Interaction and activation of antigen-specific T and B cells

Scurfin (FoxP3) controls T-dependent immune responses in vivo through regulation of CD4+ T cell effector function

Scurfin, the protein product of the FoxP3 gene, is a forkhead-family transcription factor that negatively regulates T cell function. Mice carrying a loss-of-function mutation in FoxP3 (scurfy mice) present with fatal autoimmune-like disease caused by hyperresponsive CD4(+) T cells. Mice that overexpress scurfin (FoxP3 Tg mice) possess fewer mature T cells with reduced functional capabilities compared with normal littermate control mice. We analyzed the ability of CD4(+) T cells and B cells from FoxP3 Tg mice to respond to a T-dependent Ag and found that immunized FoxP3 Tg mice displayed reduced total and Ag-specific serum Ig and disorganized splenic architecture. However, when cultured in vitro, FoxP3 Tg B cells responded normally, suggesting that the poor Ab response was a result of defective T cell help in vivo. When challenged, CD4(+) T cells from FoxP3 Tg mice display reduced up-regulation of CD40 ligand and fewer IFN-gamma-producing cells. Overall, these findings show that overexpression of scurfin reduces T cell responses in vivo such that CD4(+) T cells cannot provide help to B cells during a T cell-dependent Ab response.

Cryptic determinants and promiscuous sequences on human acetylcholine receptor: HLA-dependent dichotomy in T-cell function

Experimental autoimmune myasthenia gravis can be induced in some strains of mice and rats by immunizing with acetylcholine receptor. Also, epidemiologic studies demonstrate an MHC linkage of myasthenia gravis in the man. In order to obtain direct experimental evidence for the influence of the genes of the MHC complex in the development of myasthenia gravis, we used mice transgenic to individual HLA molecules. We observed an increased susceptibility to the disease in HLA DQ8 transgenic mice compared to HLA DQ6 transgenic mice ( J. Immunol. 160:4169; 1998). These mice lacked endogenous mouse class II molecules. In the present study we mapped the cryptic and dominant sequences on the extra cellular region of human acetylcholine receptor. Although some epitopes (e.g., alpha11-30, alpha141-160, alpha171-190) were common between DQ8 and DQ6 transgenic mice, several others were disparately recognized. We also found a functional dichotomy in T cells from mice differing by one MHC molecule (HLA DQ8 or DQ6) when primed by sequences immunodominant in DQ8 and DQ6 tg mice. Differential disease manifestation in the two different HLA transgenic mice could be explained not only by differential recognition of peptides by these antigen presenting molecules, but also by the difference in the functional profile of T cells generated when primed by promiscuous sequence regions.

Activation of antigen-specific CD4+ Th2 cells and B cells in vivo increases norepinephrine release in the spleen and bone marrow

The neurotransmitter norepinephrine (NE) binds to the beta 2-adrenergic receptor (beta 2AR) expressed on various immune cells to influence cell homing, proliferation, and function. Previous reports showed that NE stimulation of the B cell beta 2AR is necessary for the maintenance of an optimal primary and secondary Th2 cell-dependent Ab response in vivo. In the present study we investigated the mechanism by which activation of Ag-specific CD4+ Th2 cells and B cells in vivo by a soluble protein Ag increases NE release in the spleen and bone marrow. Our model system used scid mice that were reconstituted with a clone of keyhole limpet hemocyanin-specific Th2 cells and trinitrophenyl-specific B cells. Following immunization, the rate of NE release in the spleen and bone marrow was determined using [3H]NE turnover analysis. Immunization of reconstituted scid mice with a cognate Ag increased the rate of NE release in the spleen and bone marrow 18-25 h, but not 1-8 h, following immunization. In contrast, immunization of mice with a noncognate Ag had no effect on the rate of NE release at any time. The cognate Ag-induced increase in NE release was partially blocked by ganglionic blockade with chlorisondamine, suggesting a role for both pre- and postganglionic signals in regulating NE release. Thus, activation of Ag-specific Th2 cells and B cells in vivo by a soluble protein Ag increases the rate of NE release and turnover in the spleen and bone marrow 18-25 h after immunization.

Stimulation of the B cell receptor, CD86 (B7-2), and the beta 2-adrenergic receptor intrinsically modulates the level of IgG1 and IgE produced per B cell

Our findings using B cells from either wild-type, CD86-deficient, or beta 2-adrenergic receptor (beta2AR)-deficient mice suggest three mechanisms by which the level of IgG1 and IgE production can be increased on a per cell basis. Trinitrophenyl-specific B cells enriched from unimmunized mouse spleens were pre-exposed to Ag and/or the beta 2AR ligand terbutaline for 24 h before being activated by either a beta 2AR-negative Th2 cell clone or CD40 ligand/Sf9 cells and IL-4 in the presence or absence of an anti-CD86 Ab. Data suggest that the first mechanism involves a B cell receptor (BCR)-dependent up-regulation of CD86 expression that, when CD86 is stimulated, increases the amount of IgG1 and IgE produced in comparison to unstimulated cells. The second mechanism involves a BCR- and beta 2AR-dependent up-regulation of CD86 to a level higher than that induced by stimulation of either receptor alone that, when CD86 is stimulated, further increases the amount of IgG1 and IgE produced. The third mechanism is BCR-independent and involves a beta 2AR-dependent increase in the ability of a B cell to respond to IL-4. Flow cytometric and limiting dilution analyses suggest that the increase in IgG1 and IgE occurs independently from the isotype switching event. These findings suggest that the BCR, the beta 2AR, and CD86 are involved in regulating IL-4-dependent IgG1 and IgE production.

