN, or F/T organisms alone. More striking protection (65-95%) was seen in mice first infected with intact Leishmania organisms and then injected with CpG-ODN, either at the site of infection or at a remote site. To determine whether the therapeutic protection provided by CpG-ODN depended on IL-12 and IFN-gamma production, both IFN-gamma-deficient BALB/c mice and BALB/c mice treated with neutralizing anti-IL-12 mAb were first inoculated with Leishmania and then treated with either CpG-ODN, ODN, or PBS. None of these IFN-gamma-deficient mice survived (0/20, 0/20, and 0/20 respectively). Furthermore, neutralization of IL-12 completely abolished the therapeutic protection provided by CpG-ODN (0/20 mice surviving). We conclude that immunostimulatory DNA sequences likely exert systemic effects via IL-12 and IFN-gamma-dependent mechanisms and hold considerable promise as both vaccine adjuvants and potential therapeutic agents in the prevention and treatment of leishmaniasis.

IL-4- and IL-4 Receptor-Deficient BALB/c Mice Reveal Differences in Susceptibility to Leishmania major Parasite Substrains

Using genetically pure BALB/c mice deficient in IL-4 (IL-4−/−) or IL-4 receptor α-chain (IL-4Rα−/−), we have observed different disease outcomes to Leishmania major infection depending on the parasite substrain. Infection with L. major LV39 caused progressive, nonhealing ulcers and uncontrolled parasite growth in both IL-4−/− and IL-4Rα−/− mice. In contrast, infection with L. major IR173 was partially controlled in IL-4−/− mice but efficiently controlled in IL-4Rα−/− mice. Both IL-4−/− and IL-4Rα−/− mice infected with either substrain displayed reduced Th2 responses. Surprisingly, IFN-γ secretion was not up-regulated in the mutant mice, even in the IL-4Rα−/− mice, which were resistant to L. major IR173. The lack of increased IFN-γ production suggests that cytokine cross-regulation may not be operating in this model and that the effective ratios of Th1/Th2 cytokines become more indicative of disease outcome. The partial vs complete resistance to IR173 in IL-4−/− or IL-4Rα−/− mice implies that, in addition to IL-4, IL-13 may be involved in disease progression during L. major infection. The results with LV39 infection indicate that yet another unidentified factor is capable of causing susceptibility to L. major in the absence of IL-4 or IL-4 signaling.

The Absence of IL-6 Does Not Affect Th2 Cell Development In Vivo, But Does Lead to Impaired Proliferation, IL-2 Receptor Expression, and B Cell Responses

The role of IL-6 in Th2 cell differentiation and response development after the injection of eggs from Schistosoma mansoni was investigated using wild-type (WT) and IL-6−/− mice. IL-6 was induced in the lymph nodes (LN) of WT mice within 24 h of egg injection, and IL-4 production by WT LN cells and CD4 T cells isolated 24 h after egg injection and stimulated in vitro was observed. In the absence of IL-6, this early production of IL-4 by LN cells and purified CD4 T cells was not abolished; although the level of IL-4 produced by IL-6−/− LN cells was similar to WT, IL-4 production by purified IL-6−/− CD4 T cells was reduced compared with WT. Despite the difference in CD4 T cell production of IL-4, the development of egg-specific Th2 cells 7 days after egg injection was not affected by the absence of IL-6. Nevertheless, Ab production was impaired and the in vitro proliferative response of whole LN cell populations, CD4 and CD8 T cells, and B cells from IL-6−/− mice was poor compared with WT. The proliferative defect in the IL-6−/− cells correlated with decreased IL-2R expression, and addition of exogenous IL-6 enhanced IL-2R expression as well as proliferation of LN cells from IL-6−/− mice. These studies demonstrate that Th2 differentiation and response development in vivo is not dependent on IL-6, but that Th-dependent and independent B cell responses are. Our results also emphasize the importance of IL-6 for lymphoproliferation, possibly through induction of IL-2R expression.

Role of endogenous tumor necrosis factor alpha and gamma interferon in resistance to Corynebacterium pseudotuberculosis infection in mice

The production and roles of endogenous tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma) in the infection of Corynebacterium (C.) pseudotuberculosis were investigated in mice. The maximum levels of TNF-alpha and IFN-gamma were detected on day 4 after infection. The administration of anti-TNF-alpha monoclonal antibody (mAb) as well as anti-IFN-gamma mAb increased bacterial proliferation in the organs, leading to the death of infected mice, but anti-IFN-gamma mAb showed a less marked effect than anti-TNF-alpha mAb. The suppressive effect of anti-TNF-alpha and anti-IFN-gamma mAbs on anticorynebacterial resistance was augmented by the simultaneous administration of these antibodies. Anti-TNF-alpha mAb was found to be highly effective when administered on day 0 and day 4, suggesting that TNF-alpha produced during the early stage of infection is critical for the generation of resistance. Histologically, many microabscesses, severe follicular swelling and lymphocyte destruction were observed in mice treated with anti-TNF-alpha or anti-IFN-gamma mAb. Injection of anti-CD4 or anti-CD8 mAb also resulted in significantly increased mortality and a marked suppression of IFN-gamma production, but had no effect on TNF-alpha production. Carrageenan also showed a marked effect on the exacerbation of infection. Taken together, these results suggest that endogenously produced TNF-alpha and IFN-gamma are both essential to the host defense against C. pseudotuberculosis infection and that these cytokines may have an additive effect.

Atypical pulmonary eosinophilia is mediated by a specific amino acid sequence of the attachment (G) protein of respiratory syncytial virus

We analyzed the immune responses evoked by a series of overlapping peptides to better understand the molecular basis for respiratory syncytial virus (RSV) G protein-induced eosinophilia in BALB/c mice. In vitro stimulation of spleen cells from natural G protein-primed mice showed dominant proliferative and cytokine (interferon [IFN]-gamma and interleukin [IL]-5) responses to a peptide encompassing amino acids 184-198. Mice vaccinated with peptide 184- 198 conjugated to keyhole limpet hemocyanin showed significant pulmonary eosinophilia (39.5%) after challenge with live RSV. In contrast, mice immunized with a peptide (208-222) conjugate associated with induction of IFN-gamma secreting spleen cells did not exhibit pulmonary eosinophilia after challenge. The in vivo depletion of CD4(+) cells abrogated pulmonary eosinophilia in mice vaccinated with the peptide 184-198 conjugate, whereas the depletion of CD8(+) cells had a negligible effect. Therefore, we have identified an association between peptide 184- 198 of natural G protein and the CD4(+) T cell-mediated induction of pulmonary eosinophilia after live RSV challenge. Out of 43 human donors, 6 provided peripheral blood mononuclear cells that showed reactivity to G protein from RSV A2, 3 of which responded to peptide 184- 198. The results have important implications for the development of a vaccine against RSV.

