Th1 and Th2 clones differ in their response to a tolerogenic signal.

Th1 and Th2 clones specific for human gamma globulin (HGG) were compared and shown to differ in terms of the effects of tolerance induction on Ag-induced proliferation and helper activity. In developing a method to induce tolerance, splenic APC that had been pulsed with HGG and then fixed with 0.15% paraformaldehyde (HGG-FAPC) were used as a means to present Ag to the Th clones in the absence of costimulatory signals. Both Th1 and Th2 clones recognized HGG-FAPC as evidenced by their ability to proliferate to HGG-FAPC. Unlike Th2, Th1 proliferated to HGG-FAPC only in the presence of T cell-depleted allogeneic spleen cells as a source of accessory cell signals. The inability of Th1 cells to proliferate in the absence of costimulatory signals was due to Ag-specific inactivation: Th1 clones preincubated with HGG-FAPC were unable to proliferate when recultured with HGG and irradiated APC. In contrast to Th1 clones, Th2 clones showed no decrease in their Ag-induced proliferative capacity after exposure to any concentration of HGG-FAPC. However, when examined by using a second assay system, that of providing help for anti-HGG antibody production by primed B cells, Th2 preincubated with HGG-FAPC were markedly inhibited (up to 90%) in their ability to provide help. Preincubation with HGG-FAPC also inhibited the helper activity of the one Th1 clone that was found to induce a significant secondary antibody response. Taken together, the results suggest that exposure of Th1 to tolerogen in the form of HGG-pulsed fixed APC inactivates Th1 proliferative capacity, and possibly Th1 helper activity as well. Exposure of Th2 cells to a tolerogen suppresses the mechanism by which the Th2 cells provide Ag-induced B cell help, but does not inhibit the mechanism by which they proliferate to HGG. Furthermore, the results define a model that incorporates Ag processing as well as Ag presentation in the induction of tolerance in vitro.     

Ability of tolerized Th1 and Th2 clones to stimulate B cell activation and cell cycle progression.

Tolerant and nontolerant murine Th1 and Th2 clones, specific for human gamma-globulin (HGG), were compared for their ability to promote cell cycle entry and progression by B cells in vitro. When stimulated with HGG, nontolerant Th1 and Th2 clones induced similar increases in B cell membrane MHC class II levels--a phenomenon associated with early B cell activation. Nontolerant Th1 and Th2 clones also induced B cell DNA synthesis, an event associated with subsequent G1 phase traversal, although Th2 cells were more efficient than Th1 cells in stimulating this activity. Exposure of Th clones to tolerogen in the form of HGG-pulsed chemically fixed APC inhibited the ability of Th1 clones, but not Th2 clones to promote polyclonal B cell DNA synthesis in HGG-stimulated secondary cultures. However, Th1 clones exposed to tolerogen did not lose their ability to increase the expression of MHC class II molecules on B cells in these cultures. These results indicate that tolerance induction does not inhibit the ability of Th1 clones promote B cell cycle progression. In contrast, exposure of Th2 cells to tolerogen does not inhibit significantly the ability of these cells to stimulate B cell cycle entry or progression.     

Membranes from both Th1 and Th2 T cell clones stimulate B cell proliferation and prepare B cells for lymphokine-induced differentiation to secrete Ig.