Suppression of Antigen-Specific Th2 Cell-Dependent IgM and IgG1 Production Following Norepinephrine Depletion In Vivo

The mechanism by which the Th2 cell-dependent Ab response is modulated by the sympathetic neurotransmitter norepinephrine (NE) was investigated. Our model system used the severe combined immunodeficient (scid) mouse that was depleted of NE with 6-hydroxydopamine before reconstitution with a clone of β2-adrenergic receptor (β2AR)neg KLH-specific Th2 cells and resting trinitrophenyl (TNP)-specific β2ARpos B cells enriched from the spleens of unimmunized mice. Following challenge with TNP-keyhole limpet hemocyanin (KLH), Ab production in these mice was hapten-, carrier-, and allotype-specific as well as MHC restricted. Depletion of NE resulted in a 50–75% suppression of the primary anti-TNP IgM response compared with that of NE-intact controls, while the secondary IgM response returned to control levels. In contrast, both the primary and secondary anti-TNP IgG1 responses were suppressed by 85 and 40%, respectively. Using NE-intact mice exposed to either a βAR- or αAR-selective antagonist, the effect of NE on the Ab response was shown to be mediated by the βAR. In addition, administration of a β2AR-selective agonist to NE-depleted mice partially reversed the suppressed Ab response that resulted from NE depletion. Expression of the β2AR on TNP-specific B cells was confirmed by radioligand binding, immunofluorescence, and cAMP analysis. Also, while splenic histology was comparable in NE-intact and NE-depleted mice before Ag exposure, follicle expansion and germinal center formation were suppressed in NE-depleted mice after Ag exposure. Taken together, these results suggest that NE stimulation of the β2AR expressed on B cells is necessary for the maintenance of an optimal primary and secondary Th2 cell-dependent Ab response in vivo.

Engagement of the B-cell antigen receptor by antigen negatively regulates IgE production by antigen-specific B cells

BACKGROUND

Functional differentiation of B lymphocytes can be regulated at different levels. Such B-cell responses, to a large extent, are under the control of T cells and the release of soluble factors from these cells. Crosslinking of B-cell antigen receptors also can direct B-cell differentiation, although the mechanisms are not well defined and the effects on specific antibody production have not been examined.

OBJECTIVE

This study was conducted to determine whether crosslinking of the B-cell antigen receptor by antigen or antibody to the B-cell receptor could modulate specific antibody production, especially IgE production.

METHODS

Antigen-specific human B cells were isolated and incubated with antigen or antibody to the B-cell antigen receptor. Specific antibody production was examined, as were surface isotype expression and levels of Ig heavy chain mRNA in T cell-independent cultures.

RESULTS

The addition of antigen or anti-IgM antibody enhanced IgM and IgG antibody production in the presence of anti-CD40 and IL-4 but downregulated IgE synthesis. These changes in isotope production paralleled changes in the frequencies of surface Ig+ B cells and Ig mRNA levels. Exogenous IL-6 abolished the antigen-mediated downregulation of IgE production.

CONCLUSIONS

These studies indicate that signals delivered by means of the B-cell antigen receptor regulate antibody production in a distinct manner, resulting in enhanced IgM and IgG responses but leading to the inhibition of IgE production. Endogenous IL-6 production by B cells may counter the negative regulatory effects of antigen on IgE synthesis. We suggest that although antigen-mediated T/B-cell interactions play a major role in IgM- and IgG-specific antibody production, antigen-independent interactions may be more effective for T-cell dependent, IL-4-induced IgE production by antigen-specific B cells. Furthermore, these findings provide a basis for further understanding of allergic responses and modulation by immunotherapy, where repeated exposure to large concentrations of allergen, administered by means of injection, enhance IgG responses and downregulate IgE synthesis.

Ultralow concentrations of proenkephalin and [met5]-enkephalin differentially affect IgM and IgG production by B cells

Resting mouse splenic B cells were activated with lipopolysaccharide/dextran sulfate (LPS/DxS) to measure both B cell proliferation and IgM/IgG isotype production when increasing concentrations of [Met5]-enkephalin (MENK) and proenkephalin (PENK) (10-16 to 10(-8) M) were added at increasing times after B cell activation (0, 3, 6, or 24 h). Results show that proliferation was not affected by either peptide, but that IgM, IgG3 and IgG2a production were inhibited in a concentration- and time-dependent manner by MENK. IgG1 production was unaffected by MENK. In contrast, PENK induced no change in the production of Ig isotypes at any time point of addition, with the exception of IgG1 and IgG2a that were enhanced when PENK was added 6 h after cell activation. In the absence of LPS/DxS activation, no change in the level of any Ig isotype was induced by either peptide.

The effect of IL-4 on antigen expression: a comparison of fluorescence intensity and antigen density

We have compared the membrane expression of MHC class II antigen and Ig on murine splenic B lymphocytes by two flow cytometric methods. The first method, commonly used, determined the mean immunofluorescence intensity; the second measured antigen density as a ratio of mean fluorescence intensity to cell volume. The data generated by the two methods allow for different interpretations of antigen density in comparison to antigen expression. By mean fluorescence intensity, activated B lymphocytes expressed more MHC class II antigen and membrane Ig than did resting B cells. However, resting B cells had the same density of MHC class II antigen and membrane Ig as activated B cells. Next we examined the effect of IL-4 on antigen expression by the two methods. We found that although IL-4 increased the mean fluorescence intensity and density of MHC class II and membrane Ig on each B cell population, the density of expression of membrane Ig tended to be greater on the resting B cells than on the activated, while the density of MHC class II antigen was essentially the same on each of the IL-4 treated B cell populations.