Genetic immunization with glycoprotein 63 cDNA results in a helper T cell type 1 immune response and protection in a murine model of leishmaniasis

Genetic immunization is a promising gene therapy approach for the prevention and treatment of infectious disease. Plasmid DNA expressing genes of pathogens is directly introduced into host cells and specific cell-mediated and/or humoral immune responses are elicited against the encoded protein. Leishmaniasis is a significant world-wide health problem for which no vaccine exists. In susceptible animals, such as BALB/c mice, protection from leishmaniasis requires induction of a Thl immune response. In this study, cell-mediated immunity to Leishmania major (L. major) was induced by injecting BALB/c mice intradermally with plasmid DNA expressing the conserved L. major cell surface glycoprotein gp63 (gp63-pcDNA-3). CD4 T lymphocytes from gp63-pcDNA-3-immunized mice proliferated and produced IFN-gamma (but not IL-4) when stimulated in vitro with freeze-thawed parasites, consistent with a Th1 immune response. In contrast, lymphocyte proliferation in animals immunized with freeze-thawed parasites was associated with IL-4 (but not IFN-gamma) production, suggesting a nonprotective Th2 response. Challenge studies revealed that gp63-pcDNA-3 vaccination protected 30% of susceptible mice (21 of 70) from Leishmania infection while neither gp63 protein (0 of 20) nor freeze-thawed parasite vaccines (0 of 50) were efficacious. Dendritic cells derived from skin of gp63-pcDNA-3-injected mice also immunized naive recipients and protected them from leishmaniasis. We conclude that gp63-pcDNA-3 genetic vaccination results in a CD4-dependent Th1 immune response that correlates with protection from disease, and suggest that skin-derived dendritic cells are involved in priming this response.

Saliva of Rhipicephalus sanguineus tick impairs T cell proliferation and IFN-gamma-induced macrophage microbicidal activity

In this study, we investigated tick saliva effects on T cell proliferation, antigen presentation and IFN-gamma-induced macrophage activation, events which are associated with host immune defense mechanisms. Mice repeatedly infested with Rhipicephalus sanguineus ticks, similarly to dogs, did not develop resistance to further infestations. We determined that R. sanguineus tick saliva inhibited, in a dose-dependent manner, both Con-A and specific antigen-induced splenic T cell proliferation. Tick saliva diluted twenty times (64 microg/ml) inhibited Con-A-induced and antigen-specific T cell proliferation in 83% and 69%, respectively. In addition, the inhibition of cell proliferation correlated with a decrease in IL-2 production. Microconcentrator fractionated saliva was tested on a Con-A-induced cell proliferation assay, and showed that one fraction between 3 and 10 kDa and another smaller than 3 kDa can be responsible for the inhibition of T cell proliferation. Although saliva inhibited cell proliferation, it did not impair antigen presentation. Tick saliva further abrogated the killing of intracellular forms of Trypanosoma cruzi by IFN-gamma-activated macrophages. Moreover, saliva-induced macrophage inhibition of IFN-gamma-induced-trypanocidal activity was paralleled with 69% less nitric oxide (NO) production. Finally, tick saliva doubled the production of IL-10 and reduced 84.6% production of IFN-gamma by splenocytes cultured with T. cruzi, suggesting that decreased macrophage NO production may be due to a saliva-induced cytokine imbalance, leading to decreased NO synthase activity. Together, these data indicate that tick saliva can modulate host immune response, thus, contributing to its feeding success and favoring the transmission of tick-borne pathogens.

Differential Activation of T Cells by Natural Antigen Peptide Analogues: Influence on Autoimmune and Alloimmune In Vivo T Cell Responses

Recent studies using synthetic altered peptide ligands (Analogues) have led to the fine dissection of TCR-mediated T cell functions elicited by Ag recognition. Certain Analogues behave as full agonists of the antigenic peptide while others are partial agonists in that they only trigger selected T cell functions. Additionally, peptide Analogues can behave as antagonists by inhibiting functions of T cell clones when coincubated with the wild-type peptide. In fetal thymic organ cultures, synthetic altered peptide ligands can impact T cell repertoire selection. However, the influence of naturally occurring peptide Analogues on T cell immunity in vivo remains hypothetical. We previously reported that, in B10.A mice, immunogenicity and tolerogenicity of the self-MHC class I peptide, Ld 61-80, were influenced by the presentation of a cross-reactive self-peptide, Kk 61-80. Here, we show that Kk 61-80 self-peptide represents a partial agonist of Ld 61-80 in that it induced the proliferation but not the lymphokine production of Ld 61-80-primed T cells. Next, we showed that presentation of Kk 61-80 Analogue peptide mediated T cell tolerance toward Ld 61-80 self-peptide. Alternatively, when Ld protein represented an alloantigen displayed on transplanted cells, immunization with Kk 61-80 Analogue sensitized recipient mice to Ld 61-80 peptide, thus inducing potent immune responses to donor cells. These results show that the presentation of natural Analogue peptides may represent an essential component of T cell responses involved in autoimmunity and transplant rejection.

Interferon consensus sequence binding protein-deficient mice display impaired resistance to intracellular infection due to a primary defect in interleukin 12 p40 induction

Mice lacking the transcription factor interferon consensus sequence binding protein (ICSBP), a member of the interferon regulatory factor family of transcription proteins, were infected with the intracellular protozoan, Toxoplasma gondii. ICSBP-deficient mice exhibited unchecked parasite replication in vivo and rapidly succumbed within 14 d after inoculation with an avirulent Toxoplasma strain. In contrast, few intracellular parasites were observed in wild-type littermates and these animals survived for at least 60 d after infection. Analysis of cytokine synthesis in vitro and in vivo revealed a major deficiency in the expression of both interferon (IFN)-gamma and interleukin (IL)-12 p40 in the T. gondii exposed ICSBP-/- animals. In related experiments, macrophages from uninfected ICSBP-/- mice were shown to display a selective impairment in the mRNA expression of IL-12 p40 but not IL-1alpha, IL-1beta, IL-1Ra, IL-6, IL-10, or TNF-alpha in response to live parasites, parasite antigen, lipopolysaccharide, or Staphylococcus aureus. This selective defect in IL-12 p40 production was observed regardless of whether the macrophages had been primed with IFN-gamma. We hypothesize that the impaired synthesis of IL-12 p40 in ICSBP-/- animals is the primary lesion responsible for the loss in resistance to T. gondii because IFN-gamma-induced parasite killing was unimpaired in vitro and, more importantly, administration of exogenous IL-12 in vivo significantly prolonged survival of the infected mice. Together these findings implicate ICSBP as a major transcription factor which directly or indirectly regulates IL-12 p40 gene activation and, as a consequence, IFN-gamma-dependent host resistance.

An interleukin 4 (IL-4)-independent pathway for CD4+ T cell IL-4 production is revealed in IL-4 receptor-deficient mice

IL-4 receptor alpha chain (IL-4Ralpha)-deficient mice were generated by gene-targeting in BALB/c embryonic stem cells. Mutant mice showed a loss of IL-4 signal transduction and functional activity. The lack of IL-4Ralpha resulted in markedly diminished, but not absent, TH2 responses after infection with the helminthic parasite Nippostrongylus brasiliensis. CD4+, CD62L-high, and CD62L-low T cell populations from uninfected IL-4Ralpha-/- mice were isolated by cell sorting. Upon primary stimulation by T cell receptor cross-linkage, the CD62L-low, but not the CD62L-high, cells secreted considerable amounts of IL-4, which was strikingly enhanced upon 4-day culture with anti-CD3 in the presence or absence of IL-4. CD62L-low cells isolated from IL-4Ralpha-/-, beta2-microglobulin-/- double homozygous mice produced less IL-4 than did either IL-4Ralpha-/- or wild-type mice. These results indicate that an IL-4-independent, beta2-microglobulin-dependent pathway exists through which the CD62L-low CD4+ population has acquired IL-4-producing capacity in vivo, strongly suggesting that these cells are NK T cells.