Plasma membranes from the mitogen-activated mouse Th2 cell clone D10.G4.1 have recently been shown to provide the cell contact-dependent signals necessary for the induction of small B cell proliferation. Together with the Th2-derived lymphokines IL-4 and IL-5, these membranes stimulate production of Ig isotypes identical to those produced when B cells were stimulated by intact Th2 cells. In contrast, Th1 clones are poor inducers of Ig production in vitro. This could be solely due to differences in the lymphokines released by Th1 and Th2 cells or to differences in the cell-cell contact signals delivered by activated Th1 and Th2 cells. We report that membranes from three different activated Th1 clones induced strong Ag-independent proliferation of small dense B cells. The level of B cell proliferation was enhanced approximately fourfold by the addition of lymphokine-containing supernatant from Con A-activated Th2 cells and was unaffected by any of the lymphokine-containing supernatants from Con A-activated Th1 clones. As with D10.G4.1 membranes, Th1 membranes alone induced B cell proliferation but not secretion of Ig. However, addition of supernatant from Con A-activated D10.G41 cells, but not any supernatants from Con A-activated Th1 cells, induced Ig secretion of all isotypes. These effects were shown to not simply result from increased B cell numbers after stimulation with Th2 lymphokines. Thus, Th1 cell clones seem to poorly induce antibody responses entirely because of their lymphokine repertoire and not because of differences or deficiencies in the ability of these cells to deliver cell contact-dependent signals to B cells.     

B cell chemoattractant CXCL13 is preferentially expressed by human Th17 cell clones

Th 17 cells represent a novel subset of CD4+ T cells that have a protective effect against extracellular microbes, while they are also responsible for autoimmune disorders in mice. However, the protein expression profile of Th17 cells remains to be clarified. In this study, we report an effective method to establish human allo-reactive Th17 cell clones and demonstrate that human Th17, but not Th1 or Th2, cells express B cell chemoattractant CXCL13, by using DNA chips, RT-PCR, and ELISA. Such a pattern was also the case in Candida albicans-specific Th17 clones and synovial fluid specimens obtained from patients with rheumatoid arthritis. The biological implication of this finding is discussed.     

Accessory cell function of Th2 clones

We have investigated the ability of T helper clones to serve as accessory cells and in the presence of mitogen activate freshly-isolated, splenic T cells. In this type of costimulatory assay, the Th cells that secrete IL-4 but not the Th cells that secrete IL-2 function as AC to induce T cell proliferation in the presence of various T cell mitogens (Con A, anti-CD3 mAb, anti-TCR mAb, and anti-Thy-1 mAb). The signal provided by the accessory Th2 cells occurred independently of MHC restriction, and the analysis of dose-response curves showed the involvement of a single stimulator cell. CD4, as well as CD8 expressing splenic T cells were induced to proliferate by the Th2 clones and mitogen, but mAb specific for CD4 or CD8 failed to affect the response. These findings indicate that cloned Th2 cells functioned as accessory cells and induced naive T cells to proliferate in the presence of mitogen.     

Murine Th1 and Th2 clones proliferate optimally in response to distinct antigen-presenting cell populations.

We recently have devised a method for the derivation of OVA-specific Th1 and Th2 clones from the same primed lymph node cell preparation. Using a panel of such cells, we have examined the ability of distinct APC populations to stimulate proliferation of Th1 and Th2 clones. Both subsets proliferated well in response to OVA in the presence of whole spleen cells. However, purified B cells stimulated optimal proliferation of Th2 clones, whereas adherent cells stimulated optimal proliferation of Th1 clones. The proliferative response of Th2 cells stimulated with spleen cells irradiated with 3300 rad was dramatically less than that observed in response to spleen cells treated with 1000 rad; Th1 clones responded similarly to spleen cells exposed to either irradiation dose. Differential activation of Th1 and Th2 clones did not correlate with MHC-restricting element, or susceptibility to inhibition by mAb directed against CD4 or LFA-1. Lymphokine production by each subset still occurred under conditions of suboptimal proliferation, suggesting that the appropriate Ag processing and presentation events had transpired. The same pattern of response was observed using a specific OVA peptide that does not require processing, suggesting that differential responsiveness of Th1 and Th2 clones to different APC populations is not a result of defective Ag processing. Neither rIL-1 nor rIL-6 restored optimal proliferation of either subset. Our results suggest that unique cofactors are necessary for the optimal proliferation of Th1 and Th2 clones, and that these cofactors are produced by specialized APC populations.     