Lipophilic multiple antigen peptide system for peptide immunogen and synthetic vaccine

We describe the development and structural requirements of a new lipophilic multiple antigen peptide (lipoMAP) system for immunogens that contains a built-in lipophilic adjuvant and has the ability to elicit cytotoxic T-lymphocytes (CTLs). In addition to the peptide antigens of choice at the amino terminus, the basic lipoMAP design consists of three components: a tetravalent symmetrical core matrix containing two levels of branching beta-alanyl-lysine as a building unit, a hydrophilic Ser-Ser dipeptide linker, and at the carboxyl terminus, palmitoyl lysines (PL) with alternating chirality. An 18-residue peptide from the third variable region in the gp120 of HIV-1 was used as antigen in eight models for a structure-function study. Alternating palmitoyl lysine (PL) was introduced as the lipid anchor and built-in adjuvant because D and L Lys (Pal) was found via molecular modeling to best mimic phosphatidylcholine and thus provide the most stable peptide antigens on the ordered lipid membranes. The requirements of the palmitoyl lysines and the L-Ser-L-Ser linker were crucial, since replacement with palmitoyl serines or L-Ser-D-Ser linkers led to a marked decrease in immune response. The stoichimetric ratio of PL vs MAP was also important. Multiple antigen peptide (MAP) constructs without the lipophilic PLs, those that were underlipidated and contained one PL, or those that were overlipidated containing four PLs, were ineffective. LipoMAPs containing three palmitic acids elicited significant humoral responses in oil-based emulsion and liposomes, but not in water or alum formulations. LipoMAP containing only two PLs was found best to be incorporated in liposomes and elicited a significant immune response and cytotoxic T-lymphocytes (CTLs). These models were compared favorably with a preparation using tripalmitoyl-S-glyceryl cysteine (P3C) as the lipid anchor. We also developed a modular synthesis of MAP-P3C that incorporated P3C as a premade unit containing a thiopyridine, which simplified the overall scheme and minimized oxidation during stepwise peptide synthesis. This lipoMAP model is a new addition to the design of our macromolecular assemblage approach mimicking peptide antigens on the surface of micro-organisms. It may be a potentially useful approach to the design of a synthetic vaccine for humans.

Enhanced immunogenicity of protein-dextran conjugates: I. Rapid stimulation of enhanced antibody responses to poorly immunogenic molecules

In view of our observation that anti-immunoglobulin antibody conjugated to high-molecular-weight dextran stimulates high levels of B-cell activation (Brunswick et al. J. Immunol. 1989, 143, 1239), we coupled T cell-dependent antigens to dextran. When mice were immunized, in the absence of adjuvant, with a BSA-dextran conjugate (BSA-dex), a persistent, high-titre anti-BSA IgG1 response was induced. Titres were dose-dependent and seen with as little as 10 micrograms of conjugated protein. Anti-BSA titres were detected as early as day 7, usually peaked at about day 14 and persisted for at least 4 weeks. Anti-hapten antibodies were also elicited in mice that were immunized with haptenated BSA covalently bound to dextran, and secondary responses could be induced even after inoculation of the unconjugated protein. Covalent attachment of the protein to the polymer was necessary, and the response was specific, as coinjection of BSA-dex and an unrelated antigen, goat IgG, did not elicit detectable anti-goat antibodies. The immunogenic potential of these conjugates did not depend on the ability of the dextran carrier to induce antibody, inasmuch as they stimulated high levels of anti-protein antibody in mice unresponsive to dextran. A minimum size dextran polymer was required for enhanced immunogenicity as conjugates of BSA with dextran of molecular mass 500 or 2000 kDa but not of 70 kDa gave detectable anti-BSA titres.

Giant cell formation in Hodgkin's disease

The identity of Reed-Sternberg cells in Hodgkin's disease has remained an unresolved issue, though many studies have addressed this question. Giant cells are usually formed either by endomitosis without cytoplasmic division or by cell fusion through cytokines or viruses. Growing evidence associates Epstein-Barr virus (EBV) with Hodgkin's disease, a major issue being whether EBV is a passenger virus or has an aetiological role. This communication describes experimental conditions enabling observation of giant cell cytogenesis from peripheral blood mononuclear cells in culture. Mononuclear cells were isolated from autologous peripheral blood and cocultured with a single-cell suspension obtained from Hodgkin's lymph nodes in a culture chamber where the two cell populations are isolated by a microporous membrane that allows only cytokines and viruses to pass through. Under these experimental conditions, giant cells are formed in the peripheral blood mononuclear cell fraction; some of them appear morphologically indistinguishable from Reed-Sternberg cells and their mononuclear variant, while others much resemble Langhans giant cells. Some of these giant cells are positive for EBV DNA by in situ hybridization. These results suggest that an EBV-dependent biological activity is responsible for giant cell cytogenesis originating from lymphocytes and monocytes, induced either by EBV and/or cytokines.

Ia-antigen-T-cell interactions for a thymus-independent antigen composed of D amino acids

Synthetic polypeptide antigens of L amino acids, although bearing repeating sequences, are thymus-dependent (L-TD), whereas the same polymers composed of D amino acids are thymus-independent (D-TI), probably due to a slower rate of metabolism. Yet we found that lymph-node cells of BALB/c mice immunized with D-TI proliferate in response to it in vitro. To follow T-cell activation by D-TI, we established T-cell hybridomas to D-TI and to its analog composed of L isomers, L-TD, for comparison. The T-cell hybridomas express membrane alpha/beta T-cell receptors and secrete interleukin 2 upon stimulation with the respective antigen. In addition, D-TI-specific hybridomas are stimulated, to a lesser extent, by the L-TD antigen, whereas only some L-TD-specific hybridomas recognize D-TI. Moreover, biotinylated analogs of D-TI and L-TD bind to splenic antigen-presenting cells (APCs) from BALB/c mice. Binding is inhibited by an excess of nonbiotinylated L-TD, and by an excess of a peptide comprising residues 259-271 of the human acetylcholine receptor alpha subunit, which binds to I-Ad and I-Ed molecules without prior processing. Analysis of APC lysates following incubation of the APCs with biotinylated D-TI and L-TD reveals that the biotinylated antigen moiety is associated with Ia molecules. D-TI and L-TD bind to Ia molecules on intact APCs with similar KD values, 5 x 10(-8) M and 3 x 10(-8) M, respectively. However, D-TI has faster kinetics of binding than L-TD, probably due to different processing requirements. Hence, we have demonstrated a major histocompatibility complex class II-mediated T-cell response to a thymus-independent antigen.