Leishmania major: a clone with low virulence for BALB/c mice elicits a Th1 type response and protects against infection with a highly virulent clone

BALB/c mice are highly susceptible to infection with Leishmania major and generally develop a severe, nonhealing form of disease following parasite inoculation. As opposed to protective Th1 type immune responses which develop in resistant strains of mice, BALB/c mice develop predominant Th2 type responses characterized by the production of high levels of IL-4, but only low levels of IFN-gamma. However, BALB/c mice will develop resistance and Th1 type responses following the inoculation of very low numbers of L. major promastigotes. In this study, we have examined the effects of parasite virulence on the immune response and disease phenotype in susceptible BALB/c mice. Two clones of L. major were isolated which differed with respect to their in vitro growth rates as promastigotes and their virulence for mice. One rapidly growing clone, L.m.F1, was highly virulent in BALB/c mice and produced nonhealing infections characterized by predominant Th2 type responses. In contrast, a slow-growing clone, L.m.S2, was less virulent in BALB/c mice and produced self-healing infections at parasite doses equivalent to those which produced progressive disease with the more virulent clone. Mice which healed infections with the L.m.S2 clone developed responses characterized by elevated production of IFN-gamma and were resistant to a challenge infection with the virulent L.m.F1 clone. These results suggest that the virulence of individual parasite clones may influence both the course of disease and the phenotype of the immune response which develops during infection.

Successful therapy of chronic, nonhealing murine cutaneous leishmaniasis with sodium stibogluconate and gamma interferon depends on continued interleukin-12 production

Treatment of nonhealing forms of human leishmaniasis with antimonial drugs in combination with gamma interferon (IFN-gamma) may promote healing more effectively than conventional drug therapy. Although the natures of immune responses in patients prior to treatment are often unclear, it is generally assumed that such therapy also promotes a switch from a Th2-type response to a dominant Th1-type response. We have examined the efficacy of IFN-gamma therapy, in combination with drug therapy, to promote healing and a Th2-to-Th1 switch in highly susceptible BALB/c mice infected with Leishmania major. Short-term treatment with the antileishmanial drug sodium stibogluconate failed to significantly alter the course of disease or the immune response when it was given during the third and fourth weeks of infection. IFN-gamma therapy, administered over the same time period, also failed to induce cure or a Th1 dominant response. In contrast, mice treated with a combination of drug and IFN-gamma therapy resolved their infections and developed Th1-type responses. However, administration of an antibody to interleukin 12 (IL-12) reversed the therapeutic effects of therapy with drug plus IFN-gamma, suggesting that IFN-gamma promotes cure through an IL-12-dependent mechanism. Analysis of mRNA levels within parasitized lesions suggests that drug treatment plus IFN-gamma treatment, in addition to reducing parasite numbers, results in reduced levels of IL-4, IL-10, and transforming growth factor beta transcripts but increased levels of transcripts of the p40 chain of IL-12 and inducible nitric oxide synthase, which catalyzes the production of nitric oxide. Together, these results suggest that such immunotherapy may promote the development of a protective Th1-type response in susceptible mice by a mechanism which involves both suppression of regulatory cytokines and enhancement of IL-12 and nitric oxide production.

In differentiated CD4+ T cells, interleukin 4 production is cytokine-autonomous, whereas interferon gamma production is cytokine-dependent

CD4+ T cells from T cell receptor transgenic mice that have been vigorously primed to be interleukin (IL)-4 producers (T(H2) cells) are capable of producing IL-4 even if restimulated in the absence of IL-4 and in the presence of IL-12. T cells vigorously primed in the absence of IL-4 (T(H1) cells) fail to produce IL-4 even if restimulated under conditions that would cause a naive T cell to produce IL-4. In contrast, interferon gamma (IFN-gamma) production is highly cytokine-regulated. T cells primed in the presence of IL-4 develop into IFN-gamma producers if IFN-gamma is included in the priming culture and if the cells are challenged in the presence of IL-12, presumably reflecting the role of IFN-gamma in inducing responsiveness to IL-12. Cells primed in the absence of IL-4 become highly responsive to IL-12 if IFN-gamma is included in the priming culture, and these cells are excellent IFN-gamma producers upon challenge; IL-12 considerably enhances their production of IFN-gamma. If cells are primed in the absence of IL-4 and IFN-gamma, they show very weak responsiveness to IL-12 as determined by STAT-4 activation. However, these cells acquire IL-12 responsiveness if cultured with IFN-gamma for a period as short as 4 hr. Thereafter, they produce large amounts of IFN-gamma upon challenge with antigen in the presence of IL-12. These results indicate that in primed CD4+ T cells, IL-4 production is largely cytokine-autonomous, whereas IFN-gamma production is highly cytokine-regulated.

Interleukin-12 modulates the protective immune response in SCID mice infected with Histoplasma capsulatum

Infection with Histoplasma capsulatum results in a subclinical infection in immunocompetent hosts due to an effective cellular immune response. By contrast, immunodeficient individuals can have a severe disseminated and potentially fatal disease. In a previous study, it was demonstrated that normal mice infected intravenously with H. capsulatum and treated with interleukin-12 (IL-12) at the time of infection were protected from a fatal outcome. In this study, we examined the immunomodulatory effects of IL-12 on disseminated histoplasmosis in immunodeficient SCID mice. SCID mice infected with H. capsulatum and treated with IL-12 showed an increase in survival and a reduction in the colony counts of H. capsulatum in internal organs at 14 days after infection. The protective effect of IL-12 was abrogated if animals were also treated with a neutralizing antibody to gamma interferon (IFN-gamma). IL-12 treatment also resulted in an increase in mRNA expression and protein production for IFN-gamma, tumor necrosis factor alpha (TNF-alpha), and nitric oxide from spleen cells. When IL-12 was combined with amphotericin B (AmB) treatment, there was a significant increase in survival compared with either modality alone. Moreover, combined treatment resulted in an increase in both IFN-gamma and TNF-alpha production, as well as in a substantial reduction in H. capsulatum burden at 35 and 90 days postinfection. This study demonstrates that IL-12 modulates the protective immune response to histoplasmosis in SCID mice and also suggests that IL-12 in combination with AmB may be useful as a treatment for H. capsulatum in immunodeficient hosts.