Induction of antigen-specific antibody responses in primed and unprimed B cells. Functional heterogeneity among Th1 and Th2 T cell clones

CD4+ T cells have been recently divided into two subsets. The functions of these subsets are thought to be distinct: one subset (Th1) is responsible for delayed type hypersensitivity responses and another (Th2) is primarily responsible for induction of antibody synthesis. To more precisely define the roles of both subsets in humoral immune responses, we examined the ability of a panel of nominal antigen specific Th1 and Th2 clones to induce anti-TNP specific antibody synthesis in TNP-primed or unprimed B cells. Four of nine Th1 clones induced little or no antibody synthesis with TNP-primed B cells. However, five other Th1 clones were very effective at inducing IgG anti-TNP plaque-forming cell (PFC) responses in primed B cells. One of these Th1 clones was analysed in detail and found to also provide helper function for unprimed B cells. Cognate B-T cell interaction was required for induction of both primary and secondary responses with this clone, indicating that a Th1 clone could function as a "classical" Th cell. The seven IL-4 producing Th2 clones examined were also heterogeneous in their ability to induce antibody secretion by TNP-primed B cells. Although four of the Th2 clones induced IgG and IgM anti-TNP PFC responses, two Th2 clones induced only IgM and no IgG antibody, and another clone failed to induce any anti-TNP PFC. All Th2 clones failed to induce any anti-TNP PFC. All Th2 clones produced high levels of IL-4, but "helper" Th2 clones produced significantly greater amounts of IL-5 than "non-helper" Th2 clones. These studies indicate that some IL-2- and some IL-4-producing T cell clones can induce TNP-specific antibody in cell clones can induce TNP-specific antibody in primed and unprimed B cells, and that Th1 and Th2 clones are heterogeneous in their ability to induce Ig synthesis. Therefore, although T cell clones can be classified as Th1 or Th2 types according to patterns of IL-2, IFN-gamma, or IL-4 synthesis, the functional capacity to induce antibody synthesis cannot be predicted solely by their ability to secrete these lymphokines.     

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.     

Expression of specific clones during B cell development.

The expression of DNP- and TNP-specific B cells in spleens of neonatal BALB/c mice was analyzed by the in vitro splenic focus technique. B cells of these specificities were found to be present in slightly higher frequency in neonatal than in adult spleens. The parameters of stimulation of neonatal B cells were similar to those of adult B cells but the antibody-forming cell progeny of neonatal B cells produce predominantly gammaM rather than gammaG antibody and produce less antibody than the progeny of adult B cells. Isoelectric focusing analyses of monoclonal antibodies derived from neonatal B cells stimulated in vitro with DNP or TNP revealed that over 90 per cent of the antibodies could be identified as belonging to one of six predominant clonotypes, three specific for DNP and three for TNP. While individual neonates rarely expressed all of the predominant clonotypes, B cells of each of the six clonotypes were found in several donors. When B cells of a given predominant clonotype were present in an individual many such B cells could be found and in many cases the entire DNP- or TNP-specific B cell population of an individual could be accounted for by B cells of a single clonotype. These findings are discussed in terms of the diversity of clonotype specificities available in neonates, the kinetics of development of cells within a clonotype, and factors that may play a role in controlling the expression of B cell clones.     

B cell antigen presentation promotes Th2 responses and immunopathology during chronic allergic lung disease

Background

The role of B cells in allergic asthma remains undefined. One mechanism by which B cells clearly contribute to allergic disease is via the production of specific immunoglobulin, and especially IgE. Cognate interactions with specific T cells result in T cell help for B cells, resulting in differentiation and immunoglobulin secretion. Proximal to (and required for) T cell-dependent immunoglobulin production, however, is antigen presentation by B cells. While interaction with T cells clearly has implications for B cell function and differentiation, this study investigated the role that B cells have in shaping the T cell response during chronic allergic lung disease.