A 39-kDa protein on activated helper T cells binds CD40 and transduces the signal for cognate activation of B cells

CD40 is a B-cell surface molecule that has been shown to induce B-cell growth upon ligation with monoclonal antibodies. This report shows that triggering via CD40 is essential for the activation of resting B cells by helper T cells (Th). A soluble fusion protein of CD40 and human immunoglobulin, CD40-Ig, inhibited the induction of B-cell cycle entry, proliferation, and differentiation by activated Th1 and Th2. The ligand for CD40 was identified as a 39-kDa membrane protein that was selectively expressed on activated Th. A monoclonal antibody specific for the 39-kDa protein inhibited CD40-Ig binding and also inhibited the activation of B cells by Th. These data indicate that the 39-kDa membrane protein expressed on activated Th is a binding protein for CD40 and functions to transduce the signal for Th-dependent B-cell activation.

HLA class-II-mediated homotypic aggregation: involvement of a protein tyrosine kinase and protein kinase C

Homotypic aggregation of B-lymphocytes, B-cell lines and class-II-positive T cells via HLA class II molecules was examined. Signaling via DR antigens induced rapid aggregation in a dose- and time-dependent manner, maximum and stable aggregation was induced within 20 minutes. On the contrary, rapid signaling via DP or DQ required prestimulation with either PMA or anti-sIg. Aggregation was temperature and energy dependent. [Ca2+] and [Mg2+] concentrations and an intact cytoskeleton were required while neither mRNA or protein synthesis were required. Furthermore, FACS analysis revealed that aggregation was not directly correlated with cell surface expression of HLA class II molecules. Our results demonstrate that aggregation was mediated through a protein tyrosine kinase (PTK)-dependent pathway that preceded activation of protein kinase C (PKC) and failure to generate either the PTK signal or the PKC signal prevented aggregation. The contribution of a tyrosine kinase was further demonstrated by the total inhibition of aggregation following treatment with an anti-CD45 mAb.

The B lymphocyte adhesion molecule CD22 interacts with leukocyte common antigen CD45RO on T cells and alpha 2-6 sialyltransferase, CD75, on B cells

Functional maturation of B lymphocytes correlates with expression of the B lineage-specific cell surface glycoprotein CD22. Two CD22 polypeptides have been characterized and suggested to play a role in B cell-B cell interaction as well as in B cell adhesion to monocytes. In this work we provide evidence that CD22 is directly involved in the cognate interaction between B and T cells. One of the two CD22 polypeptides, CD22 beta, interacts with a specific ligand on a subpopulation of CD4+ T cells. Our results suggest that the T cell ligand of CD22 is CD45RO, an isoform of the leukocyte common antigen class of phosphotyrosine phosphatases associated with the helper T cell phenotype. We further demonstrate that CD22 recognizes a second ligand, CD75, expressed predominantly on activated B cells and shown to be a cell surface alpha 2-6 sialyltransferase.

Differential activity of recombinant lymphokines on mouse B cell proliferation and cell cycle progression are revealed by 5-bromo-2'-deoxyuridine/Hoechst 33258 dye flow cytometry

Activation of resting mouse B cells with anti-mu chain antibodies (anti-mu) leads to cell proliferation. We have investigated the effect of recombinant T cell interleukins (IL 2 to IL 6) on such anti-mu-induced proliferation. No proliferative response was detected when IL 2, IL 3 and IL 6, either alone or in combination with anti-mu, were studied. Furthermore, neither IL 4 nor IL 5 could induce proliferation when added alone to B cell cultures. However, when combined with anti-mu, IL 4 as well as IL 5 stimulated cell growth. Analysis by 5-bromo-2'-deoxyuridine/Hoechst 33258 flow cytometry revealed distinct effects of IL 4 and IL 5 on B cell growth. In the presence of anti-mu, both IL 4 and IL 5 co-stimulated unfractionated splenic B cells. However, when B cells were separated into subpopulations by density, IL 4 proved to be a cell cycle progression factor, stimulating the majority of resting B cells to enter the cell cycle. In contrast, IL 5 had little effect on the resting fraction of B cells. Rather, IL 5 acted as a co-competence factor, stimulating predominantly low-density B cells. Following exposure of anti-mu alone, most B cells accumulated in the G1 of the second cycle. Upon addition of IL 4, the cells acquired the ability to progress into the next S phase compartment. Contrary to what is seen when B cells are stimulated by other mitogens, very few cells are in the G2 compartments after anti-mu plus IL 4 stimulation. This phenomenon was not due to a differential cell cycle progression rate. Our findings provide an analytical basis for fractionating cell-cycle-compartment-specific B cells for their molecular study.

Liposome adjuvanticity: influence of dose and protein:lipid ratio on the humoral response to encapsulated and surface-linked antigen

The humoral response to bovine serum albumin either encapsulated in or surface-linked to liposomes was studied as a function of dose and protein:lipid ratio. Total immunoglobulin, total IgG, IgM, and the G isotypes, IgG1, IgG2a, and IgG3 were measured during the plateau phase of production after a boosting injection. Although the adjuvant character of liposomes was confirmed regardless of the mode of antigen association, important differences in the response to the two types of liposomal formulations were observed. Our results suggest that surface-linked antigen stimulates the immune system at lower doses than its encapsulated counterpart, is more sensitive to the protein:lipid ratios, and can stimulate the production of particular immunoglobulin isotypes in controlled conditions. Our data support the idea that different pathways of processing are utilized by the two forms of liposomal antigen.

Antigen activation of human B lymphocytes bearing artificial antigen receptors

When highly purified human and murine B cells are challenged in vitro with certain so called "T cell-independent" activators such as the polyclonal B cell activator lipopolysaccharide (LPS) or the clonally specific B cell activator dinitrophenyl-conjugated polymerized flagellin (DNP-POL), mouse, but not human, cells differentiate into immunoglobulin-secreting cells. However, results from this study show that DNP-POL can cause human B cell differentiation in a T cell-independent manner when the antigen is concentrated onto the cells via artificially incorporated palmitate-modified anti-DNP mouse IgA molecules. This response is comparable in magnitude to that induced by a T cell-dependent polyclonal B cell activator, pokeweed mitogen, in unfractionated mononuclear cell cultures, suggesting that DNP-POL induced polyclonal B cell differentiation. DNP-POL binding to the artificial receptor molecules on B cells did not cause cellular proliferation, even in unfractionated mononuclear cell populations. These results are similar to those obtained in previous studies using mouse B cells in which the artificial receptor was unable to act as a transmembrane signaling element. From these studies, we conclude that B cells express clonally unrestricted, presumably low-avidity, endogenous receptor for POL, and that signaling through this receptor activates B cell differentiation but not cell proliferation.