Generation of atypical pulmonary inflammatory responses in BALB/c mice after immunization with the native attachment (G) glycoprotein of respiratory syncytial virus

The feasibility of using the highly purified native attachment (G) protein in a subunit vaccine against respiratory syncytial virus (RSV) was examined in a murine model with or without the fusion (F) protein of RSV and the adjuvant QS-21. The studies established that QS-21 was more potent than AIOH as an adjuvant for both F and G glycoproteins. Augmented antigen-dependent killer cell activity and complement-assisted serum neutralizing and anti-F and G protein immunoglobulin G2a antibody titers were observed. Immunization with G/QS-21 generated immune responses that were characterized by low levels of antigen-dependent killer cell activity, elevated levels of interleukin-5 (IL-5) and percentages of eosinophils in the bronchoalveolar lavage fluids after challenge, and splenic immunocytes that secreted IL-5 but not gamma interferon (IFN-gamma) after in vitro stimulation with purified whole virus antigens. The pulmonary eosinophilia was similar to that induced by a facsimile of a formalin-inactivated vaccine used in previous clinical trials and was prevented by prior in vivo treatment with anti-IL-5 but not with control immunoglobulin G or anti-IFN-gamma neutralizing monoclonal antibodies. Thus the data implied that vaccination with G/QS-21 generated helper T-cell immune responses that were type 2 in nature. Alternatively, the data suggested that the helper T-cell immune responses elicited by F/QS-21 were more type 1 in character. Neither eosinophilia nor elevated levels of IL-5 were observed in the lungs of mice after challenge. Noteworthy levels of antigen-dependent killer cell activity was observed, and splenic immunocytes secreted copious quantities of IFN-gamma. Immunization with a combination vaccine composed of highly purified native F and G proteins plus QS-21 (F+G/QS-21) resulted in augmented complement-assisted serum neutralizing antibody titers compared with vaccination with either F/QS-21 or G/QS-21 alone. However, following vaccination with F+G/QS-21, the bronchoalveolar lavage fluids contained significant increases in IL-5 and percentages of eosinophils after challenge, the spleen cells appeared to secrete less IFN-gamma after in vitro stimulation, and there was no evidence of increased numbers of antigen-dependent killer cell precursors. Taken together, the data imply that native G protein influences the nature of the immune responses elicited by F/QS-21. The results therefore suggest that G, not F, protein has more potential to bias the host for atypical pulmonary inflammatory responses.

Expression of mammalian cytokines by Trypanosoma cruzi indicates unique signal sequence requirements and processing

A vector based upon the calmodulin-ubiquitin 2.65 locus of Trypanosoma cruzi has enabled the expression and secretion of the murine cytokines interleukin-2 (IL-2) and gamma-interferon (gamma-IFN) by transfected T. cruzi. The T. cruzi-derived cytokines were bioactive and produced by both epimastigotes and mammalian forms. The native coding sequence of IL-2 was sufficient to cause secretion of the protein, but the gamma-IFN signal sequence had to be replaced by the IL-2 signal sequence (IL-2/gamma-IFN) to allow efficient secretion of gamma-IFN. The amino acid sequences at the N-termini of the secreted T. cruzi-derived cytokines were different from the expected murine secreted protein. The secreted IL-2 was cleaved six amino acids downstream from the murine signal sequence cleavage site, and the hybrid IL-2/gamma-IFN molecule was cleaved three amino acids downstream from the predicted signal cleavage site in the IL-2/gamma-IFN molecule. These apparent differences in signal peptide sequence requirements and cleavage sites most likely indicate that the signal sequence processing in trypanosomes is distinct from that of higher eukaryotes.

The influence of the site of parasite inoculation on the development of Th1 and Th2 type immune responses in (BALB/c x C57BL/6) F1 mice infected with Leishmania major

Although inbred strains of mice are classified as genetically resistant or susceptible to Leishmania major based upon their ability to control infection, other factors such as the strain, dose, and site of parasite inoculation can also affect the outcome of the disease. Here we used the F1 progeny of BALB/c (susceptible) and C57BL/6 (resistant) mice (designated CB6F1) to investigate whether mice or intermediate susceptibility to infection differed from the parental strains in their ability to control infections at different cutaneous sites. CB6F1 mice developed progressive disease when inoculated in the dorsal skin, but healed infections in the footpad. Consistent with these observations, mice inoculated in the footpad ultimately developed Th1 responses, known to be required for healing, while Th2 responses developed in mice inoculated in the dorsal skin. However, IL-4 and IFN-gamma production during the first few weeks of infection was similar in CB6F1 mice inoculated at either site, suggesting that factors in addition to the relative levels of these cytokines produced early in infection may influence the nature of the antileishmanial immune response, and the eventual disease outcome. Infection in CB6F1 mice provides a model for the study of immunity to L. major in genetically identical animals, in which a prolonged mixed Th1/Th2 cytokine pattern initially develops, but ultimately diverges into more defined Th1 and Th2 type responses.

Cloning and expression of a Leishmania donovani gene instructed by a peptide isolated from major histocompatibility complex class II molecules of infected macrophages

The studies reported here describe the isolation of peptides from MHC class II molecules of murine macrophages infected with Leishmania donovani, and the use of the derived peptide sequences to rescue the pathogen peptide donor protein. The isolation of the peptides was carried out by comparing the RP HPLC profile of peptides extracted from infected macrophages with the peptides extracted from noninfected cells. Several distinct HPLC peaks unique to infected macrophages were sequenced. One of the peptides that was not homologous to any known protein was used to instruct the designing of an oligonucleotide sense primer that was used in combination with an oligo dT nucleotide (anti-sense primer) to amplify by PCR a DNA fragment from L. donovani cDNA. The amplified DNA fragment was cloned and used as a probe to screen a L. donovani cDNA library. The cloned gene (Ld peptide gene) has an open reading frame of 525 bp and has no homology with any known protein/gene sequence. Northern blot analyses indicated that the Ld peptide/gene is broadly distributed and expressed among species of the Leishmania genus, in both the amastigote and promastigote life cycle forms. Using the pGEX 2T vector, the gene was expressed and the relationship of the purified recombinant protein with L. donovani was confirmed using both antibody and T cell responses from immunized or infected animals. The gene encodes a 23-kD molecule (Ldp 23) associated with the cell surface of L. donovani promastigotes. In addition, T cells purified from the lymph nodes of BALB/c mice immunized with L. donovani or infected with L. major, and from CBA/J mice infected with L. amazonensis were stimulated to proliferate by the recombinant Ldp 23 and produced high levels of IFN-gamma and no IL 4. This observation suggests that the Ldp 23 is an interesting parasite molecule for the studies concerning the host/parasite interaction because the Th1 pattern of cytokine response that it induces is correlated with resistance to Leishmania infections. These results clearly point to an alternative strategy for the purification of proteins useful for the development of both vaccines and immunological diagnostic tools not only against leishmaniasis but also for other diseases caused by intracellular pathogens.

Major histocompatibility complex binding affinity of an antigenic determinant is crucial for the differential secretion of interleukin 4/5 or interferon gamma by T cells

Differential activation of CD4+ T-cell precursors in vivo leads to the development of effectors with unique patterns of lymphokine secretion. To investigate whether the differential pattern of lymphokine secretion is influenced by factors associated with either the display and/or recognition of the ligand, we have used a set of ligands with various class II binding affinities but unchanged T-cell specificity. The ligand that exhibited approximately 10,000-fold higher binding to I-Au considerably increased the frequency of interferon gamma-producing but not interleukin (IL) 4- or IL-5-secreting cells in vivo. Using an established ligand-specific, CD4+ T-cell clone secreting only IL-4, we also demonstrated that stimulation with the highest affinity ligand resulted in interferon gamma production in vitro. In contrast, ligands that demonstrated relatively lower class II binding induced only IL-4 secretion. These data suggest that the major histocompatibility complex binding affinity of antigenic determinants, leading to differential interactions at the T cell-antigen-presenting cell interface, can be crucial for the differential development of cytokine patterns in T cells.