Methodology/Principal Findings

In these studies, we used a clinically relevant mouse model of chronic allergic lung disease to study the role of B cells and B cell antigen presentation in this disease. In these studies we present several novel findings: 1) Lung B cells from chronically allergen challenged mice up-regulated MHC II and costimulatory molecules CD40, CD80 and CD86. 2) Using in vitro studies, B cells from the lungs of allergen challenged mice could present antigen to T cells, as assessed by T cell proliferation and the preferential production of Th2 cytokines. 3) Following chronic allergen challenge, the levels of Th2 cytokines IL-4 and IL-5 in the lungs and airways were significantly attenuated in B cell −/− mice, relative to controls. 4) B cell driven Th2 responses and mucus hyper secretion in the lungs were dependent upon MHC II expression by B cells.

Conclusions/Significance

Collectively, these results provide evidence for antigen presentation as a novel mechanism by which B cells contribute to chronic allergic disease. These findings give new insight into the mechanisms by which B cells promote asthma and other chronic diseases.     

Ocular immune privilege promoted by the presentation of peptide on tolerogenic B cells in the spleen. II. Evidence for presentation by Qa-1

Ocular immune privilege is the result of several unique features of the eye, including the systemic down-regulation of Th1 immune responses to Ags encountered in the anterior chamber of the eye-a phenomenon termed anterior chamber-associated immune deviation (ACAID). The induction of ACAID requires the participation of three cell populations: the ocular ACAID APC, the splenic B cell, and the splenic T cell. Because B cells have been implicated in tolerogenic Ag presentation in other systems, we hypothesized that B cells were responsible for the induction of regulatory T cells in ACAID. The central hypothesis for this study is that APC from the eye migrate to the spleen where they release antigenic peptides (OVA) that are captured and presented to T cells by splenic B cells. A combination of in vitro and in vivo studies demonstrated that splenic B cells, incubated with ACAID APC in vitro, were capable of inducing ACAID when transferred to naive mice. The induction of ACAID required the normal expression of ss(2)-microglobulin on both the B cell and ACAID APC, but not on the T suppressor cells. Moreover, the induction of ACAID regulatory cells required histocompatibility between the B cells and regulatory T cells at the TL/Qa region. The results indicate that: 1) B cells are necessary for the induction of ACAID; 2) ACAID B cells do not directly suppress the expression of delayed-type hypersensitivity; and 3) the induction of Ag-specific regulatory T cells by ACAID B cells requires histocompatibility at the TL/Qa region.     

Effects of tolerance induction on early cell cycle progression by Th1 clones.

Human gamma-globulin (HGG)-specific mouse Th1 clones exposed to tolerogenic signals provided by HGG-pulsed paraformaldehyde-fixed splenocytes (HGG-FAPC) were analyzed for antigen-induced progression through the early phases of the cell cycle. Exposure of Th1 clones to HGG-FAPC in primary cultures inhibits the ability of the clones to synthesize DNA in response to HGG and normal APC in secondary cultures. The Th1 clones in these secondary cultures were found to be blocked in G1a phase as evidenced by cell cycle analysis and by reduced numbers of cells expressing high levels of IL-2R and TfR. This cell cycle blockade of Th1 cells was not observed if the secondary cultures were stimulated with IL-2-containing Con A CM instead of antigen. These data suggest that in our system the inhibition in antigen-induced cell cycle progression associated with Th1 tolerance induction occurs at the G1a/G1b phase transition.     