Selective impairment of humoral immunity in feline leukemia virus-induced immunodeficiency

We used a panel of in vitro assays to investigate the nature of immune dysfunction in cats infected with FeLV-FAIDS, a naturally occurring, molecularly cloned feline leukemia virus (FeLV) isolate which induces a fatal immunodeficiency syndrome in infected cats. During the asymptomatic period preceding immunodeficiency disease, we were unable to detect any deficits in concanavalin A-induced blastogenesis, xenogeneic mixed-lymphocyte reaction assays, stimulation of lymphocytes by soluble protein antigen, and cytotoxic T lymphocyte assays. However, during this period humoral immune responses in the FeLV-FAIDS-infected cats were dramatically impaired. As early as 9 weeks after virus inoculation, the ability to mount either an IgM or IgG response to soluble protein antigens was lost. Neither B cell function, as assessed by lipopolysaccharide-induced blastogenesis or circulating B cell numbers, as assessed by immunofluorescence, differed between infected and control cats. These results suggest that FeLV-FAIDS infection may impair a subpopulation of T helper cells, that provides help for the production of antibody. Consistent with earlier observations of cats naturally infected with FeLV, our results indicate that early impairment of humoral immunity is an important component of the immunodeficiency syndrome induced by FeLV in cats.

Differential abilities of Th1 and Th2 to induce polyclonal B cell proliferation

Human gamma globulin-specific T helper cell (Th) clones, activated by HGG in the presence of antigen (Ag)-presenting cells, stimulated polyclonal B cell proliferation. Both Th1 and Th2 clones induced B cell proliferation, but Th1 clones were generally 5- to 10-fold less efficient than Th2 in this capacity. Th1 and Th2 each induced proliferation of both small and large B cells, although Th1 induced less B cell proliferation than Th2, regardless of B cell size. Th1-induced B cell proliferation was increased significantly by stimulating the Th1 clones with immobilized anti-CD3 mAb. The B cell response to Ag-activated Th1 clones was also increased by the addition of rIL-4 or culture supernatants from activated Th2 clones, and this enhancement was abolished by addition of anti-IL-4 mAb. The differential capacity of the Th subsets to stimulate B cells could not be attributed to differences in the degree of Ag-induced activation of the Th clones as reflected by Th proliferation or Th expression of activation markers, RL388 Ag, IL-2R, or TfR. Taken together the results suggest that even though Th1 and Th2 are similarly activated by Ag-presenting cells, Ag-activated Th2 interact more effectively with B cells than Ag-activated Th1. It is possible that inefficient interaction and subsequent intercellular signaling between Th1 and B cells results in inefficient Th1-induced B cell proliferation, and that this deficiency may be circumvented by signals (e.g., lymphokines) provided by Th2, or by the stimulation of Th1 with plate-bound anti-CD3 Ab rather than Ag.

Liposomal vaccine: influence of antigen association on the kinetics of the humoral response

The kinetics of the primary and secondary humoral responses to either encapsulated or surface-linked bovine serum albumin have been compared by measuring the production of specific total immunoglobulin, IgG and IgM at various times postimmunization. From our data it can be concluded that surface linkage is the best way to induce a rapid, intense and prolonged response which, in contrast to that induced by encapsulated BSA, is characterized by a low IgG/IgM ratio. The results are discussed in relation to the possible routes followed by the antigen depending on its mode of association with liposomes in the initiation of the humoral response. Our results suggest that liposomal vaccine may be designed to activate specific pathways of the immune network preferentially.

Serum IgG subclass antibody responses in children vaccinated with influenza virus antigens by live attenuated or inactivated vaccines

To ascertain whether live attenuated or inactivated vaccines can be considered equivalent, we examined the primary antibody response of children following vaccination with influenza virus antigens in three different formulations. Nine children received cold recombinant vaccine (CRV) containing A/Korea/82 (H3N2) and A/Dunedin/83 (H1N1) variants. Eight of these children responded to HA of the H3N2 subtype and the major portion of the elicited antibody was in the IgG1 subclass. Antibody of low titer in the IgG2 and IgG3 subclasses was detected in two and six serum specimens, respectively. Six of the nine children administered with CRV responded to the H1 antigen and only IgG1 antibody was detected. Serum specimens from eight children less than one year of age (5 less than 6 months of age) who had developed an antibody response to trivalent inactivated vaccine (TIV) vaccination were examined. High levels of IgG1 antibody to purified H3 were detected in all eight children. Low titers of antibody in IgG2 and IgG3 subclasses were detected in two and five children, respectively. Antibody responses to purified H1 showed a similar subclass distribution. In order to examine secondary response, eight children primed by immunization with TIV vaccine were subsequently given a single booster dose of purified hemagglutinin (HA) conjugated to diphtheria toxoid (HA-D). In 6/8 specimens antibody rises were detected to purified H3 and H1 antigens. Prior to the HA-D immunization, low levels of HA specific IgG1 antibody were detected in all serum specimens and vaccine induced responses were primarily of the IgG1 subclass.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative effect on humoral response of four different proteins covalently linked on BSA-containing liposomes

The humoral response to encapsulated BSA appears to be a classical TD antigen response with a high ratio of IgG to IgM, whereas that to covalently-linked antigen is more complex, characterized by an enhanced synthesis of IgM, leading to an equal production of IgM and IgG. In a recent paper, we observed that surface-linked Con A on BSA-containing liposomes changed the isotype distribution to encapsulated BSA so as to mimic the response to surface-linked antigen. In the present study, we compared the immune response to BSA in BALB/c mice immunized with the antigen encapsulated into liposomes coated with one of four different proteins: Con A, Myo, MSA, or PWM. The humoral response was analyzed by measurements of antibody production (total Ig, IgM, and IgG isotypes) on serum samples obtained by cardiac puncture. It can be concluded from our results that any surface-linked protein may affect the interaction between liposome-associated antigen and immunocompetent cells.