Cellular mechanisms in the immune response to malaria in Plasmodium vinckei-infected mice

Infection of mice with the malaria parasite Plasmodium vinckei vinckei is 100% lethal. However, after two infections followed by drug cure, BALB/c mice develop a solid immunity which is antibody independent but mediated by CD4+ T cells. To elucidate the mechanisms of this immunity, spleen cells from immune mice were challenged in vitro with lysates of P. vinckei-infected or uninfected erythrocytes. The parasite antigen induced proliferation of T cells from immune mice but not from nonimmune mice. When gamma interferon production by cells from immune mice was assayed at the single-cell level, 1 to 3 cells per 1,000 cells were found to release this cytokine when exposed to antigen. In contrast, the numbers of interleukin 4 (IL-4)-producing cells from both immune and control mice were < or = 4 per 10(6) cells, regardless of antigen exposure. Investigation in a bioassay showed that P. vinckei antigen induced the release of IL-4 from spleen cells of immune mice but not from those of control mice. Nevertheless, that IL-4 is of minor significance in this system is also suggested by the absence of elevation of immunoglobulin E levels in blood samples from these mice, in contrast to what is seen with P. chabaudi infection, in which IL-4-producing Th2 cells are of major importance for immunity during later phases of infection. Taken together, the present results indicate that immunity to P. vinckei is a Th1 response, with gamma interferon being an important protective factor. Whether or not the Th1 response, through overproduction of tumor necrosis factor alpha, is also responsible for pathology and death in this infection remains to be clarified.

Antigen presentation by Leishmania mexicana-infected macrophages: activation of helper T cells specific for amastigote cysteine proteinases requires intracellular killing of the parasites

Leishmania mexicana amastigotes proliferate in the phagolysosomes of mammalian macrophages. The parasites abundantly synthesize lysosomal cysteine proteinases, which are encoded by the lmcpb gene family. One of these genes was overexpressed in Escherichia coli, and the purified recombinant protein was used as an antigen to induce and establish a T helper 1 (Th1) cell line. The T cells recognize epitopes shared by the native cysteine proteinases and the recombinant protein. Infected bone marrow-derived macrophages induced to express major histocompatibility complex class II molecules by interferon (IFN)-gamma do not affect parasite viability. These macrophages fail to stimulate the proliferation of the T cell line. In contrast, strong T cell stimulation is observed after the parasites are killed by treatment with L-leucine methylester, or after activation of macrophages by IFN-gamma and tumor necrosis factor-alpha. It is concluded that infected macrophages efficiently present this lysosomal Leishmania antigen once the parasites are inactivated and degraded. This observation may be of considerable relevance for the outcome of Leishmania infections provided that it can be extended to other parasite antigens.

Evidence that cytokine-mediated immune interactions induced by Schistosoma mansoni alter disease outcome in mice concurrently infected with Trichuris muris

In murine models of Schistosoma mansoni infection, egg production is associated with a switch from T helper cell (Th)1- to Th2-type responses to both schistosome-specific and unrelated antigens. Polyparasitism is common in human populations within S. mansoni endemic areas. We have, therefore, examined whether coinfection with S. mansoni could affect the outcome of a second parasitic infection, through Th2 cytokine-dependent modifications to the host immune response. We find that when mice susceptible to infection with the gut nematode Trichuris muris are coinfected with S. mansoni, they acquire the capacity to resolve T. muris infection, thus demonstrating a resistant phenotype. This ability to expel T. muris is associated with the production of Th2-associated cytokines, and corresponding antibody isotypes, in response to S. mansoni egg antigens. The Th2 response shows that there is no compartmentalization between spleen and mesenteric lymph nodes, and that the expulsion of T. muris is not caused by any changes in the host intestine associated with excretion of schistosome eggs. This influence of schistosome infections may be important, not only for the outcome of infections with unrelated pathogens in endemic areas, but also for the efficacy of vaccines in such areas.

Depletion of interleukin-4 in BALB/c mice with established Leishmania major infections increases the efficacy of antimony therapy and promotes Th1-like responses

Whereas most inbred mouse strains mount a protective Th1 helper T-cell response following infection with Leishmania major, an ineffective Th2 response develops in BALB/c mice, leading to the development of disseminated, ultimately fatal disease. Interleukin-4 (IL-4) production is required for the initiation of the Th2 response, though little is known about the requirements for the long-term maintenance of this response. In order to investigate the role of the expanding parasite population on the Th2 response, mice infected for 2 weeks with L. major, which exhibited a Th2-like cytokine profile, were treated with a leishmanicidal agent (Pentostam) and/or various doses of anti-IL-4 antibody. Untreated mice, mice treated with Pentostam alone, or mice treated with 2.5 mg of anti-IL-4 antibody given at days 13 and 21 of infection developed progressive disease. However, in 8 of 10 mice treated with this dose of anti-IL-4 antibody plus Pentostam lesion development was arrested and lesions were either controlled or eventually healed. Healing was associated with the production of high levels of gamma interferon by spleen cells, and low levels of immunoglobulin E in serum compared with levels for control animals, indicating that a Th1-like response had developed in mice receiving both treatments. Thus, depletion of IL-4 only in combination with a reduction in the parasite burden allowed the expression of a Th1 response. When the dose of anti-IL-4 antibody was increased to 5 mg per injection, all mice treated with this dose of antibody, with or without Pentostam therapy, healed. However, combined therapy with Pentostam in mice treated with this dose of antibody had an additional protective effect. As expected, a Th1 response developed in mice treated with this dose of anti-IL-4 antibody with or without combined therapy with Pentostam, whereas a Th2 response developed in control mice. Thus, a significant effect on the course of disease is noted when mice with established L. major infections are treated with anti-IL-4 antibody in combination with Pentostam, suggesting that the combined effect of inhibiting IL-4 and reducing the parasite burden has a dramatic effect on the development of resistance to L. major.

Cross-regulatory role of interferon-gamma (IFN-gamma), IL-4 and IL-10 in schistosome egg granuloma formation: in vivo regulation of Th activity and inflammation

This study examined the relationship of IL-4, IL-10 and IFN-gamma with regard to the local granuloma (GR) and draining lymph node (LN) response to Schistosoma mansoni eggs. Synchronized GR were induced in naive and schistosome-infected mice at the vigorous (8 weeks) and late chronic (20 weeks) stages. In LN cultures, IL-10 and IFN production peaked on day 4 and was greatest for 8 week-infected mice. All GR cultures contained IFN, but compared with naive mice IL-10 production was accelerated at 8 weeks and abrogated at 20 weeks, consistent with expansion and abatement of Th2 activity. Cytokine neutralization was performed in egg-challenged, naive mice that were adoptively sensitized with lymphoid cells from 8 week-infected donors. GR size, GR macrophage tumour necrosis factor (TNF) production and egg antigen-elicited IL-2, IL-4, IL-5, IL-10 and IFN were examined on day 4 of GR formation. Anti-IFN augmented GR area by 40%, increased local IL-4 and IL-10, but decreased IFN and TNF production. In corresponding LN cultures, IFN decreased by about 50%, while IL-2, IL-4, IL-10 and IL-5 increased by nearly two-, four-, five- and six-fold, respectively. Anti-IL-10 did not affect GR size or GR cytokines, but abrogated GR area by 40%, along with a reduction in local IL-4 and TNF production. In LN, IL-4 depletion reduced IL-4 and IL-5 by 60-70% and increased IFN levels. These results support the notion of a cross-regulatory network in which IFN inhibits Th2 and IL-10 inhibits Th1 cells. IL-4 fosters Th2 cells differentiation in LN, but also performs a critical recruitment function in the eosinophil-rich schistosome egg-induced GR, whereas IFN contributes to enhanced GR macrophage function.

Increased susceptibility of mice infected with Schistosoma mansoni to recombinant vaccinia virus: association of viral persistence with egg granuloma formation

BALB/c mice infected 7 weeks previously with Schistosoma mansoni and challenged with a recombinant vaccinia virus vPE16 expressing the human immunodeficiency virus envelope protein gp160 show a marked delay in hepatic viral clearance as compared to mice infected with vPE16 alone. This increase in viral persistence is accompanied by reduced gp120-specific Th1-associated cytokine responses as well as by impaired cytotoxic T lymphocyte (CTL) activity against targets expressing epitopes of the same antigen. To investigate the contribution of these defects to the observed delay in clearance of recombinant vaccinia virus, animals were challenged with vPE16 at different times following S. mansoni infection, and virus titers in tissues and viral-specific immune responses were measured simultaneously in the same animals. While normal resolution of virus occurred in schistosome-infected mice prior to parasite egg deposition, persistence within the liver was observed in animals challenged during the onset and peak phase of granuloma formation (6 to 8 weeks after S. mansoni infection). At later times, when schistosomiasis is in its chronic phase, normal viral clearance returned. This time course of viral resolution correlated in part with the observed pattern of decreased Th1 cytokine production toward viral antigens but was clearly less temporally related to the defect in virus-specific CTL activity. Immunohistochemical staining of liver sections from vaccinia/S. mansoni co-infected mice with polyclonal anti-vaccinia antibodies revealed that viral epitopes are localized primarily within granulomas. These experiments suggest that egg granulomas, by providing a microenvironment for viral expression, in combination with the cytokine imbalance present during schistosome infection, can promote the expansion of vaccinia virus and possibly other viral agents.

CD8+ T lymphocytes are the major cell population involved in the early gamma interferon response and resistance to acute primary Toxoplasma gondii infection in mice

Gamma interferon (IFN-gamma) is known to be a major mediator influencing host defense against Toxoplasma (T.) gondii. To evaluate lymphocyte populations involved in this cytokine-mediated early resistance to T. gondii, the effects of in vivo administration of monoclonal antibodies (MAbs) against T-cell subsets and anti-asialo GM1 antibody on the course of infection and IFN-gamma response were investigated in mice infected acutely with this parasitic protozoan. A single injection of anti-CD8 MAb on day -1 or day 4 severely exacerbated the infection, in accordance with a marked suppression of endogenous IFN-gamma production. Moreover, the administration of anti-IFN-gamma MAb on day 0 but not later than day 4 resulted in a total abrogation of resistance to T. gondii, suggesting that endogenous IFN-gamma produced during the first several days of infection is critical for the generation of antitoxoplasmal resistance in mice. In contrast, no significant increase in mortality was observed when injected with either anti-CD4 MAb or anti-asialo GM1 antibody on day -1, while these antibodies reduced significantly the ability of mice to produce IFN-gamma. Indeed, simultaneous depletion of CD4+ and CD8+ cells had no greater suppressive effect on host defense and endogenous IFN-gamma production than depletion of CD8+ cells alone. Together, these results suggest that CD8+ T cells play a central role for resolution of acute toxoplasmosis by participating in endogenous IFN-gamma production. The possible role of early produced IFN-gamma in the development of protective immune response to T. gondii is also discussed.

Site-specific immunity to Leishmania major in SWR mice: the site of infection influences susceptibility and expression of the antileishmanial immune response

Inbred strains of mice usually develop either of two divergent patterns of infection in response to Leishmania major. Resistant mice, which develop self-limiting infections, respond immunologically with the activation of gamma interferon-secreting Th1 helper T cells, while nonhealing infections in susceptible mice are characterized by the proliferation of interleukin-4-secreting Th2 cells. Development of these divergent responses is dependent primarily on the strain of mouse infected, although factors such as the infective dose, species, and strain of parasite can also influence the degree of resistance. In this study, we show that a single mouse strain, SWR, can develop totally divergent patterns of infection depending on the site of parasite inoculation. Both SWR mice and highly susceptible BALB/c mice developed progressive, ultimately fatal disease when inoculated in the dorsal skin over the base of the tail. However, SWR mice infected in the hind footpad developed far less severe infections, which were for the most part controlled, whereas BALB/c mice infected in this site developed severe, nonhealing lesions. Production of gamma interferon and interleukin-4 and measurement of immunoglobulin E levels in serum were used to assess the degree of Th1 and Th2 cell activation in infected mice. Cytokine profiles early in infection had characteristics of a mixed Th1-Th2 response and were similar in SWR mice infected at either site. These early cytokine responses were not predictive of the ultimate disease outcome, since lymph node cells from healing mice eventually produced higher levels of gamma interferon than did those from nonhealing mice, and healing mice had lower levels of immunoglobulin E in serum, suggesting a functional bias toward Th1 cell activity in these animals. The differential ability of SWR mice to heal infections at different cutaneous sites provides a new model for the study of resistance to cutaneous leishmaniasis. Unlike traditional models of infection in which resistant and susceptible strains of mice are compared, this model allows for the study of factors that contribute to healing and nonhealing infections in a genetically identical strain of mouse.

Complete protection against Plasmodium yoelii by adoptive transfer of a CD8+ cytotoxic T-cell clone recognizing sporozoite surface protein 2

BALB/c mice immunized with irradiated Plasmodium yoelii sporozoites produce antibodies and cytotoxic T lymphocytes against the circumsporozoite protein and against a 140-kDa protein, sporozoite surface protein 2 (PySSP2). Approximately 50% of mice immunized with P815 cells transfected with the gene encoding PySSP2 are protected against malaria, and this protection is reversed by in vivo depletion of CD8+ T cells. To determine if CD8+ T cells against PySSP2 are adequate to protect against malaria in the absence of other malaria-specific immune responses, we produced three CD8+ T-cell clones by stimulating spleen cells from mice immunized with irradiated P. yoelii sporozoites with a mitomycin-treated P815 cell clone transfected with the PySSP2 gene. Adoptive transfer of clone TSLB7 protected 100% of mice against P. yoelii. The second clone protected 58% of mice, and the third clone provided no protection. Clone TSLB7 protected even when administered 3 h after sporozoite inoculation at a time when sporozoites had entered hepatocytes, suggesting that it is recognizing and eliminating infected hepatocytes. These studies demonstrate that cytotoxic T lymphocytes against PySSP2 can protect against P. yoelii sporozoite challenge in the absence of other parasite-specific immune responses.

Cell-mediated responses of immunized vervet monkeys to defined Leishmania T-cell epitopes

A population of vervet monkeys was immunized with killed parasites and infected with Leishmania major promastigotes either by needle or by infected-fly bite. The responses of recovered monkeys to mitogens, killed parasites, and molecularly defined T-cell epitopes were then compared with those of control animals. Peripheral blood mononuclear cells (PBMC) from both naive and recovered animals proliferated strongly in response to both B- and T-cell mitogens, although the responses of the recovered animals were less strong than those of the naive animals. Cells from recovered vervets, but not those from naive vervets, also proliferated in response to parasite antigens and synthetic T-cell epitopes. Likewise, cells from recovered animals released gamma interferon and either interleukin 2 (IL-2) or IL-4 into culture media in response to both of the above-mentioned antigens, whereas cells from control animals did not. The fact that no IL-5 could be measured following parasite antigen or synthetic T-cell epitope stimulation of PBMC suggested that cells proliferating in response to these molecules belonged to the Th1 subset. Phenotypic analysis of the PBMC showed a marked increase in T-cell but not B-cell populations in recovered animals. Among this population was an increased number of CD45R0+ memory cells. The data from this study are in keeping with the earlier finding that vervet monkeys provide an excellent model system for leishmaniasis. Further, these data support the contention that synthetic T-cell epitopes are prime candidates for molecularly defined Leishmania vaccines.