A substantial proportion of the adult BALB/c available B cell repertoire consists of multireactive B cells

A variety of studies have documented multireactive antibodies in both the preimmune and naturally activated repertoire, but the relationship of these primarily IgM multireactive antibodies to antigen-specific primary and secondary response antibodies is currently not defined. In order to characterize the BALB/c preimmunization specificity repertoire and the baseline of naturally activated antibodies from which the immune response to a specific antigen (hen egg-white lysozyme, HEL) develops, panels of polyclonally activated blast-derived hybridomas (BlAbs) and natural antibody hybridomas (NAbs) from the spleens of unimmunized mice were screened for binding to a panel of nine complex antigens. Over half of the IgM-secreting BlAbs produced antibodies that were antigen-reactive; of these, over half were multireactive, i.e. capable of binding more than one complex antigen. There was no bias towards self vs foreign or thymus-dependent vs thymus-independent antigens. The frequency of antigen-reactive NAbs was about half the frequency of antigen-reactive antibodies found among the BlAbs. However, over half of the antigen-reactive NAbs were also multireactive, and the reactivity profile within the antigen-reactive subset of NAbs was similar to that within the antigen-reactive subset of BlAbs. These results suggest that the available repertoire of adult spleen cells contains a high proportion of multireactive antibodies, and that a subset of the available repertoire is randomly activated, yielding a small proportion of natural antibodies which closely reflect a random sampling of the available repertoire. Although monospecific precursor cells are rare, monospecific IgM BlAbs were found for all antigens in the panel except staphylococcal nuclease and mouse IgG. Monospecific as well as multireactive HEL-binding BlAbs were found at frequencies comparable to other protein antigens in the panel, and HEL-reactive NAbs were also present. On the other hand, it has previously been shown that HEL-reactive IgM antibodies (including multireactive antibodies whose specificities include HEL) are rare or absent in both the primary and secondary response to HEL. This cannot be attributed to an absence of available precursor B cells, and most likely reflects an early recruitment of HEL-reactive clones into the peripheral B cell pool. The possibility that polyreactive B cells may serve as precursors for some HEL-specific IgG antibodies is discussed.

The effects of bacterial lipopolysaccharide, anti-receptor antibodies and recombinant interferon on mouse B cell cycle progression using 5-bromo-2'-deoxyuridine/Hoechst 33258 dye flow cytometry

Polyclonal stimulation of resting B cells with anti-antigen receptor antibodies [anti-IgM mu chain antibody (anti-mu)] or with bacterial lipopolysaccharide (LPS) stimulates a proportion of B cells to proliferate. Exposure of resting B cells to both LPS and anti-mu activates a larger population of resting B cells than either alone, suggesting a synergistic effect of these two stimuli. Although recombinant interferon (rIFN) either alone or in combination with anti-mu has no apparent proliferative activity (as measured by [3H]thymidine incorporation), application of 5-bromo-2'-deoxyuridine/Hoechst 33258 dye flow cytometry reveals a distinct effect of rIFN on B cell growth. In the presence of anti-mu plus LPS, rIFN causes the majority of B cells to enter the cell cycle (CC), but a subset of B cells remains in the resting stage. Another subset of B cells has extremely rapid CC transit times, with a CC duration of less than 10 h. These studies show that both anti-mu and LPS are competence factors (which move cells from the G0 phase to the G1 phase). LPS acts also as a CC progression factor, while rIFN is a CC potentiating factor.

Splenic B cells and antigen-specific B cells process anti-Ig in a similar manner

B lymphocytes can process and present antigen to T cells. However, the fate of native antigen after its binding to specific B cells, i.e., the intracellular events involved in the processing and recycling of the antigenic fragments to the cell surface for antigen presentation, are not well understood. In the present study, we demonstrate that murine B cells degrade anti-Ig molecules bound to their surface and release acid soluble fragments into the supernatant. We also demonstrate that the kinetics of this process are identical for anti-mu, anti-delta, and anti-light chain antibodies, indicating that both surface IgM and surface IgD are equally effective in binding antigen and directing its processing. We also describe the effects of azide, chloroquine, and irradiation on this process. To extend these studies to the processing of specifically bound antigen, we demonstrate that highly purified trinitrophenyl antigen-binding cells degrade anti-Ig molecules with the same kinetics as unpurified splenic B cells. Thus, this purified population provides a suitable model system for the analysis of antigen degradation by antigen-specific cells.

Antibody responses to hapten in thymectomized mice: extraordinarily pronounced deficiency in IgG1 production

The effect of thymectomy on the production of antibodies was studied by immunizing mice with hapten-carrier conjugates. Antibody responses were analysed with monoclonal antibody-based quantitative isotype-resolving assays. In spite of bone marrow reconstitution, irradiation without thymectomy caused a long-lasting relative deficiency in responsiveness to T-independent antigens. Even when no visible remnants of the thymus could be observed at the autopsy of thymectomized mice, there appeared to be a gradual recovery of antibody-forming capacity within 4 months, as assessed by the response to a T-dependent antigen. Therefore, some of the thymectomized mice had to be regarded as having recovered with respect to the helper T-cell effect. The antibody responses to T-dependent antigens were improved in all isotypes by a functional T-cell system, but the IgG isotypes seemed to benefit more than IgM. The most conspicuous deficit in antibody production in non-recovered thymectomized mice was observed in the T-dependent responses of the IgG1 isotype (2000-fold reduction in contrast to about 50- to 100-fold in IgG2a, IgG2b, and IgG3).

Interactions between receptors for interleukin 2 and interleukin 4 on lines of helper T cells (HT-2) and B lymphoma cells (BCL1)

IL-2 and IL-4 induce a synergistic proliferative response in HT-2 cells, suggesting that IL-2Rs and IL-4Rs may interact. The purpose of this study was to examine the effect of IL-4 on the expression and function of IL-2Rs. Preincubation of HT-2 and BCL1-3B3 cells with IL-4 for 60 min at 4 degrees C or 37 degrees C resulted in a partial decrease in the number, but not the affinity of high affinity IL-2Rs as evidenced by Scatchard analysis of binding data. The decrease in the number of high affinity receptors correlated with decreased internalization of IL-2. After preincubation with IL-4, crosslinking of 125I-IL-2 to high affinity IL-2Rs also demonstrated a approximately 50% reduction in the number of high affinity IL-2Rs. Another lymphokine, IL-1, which acts on HT-2 cells, had no measurable effect on the affinity or number of IL-2Rs. Taken together, these results indicate that IL-4 downregulates the expression of high affinity IL-2Rs on some cells. It is not known whether this occurs by a direct ligand-mediated receptor interaction, by the sharing of a common receptor subunit, or by interaction of the two receptors with another membrane molecule or cytoskeletal component.

Murine polyclonal T-lymphocyte activation induced by phytohemmagglutinin; differential lymphokine requirements of two unusual activation pathways defined by resistance to blockade by barium and by cyclosporin A

We have recently demonstrated that polyclonal T-cell activation induced by PHA defines an activation pathway which is resistant to blockade by barium (Ba2+) ions. Other modes of T-cell activation, including ConA-induced responses, are completely blocked by Ba2+, which seems to affect an early Ca2+-dependent step of T-cell activation, as determined by kinetic and competition experiments. In the present study, we have analysed the lymphokine requirements of Ba2+-resistant pathway of PHA-induced T-cell activation by means of functional blocking experiments with monoclonal antibodies (mAbs) directed against mouse IL-2 (mAb S4B6) and against mouse IL-4 (mAb 11B11). We found that Ba2+-resistant T-cell activation can be blocked by either S4B6 or 11B11. Thus, both IL-2 and IL-4 participate in Ba2+-resistant T-cell growth induced by PHA. In addition, we found that cyclosporin A (CsA) completely blocks T-cell activation induced by either ConA or by PHA plus Ba2+, but not T-cell activation induced by PHA in the absence of Ba2+, which is reduced by less than 50% in most experiments. This CsA-resistant proliferative component of the PHA response is, thus, distinct from the Ba2+-resistant response, and is carried out by proliferating T-cells. Although mAbs S4B6 and 11B11 are potent blockers of ConA-induced responses, they failed to block CsA-resistant T-cell growth induced by PHA. At the doses of CsA employed, no IL-2 and/or IL-4 activity could be detected in the supernatants of CsA-treated, PHA-stimulated T-cell cultures. The data indicate that this CsA-resistant pathway is both IL-2 and IL-4-independent. The lymphokine involved in this T-cell activation pathway remains to be identified.

Immune response to vaccination

Effective immune responses requires a synchronization of a number of different physiological and immunological events. Effective vaccines simulate natural invasion of the body by microbes or parasites. The route of administration of vaccines contributes to the effectiveness of preventing or controlling local or systemic infections. Immune responses to microbial agents usually involve more than one mechanism. For instance, toxins may be neutralized by a single antibody, while cellular interactions are required for destruction of more complex microorganisms. These systems have been illustrated in this review.

B cell-stimulating activity of lymphoid cell membrane fractions

We had previously found that a mutagenized subline of the mouse thymoma EL4 very efficiently stimulates B cells via direct cell-cell contact, thereby inducing the responsiveness of B cells to cytokines. In the present study, we investigated whether this effect could also be mediated by plasma membranes of EL4 (and other) cells. By equilibrium centrifugation of cell homogenates, four cell membrane fractions of different densities were obtained. These were tested for (a) stimulation of B cell proliferation in conjunction with EL4 supernatant as source of cytokines, and (b) enhancement of B cell proliferation at suboptimal concentration of lipopolysaccharide. It turned out that all membrane fractions from a variety of T lineage cells (mutant EL4, parent EL4, BW5147, P198 thymomas, normal T cells) and B lineage cells (BCL1 lymphoma, X63Ag8 cytoplasma, normal B cells) exhibited similar B cell stimulating activity in both assays. Interleukin 1 activity was not detected in the membrane fractions. Heat treatment abolished all activity showing that protein at least was involved. Either protease treatment or extraction with detergent abolished the activity of subcellular fractions rich in intracellular membranes but not that of fractions most enriched in surface membranes. Finally, erythrocyte membranes also displayed B cell-stimulating activity sensitive to protease and detergent extraction. In contrast, and in confirmation of a previous study, liver cell membrane was inhibitory in the B cell proliferation assay with lipopolysaccharide. In conclusion, the effects of cell membranes did not reflect the unique activity of intact mutant EL4 cells. However, with respect to our data it is conceivable that membrane proteins with relatively nonspecific activity and wide distribution among lymphoid cells could play a role in T cell help together with molecules specialized in cell adhesion and cell triggering.

Lymphokine-mediated regulation of the proliferative response of clones of T helper 1 and T helper 2 cells

Murine Th1 and Th2 subsets differ not only in the lymphokines they produce, but also functionally. It is not clear what factors influence the preferential activation of one subset versus the other and what regulatory interactions exist between them. The purpose of this study was to examine the effect of lymphokines produced by clones of Th1 cells (IL-2 and IFN-gamma), Th2 cells (IL-4), and APC (IL-1) on the proliferative response of Th1 and Th2 cells after antigenic stimulation. Activation of both types of clones in the presence of antigen and APC resulted in the acquisition of responsiveness to the proliferative effects of both IL-2 and IL-4, although Th2 cells were more responsive to IL-4 than Th1 cells. Responsiveness of Th1 and Th2 cells to both lymphokines decreased with time after initial antigenic activation; Th1 cells lost their responsiveness to IL-4 more rapidly and to IL-2 more slowly than Th2 cells. IFN-gamma partially inhibited the IL-2 and IL-4-mediated proliferation of Th2, but not Th1 cells. Although the presence of IL-1 was not required for the response of Th1 or Th2 cells to IL-4, its presence resulted in a synergistic effect with IL-2 or IL-4 in Th2 but not in Th1 cells. Both subsets responded to a mixture of IL-2 and IL-4 in synergistic fashion. Delayed addition and wash-out experiments indicated that both IL-2 and IL-4 had to be present simultaneously in order for synergy to occur. These results suggest that Th cell subsets might regulate each other via the lymphokines that they secrete and that the pathways of IL-2 and IL-4 mediated proliferation are interrelated.