CD4pos, NK1.1pos T cells promptly produce interleukin 4 in response to in vivo challenge with anti-CD3

Injection of anti-CD3 antibodies causes prompt expression of interleukin (IL)-4, IL-2, and interferon gamma (IFN-gamma) mRNA among spleen cells. The optimal dose of anti-CD3 for such induction was 1.33 microgram/animal; lymphokine mRNA was first observed at 30 min, peaked at 90 min, and was undetectable (for IL-4) or had declined markedly by 4 h. Cells harvested from spleens of mice injected with anti-CD3 90 min earlier secreted IL-4, IL-2, and IFN-gamma without further stimulation. By contrast, in vitro stimulation with anti-CD3 of spleen cell suspensions or splenic fragments from noninjected donors failed to cause prompt production of IL-4 and, even after 24 h of stimulation, the amount of IL-4 produced in such cells was substantially less than that secreted within 1 h by spleen cell suspensions or splenic fragments from mice injected with anti-CD3 90 min earlier. Production of IL-4 by spleen cells from anti-CD3-injected mice was not inhibited by pretreatment with anti-IL-4 antibody or with IFN-gamma or tumor growth factor beta nor enhanced by treatment with IL-4. By contrast, CTLA-4 immunoglobulin (Ig) treatment clearly diminished IL-4 production in response to in vivo anti-CD3, indicating that cellular interactions involving CD28 (or related molecules) were important in stimulation. Cell sorting analysis indicated that the cells that produced IL-4 in response to in vivo injection of anti-CD3 were highly enriched in CD4pos cells with the phenotype leukocyte cell adhesion molecule-1 (LECAM-1)dull, CD44bright, CD45RBdull, NK1.1pos. Indeed, the small population of CD4pos, NK1.1pos cells had the great majority of the IL-4-producing activity of this population. Injection with Staphylococcal enterotoxin B also caused prompt induction of IL-4 mRNA; the cells that were principally responsible for production also had the phenotype of CD4pos, NK1.1pos. These results suggest that possibility that this rare population of T cells may be capable of secreting IL-4 at the outset of immune responses and thus may act to regulate the pattern of priming of naive T cells, by providing a source of IL-4 to favor the development of T cell helper 2-like IL-4-producing cells.

Schistosoma mansoni egg-primed Th0 and Th2 cells: failure to down-regulate IFN-gamma production following in vitro culture

Schistosoma mansoni eggs induce a rapid and pronounced Th response which, based on cytokine secretion patterns, at day 3 post priming is Th0-like and at day 10 is Th2-like. To establish whether or not the day-3 cells have been programmed in vivo to develop into Th2 cells, they were cultured for 7 days to become in vitro equivalents of day-10 in vivo cells. Following this culture period, the population was approximately 75% CD4+, 22% CD8%, 6% B220+ and capable of producing IL-2, IFN-gamma, IL-4, -5 and -10 upon stimulation. This Th0-like status was confirmed by the observations that in response to mitogen IL-4 and IFN-gamma production are both CD(4+)-cell dependent and that IFN-gamma and IL-4 are produced concomitantly by single cells. These data suggest that Th0 cells persist in vivo, but are incapable of secreting IFN-gamma at day 10 due to an inhibitory factor which does not develop or is labile in vitro. This concept is supported by the surprising observation that day-10 LN cells, which are Th2-like immediately ex-vivo, rapidly gain the ability to secrete IFN-gamma following a short period of culture.

CD28-mediated costimulation of interleukin 2 (IL-2) production plays a critical role in T cell priming for IL-4 and interferon gamma production

Naive T cells require interleukin 4 (IL-4) to develop into IL-4-producing T cells and IL-4 blocks development of such cells into interferon gamma (IFN-gamma) producers. Prior studies in accessory cell-independent priming systems using antireceptor antibodies as agonists have demonstrated that IL-2 is also necessary for the development of IL-4-producing cells under these culture conditions. Here we have examined the role of IL-2 and the CD28 costimulation pathway in priming for IL-4 and IFN-gamma production using a more physiologic model. This involved antigen presentation by accessory cells to naive CD4+ T cells from transgenic mice whose cells express a T cell receptor (TCR) specific for a cytochrome c peptide in association with I-Ek. With splenic antigen-presenting cells (APCs), inhibition of CD28 costimulation by the fusion protein CTLA4-immunoglobulin (Ig) blocked effective priming. Similarly, transfected fibroblasts expressing both MHC class II and the CD28 ligand B7 could prime for IL-4 production and such priming also was blocked by CTLA4-Ig. However, APCs deficient in CD28 ligands also could prime TCR transgenic T cells to become IL-4 producers if an exogenous source of IL-2, as well as IL-4, was provided, and the inhibition of priming seen with splenic or transfected fibroblast APCs in the presence of CTLA4-Ig could be reversed by addition of IL-2. Likewise, priming for IFN-gamma production could be blocked by CTLA4-Ig and reversed by IL-2. Thus, we conclude that IL-2 plays a critical role in priming naive CD4+ T cells to become IL-4 or IFN-gamma producers. Engagement of the CD28 pathway, although normally important in such priming, is unnecessary in the presence of exogenous IL-2.

Interleukin 12 acts directly on CD4+ T cells to enhance priming for interferon gamma production and diminishes interleukin 4 inhibition of such priming

Naive CD4+ T cells produce interleukin 2 (IL-2) but little IL-4 or interferon gamma (IFN-gamma). In vitro, they develop into IL-4 or IFN-gamma producers depending on the conditions of the priming culture. Using T-cell receptor transgenic CD4+ T cells, the role of IL-12 and IL-4 in antigen-specific priming was examined. IL-12 substantially enhanced the ability of naive CD4+ T cells to develop into cells that produced IFN-gamma upon restimulation. However, it was not essential since anti-IL-12 antibodies failed to block the priming for IFN-gamma observed in the absence of exogenous IL-12. When both IL-12 and IL-4 were present in the priming culture, IL-12 did not inhibit priming for IL-4 production. In contrast, IL-4 diminished but did not abolish priming for IFN-gamma production. In an accessory cell-independent priming system, IL-12 strikingly augmented priming for IFN-gamma production, indicating that it acts directly on T cells. IFN-gamma itself did not enhance priming for IFN-gamma production in either accessory cell-dependent or independent systems. In an accessory cell-dependent system, the IL-12-mediated enhancement was not blocked by adding neutralizing anti-IFN-gamma monoclonal antibody. However, in an accessory cell-independent system, anti-IFN-gamma antibody did inhibit priming for IFN-gamma production leaving open a role for IFN-gamma in the priming process. These data indicate that IL-12 has a major effect on the inductive phase of T-cell priming by enhancing commitment to IFN-gamma production and thus can profoundly influence the state of immunity that develops.