Regulation of antibody isotype secretion by subsets of antigen-specific helper T cells

The regulation of the subclass of immunoglobulin secreted by B cells has been studied in vitro in polyclonal systems using mitogens, such as lipopolysaccharide (LPS), to bypass the requirement for cognate interaction between antigen-specific T and B cells. In these systems, interleukin-(IL)-4 induces the secretion of IgG1 (ref. 1) and IgE (ref. 2); IL-5 enhances the secretion of IgA, and interferon-gamma (IFN-gamma) enhances the secretion of IgG2a (ref. 5). Clones of murine TH cells can be divided into two subsets, TH1 and TH2 (ref. 6). Both subsets synthesize IL-3 and granulocyte-monocyte colony-stimulating factor (GM-CSF), but only TH1 clones produce IL-2, IFN-gamma, and lymphotoxin (LT) and TH2 clones produce IL-4 and IL-5 (ref. 7). We have examined the role of clones of antigen-specific TH1 and TH2 cells in the regulation of the subclasses of IgG antibody secreted by antigen-specific B cells. Our results show that both types of TH cells induce the secretion of IgM and IgG3, whereas clones of TH1 and TH2 cells specifically induce antigen-specific B cells to secrete IgG2a and IgG1, respectively. We also demonstrate that regulation of commitment to the secretion of a particular IgG isotype occurs in two distinct stages: cognate interaction between T and B cells and interaction between T-cell-derived lymphokines and B cells.

Differential ability of B cells specific for external vs. internal influenza virus proteins to respond to help from influenza virus-specific T-cell clones in vivo

When a helper T-cell (TH) clone specific for the hemagglutinin, neuraminidase, matrix protein, or nucleoprotein of influenza strain A/PR/8/34 is adoptively transferred to athymic mice 1 day after virus infection the anti-viral antibody response of the mouse is enhanced. This response is directed predominantly to the hemagglutinin and requires associative T-cell-B-cell interactions. Delaying transfer of the TH clone has three consequences: (i) the onset of the anti-hemagglutinin antibody response is delayed; (ii) the titer of the anti-hemagglutinin response is reduced; and (iii) the titer of the antibody in the response against the internal proteins, matrix protein and nucleoprotein, is enhanced upon transfer of matrix protein- or nucleoprotein-specific, but not hemagglutinin- or neuraminidase-specific, TH clones. Thus, there is a hierarchy of help: B cells recognizing viral surface components, hemagglutinin or neuraminidase, can receive help from TH clones specific for any of the major structural viral proteins. In contrast, B cells responding to internal viral components, matrix protein or nucleoprotein, are restricted to receiving help almost exclusively from TH clones with the same protein specificity. These observations suggest that, upon B-cell surface immunoglobulin-antigen interaction and uptake of intact virus, B cells specific for viral surface proteins process and present all major structural viral antigens, enabling the B cells to interact with TH clones specific for any virion protein. B cells recognizing internal viral components, which may be accessible to interaction with B-cell immunoglobulin receptors mainly as free proteins, would present only the protein for which they are specific and, thereby, receive help only from the TH clones of the same protein specificity.

T cell-replacing factor (TRF)/interleukin 5 (IL-5): molecular and functional properties

TRF has originally been defined as a T-cell-derived lymphokine that triggers activated B cells for a terminal differentiation into Ig-secreting cells. HPLC-purified TRF from Sup of a murine TRF-producing B151 cell is an acidic glycoprotein, exerts BCGF II activity and induces expression of IL-2 receptors. It does not show IL-1, IL-2, IL-3, BSF-1/IL-4, or IFN gamma activity. We prepared monoclonal TB13 and NC17 antibodies against HPLC-purified B151-TRF which are specific for and can inhibit TRF as well as BCFG II activity of B151-TRF. Moreover, TB13 as well as NC17 antibody can immunoprecipitate the 46 Kd molecule from B151 Sup which exerts TRF as well as BCGF II activity. Complementary DNA (pSP6K-mTRF23) encoding for murine TRF/IL-5 was cloned and its entire nucleotide sequences were determined. The murine TRF/IL-5 cDNA encodes 133 amino acids including N-terminal strongly hydrophobic regions. Secreted recombinant TRF/IL-5 (apparent m.w. of 46 Kd) has 113 amino acid residues and also comprises homodimers of a molecule with an apparent m.w. of 25 to 30 Kd. TRF/IL-5 mRNA is constitutively expressed in constitutively TRF-producing B151 and is inducible in some T cell lines upon stimulation with PMA or Con A. TRF/IL-5 mRNA is also expressed in Tbc-primed T cells upon the stimulation with PPD, whereas its expression is not effectively induced in non-primed spleen cells by stimulation with Con A or PMA plus calcium ionophore. The translation product of murine TRF/IL-5 cDNA triggers resting as well as activated (DNP-primed or LPS-stimulated) murine B cells for terminal differentiation into Ig-secreting cells (IgM, IgG1, or IgA) accompanied by increased mRNA expression for secreted forms of relevant Ig heavy chain (mu, gamma, or alpha). Among these, increases in the level of mu, and alpha-specific mRNA for the secreted form of IgM and IgA, respectively, are prominent. Moreover, TRF/IL-5 induces maturation of resting B cells into IgM-secreting cells. TRF/IL-5 promotes growth of activated B cells as well as BCL1 cells. TRF/IL-5 is, therefore, a growth as well as a differentiation inducing factor for B cells. Moreover, it induces functional IL-2 receptors on resting as well as activated B cells, besides TRF and BCGF II activities.(ABSTRACT TRUNCATED AT 400 WORDS)