A simple, sensitive, dual mAb based ELISA for murine gamma interferon determination: comparison with two common bioassays

Three assays of murine IFN gamma are compared in terms of sensitivity, intra- and inter-assay variability, specificity and simplicity. The widely used viral inhibition assay requires 48 hours, necessitates continuous maintenance and optimization of fibroblast growth, and exhibits the lowest sensitivity. Inhibition of WEHI-279 B cell [3H]thymidine incorporation requires 48-60 hours to quantitate IFN gamma production, can be subject to non-specific inhibition, and is also labor intensive. In both bioassays, specificity must be determined by the analysis of duplicate samples in the presence of neutralizing, IFN gamma-specific mAb. In contrast, a 24 hour, dual mAb ELISA, in which IFN gamma is captured by immobilized, purified rat IgG1 XMG 1.2 mAb and identified with biotinylated mAb R4-6A2 and streptavidin-alkaline phosphatase detects IFN gamma production > 0.05 U/ml. The quantitative range in this assay is typically from 1-100 U/ml. In addition to providing the greatest specificity and shortest duration, this ELISA exhibits the lowest coefficient of variation of the three assays compared. Collectively, assay characteristics such as sensitivity, absence of interference by other proteins, reproducibility, speed and simplicity support the conclusion that this dual mAb based sandwich ELISA represents a substantial improvement over inhibition of viral cytopathic effect or inhibition of WEHI-279 bioassays for characterization of antigen- or mitogen-driven IFN gamma production.

Gamma interferon functions in resistance to Cryptosporidium parvum infection in severe combined immunodeficient mice

Severe combined immunodeficient (SCID) adult mice are relatively resistant to Cryptosporidium parvum infection, even though they are deficient in both T- and B-cell function. The requirement for gamma interferon (IFN-gamma) in this resistance was examined by treatment of these mice with monoclonal antibody to IFN-gamma. SCID mice injected intraperitoneally with monoclonal anti-IFN-gamma 4 h before and three times weekly after challenge with C. parvum had heavy intestinal infections 3 weeks postchallenge. SCID mice similarly injected with irrelevant antibody were not infected. Furthermore, SCID mice receiving a single injection of anti-IFN-gamma either 2 h before or 18 h after challenge were also susceptible to infection. Although IFN-gamma was not detected in SCID mouse intestinal samples, it was found in the supernatant of SCID mouse splenocyte cultures after stimulation with C. parvum antigens. On the other hand, SCID mice receiving multiple injections of antibodies against tumor necrosis factor remained resistant to infection. These data indicate that the resistance of SCID mice to C. parvum infection is IFN-gamma dependent, whereas tumor necrosis factor appears not to play a significant role.

Natural killer cells are a source of interferon gamma that drives differentiation of CD4+ T cell subsets and induces early resistance to Leishmania major in mice

Infection of mice with the protozoan Leishmania major provides an excellent model to define the factors involved in T helper (Th) subset development, since Th1 cells confer protection in resistant strains of mice, whereas Th2 cells are associated with the fatal outcome of susceptible mice. We previously found that interferon gamma (IFN-gamma) was required for Th1 cell development after infection of mice with L. major. In this report, we evaluate the contribution of natural killer (NK) cells to IFN-gamma levels early in L. major infection. NK cell activity was higher in resistant C3H/HeN mice than in susceptible BALB/c mice during the first week of infection, and removal of NK cells significantly decreased IFN-gamma levels and promoted interleukin 4 (IL-4) production in both the draining lymph nodes and spleen. IFN-gamma production by NK cells required the presence of CD4+ T cells or IL-2, but not CD8+ T cells. Enhanced disease, as measured by parasite numbers and lesion development, was observed in NK cell-depleted mice. Furthermore, a comparison of the NK cell response and the subsequent parasite burden in several inbred strains of mice demonstrated that NK cells mediate early resistance to L. major. Together, these data indicate that the stimulation of NK cells, through the production of IFN-gamma, plays an important role in initiating Th1 cell differentiation in leishmaniasis and in controlling early resistance to L. major.

Interleukin 4 suppresses interleukin 2 and interferon gamma production by naive T cells stimulated by accessory cell-dependent receptor engagement

Interleukin 2 (IL-2) and interferon gamma (IFN-gamma) production by CD4+ T cells and IFN-gamma production by CD8+ T cells from naive mice in response to soluble anti-CD3 and antigen-presenting cells (APCs) were strikingly inhibited by culture in the presence of IL-4. IL-4 decreased IL-2 and IFN-gamma mRNA levels after 15-24 hr but gave relatively little decrease in these mRNAs at 6-12 hr after stimulation with soluble anti-CD3. A 16-hr preculture of T cells with anti-CD3, APCs, and IL-4 was sufficient to inhibit subsequent production of IL-2 and IFN-gamma in response to restimulation in the absence of IL-4. Furthermore, IL-4 treatment of T cells purified 24 hr after stimulation inhibited their capacity to subsequently produce IL-2 in response to anti-CD3 and APCs, indicating that T cells were targets of IL-4-mediated inhibition. IL-4 blocked acute IL-2 production in response to a cytochrome c peptide of T cells derived from transgenic mice expressing T-cell receptors specific for cytochrome c but it did not block IL-2 production by such cells after they had been primed in vitro. Nor did IL-4 inhibit production of IFN-gamma by cloned T cells in response to antigen and APCs or production of IL-2 and IFN-gamma by naive T cells in response to phorbol ester and calcium ionophore. These results indicate that IL-4 strikingly inhibits IL-2 and IFN-gamma production by naive T cells in response to accessory cell-dependent, receptor-mediated stimulation (i.e., soluble anti-CD3 and APCs or antigen and APCs) but does not inhibit accessory cell-independent stimulation of naive T cells or accessory cell-dependent receptor-mediated stimulation of recently primed T cells or cloned T-cell lines.

Cross-protection against lymphocytic choriomeningitis virus mediated by a CD4+ T-cell clone specific for an envelope glycoprotein epitope of Lassa virus

Recombinant vaccinia virus expressing the Lassa virus (LV) envelope glycoprotein precursor, V-LSGPC, was used to study the basis of LV-induced cross-protective immunity against the closely related arenavirus lymphocytic choriomeningitis virus (LCMV). C3H/HeJ mice primed with V-LSGPC developed neither circulating antibodies nor CD8+ cytotoxic T cells specific for LCMV, yet they resisted a normally lethal LCMV challenge. Spleen cells from such mice gave a proliferative response to LCMV in vitro that was inhibitable by anti-CD4 antibody. Synthetic peptides corresponding to predicted T-cell sites common to the envelope glycoprotein precursor (GP-C) of LV and that of LCMV were used to map the specificity of the proliferative response to an epitope located between amino acids 403 and 417 of LV GP-C. Several CD4+ T-cell clones specific for the 403-417 peptide were isolated and found to produce gamma interferon in response to both the peptide and LCMV. One of these clones, C9, was selected for further study. C9 lysed I-AK-bearing target cells, and when adoptively transferred to C3H/HeJ mice, it was capable of mediating both a peptide-specific delayed hypersensitivity reaction and resistance to lethal LCMV challenge. These collective findings demonstrate, for the first time, that CD4+ T cells can play a major role in arenavirus-specific cross-protective immunity.