Anti-CD3 antibody induces unresponsiveness to IL-2 in Th1 clones but not in Th2 clones

Culture of murine T cells with immobilized (platebound) anti-CD3 antibody results in autocrine growth factor secretion in both Th1 (IL-2 producing) and Th2 (IL-4 producing) cells. Using a panel of murine T cell clones, we demonstrate that the IL-2-induced proliferation of Th1 clones is dramatically inhibited by immobilized anti-CD3 antibody, whereas that of Th2 clones is not. This unresponsiveness of Th1 clones to IL-2 is not due to decreases in IL-2R expression. Supernatants from Th1 or Th2 cell cultures fail to alter the effects of anti-CD3 on the two types of clones, suggesting that unresponsiveness induced in Th1 clones or the lack thereof in Th2 clones is not mediated by a stable cytokine(s). Accessory cells enhance the proliferation of Th1 cells exposed to low concentrations of anti-CD3, but the unresponsiveness induced by high concentrations of anti-CD3 is not prevented by accessory cells. Finally, soluble anti-CD4 antibody prevents the induction of the unresponsive state even at high concentrations of anti-CD3. These experiments demonstrate that two subsets of cloned CD4+ T cells differ in their responses to anti-CD3, and that CD4 molecules may play a critical role in regulating the outcome of receptor-mediated stimulation.     

Th1 and Th2 cell clones to a poorly immunogenic tumor antigen initiate CD8+ T cell-dependent tumor eradication in vivo

Although CD8(+) T cells play a central role as immune effectors, CD4(+) T cells act to control the activation and persistence of the CD8(+) T cell response in autoimmune disease, antiviral immunity, and experimental systems with immunogenic model tumor Ag. However, little information is available on the effects of CD4(+) T cells on the function of endogenous CD8(+) T lymphocytes recognizing authentic tumor rejection Ag with limited immunogenicity. We report here that the prophylactic or postchallenge administration of T helper Th1-type and Th2-type CD4(+) clones specific for an unmutated rejection Ag (murine P815AB, resembling tumor-specific shared Ag in humans) leads to the induction of P815AB-specific reactivity in vivo and concomitant tumor destruction, with quantitative rather than qualitative differences characterizing the antitumor activity of Th1 vs Th2 cells. Because the transferred CD4(+) cells lacked direct antitumor activity in vitro and required the de novo generation of P815AB-specific CD8(+) T cells in vivo, these findings suggest that CD4(+) lymphocytes can enhance the ability of host APC to initiate an endogenous CD8(+) T cell response to authentic, poorly immunogenic tumor rejection Ag.     

Heterogeneity of helper/inducer T lymphocytes. IV. Stimulation of resting and activated B cells by Th1 and Th2 clones

To test the hypothesis that resting and previously activated B lymphocytes differ in their proliferative and differentiative responses to various Th cell-derived stimuli, we have examined the interactions of purified small (resting) and large (activated) murine B cells with rabbit Ig-specific Th1 and Th2 clones in the presence of the Ag analogue, rabbit anti-mouse Ig antibody. Small numbers of Th2 cells induce strong Ag-dependent proliferation of and Ig secretion by both resting and activated B lymphocytes. In contrast, Th1 clones stimulate lower responses of activated B cells and fail to stimulate small resting B cells. An interaction with Th1 clones does make small B cells responsive to the Th2-derived cytokine, IL-4, indicating that Th1 clones are capable of delivering some but not all the stimuli necessary for the induction of humoral immunity. Finally, in order to compare the responses of small and large B cells to cognate interactions and secreted cytokines, we used an autoreactive I-Ak-specific Th2 line. This line induces proliferation of and Ig secretion by I-Ak expressing but not H-2d resting and activated B cells as a result of cognate interactions. However, when the H-2d B cells are bystanders in the presence of cytokine secretion by this Th2 line, or are directly exposed to Th2-derived cytokines, both small and large B cells are induced to proliferate but only the large B cells secrete antibody. These results indicate that the magnitude and nature of antibody responses depend on three principal factors: the cytokines produced by Th cells, the state of activation of the responding B lymphocytes, and whether the B cells are recipients of cognate help or are bystanders at the site of T cell stimulation. Our findings also confirm the view that cognate T-B interactions are most efficient for initiating B cell responses and may allow B cells to subsequently respond to a variety of T cell-derived cytokines.     

The use of specific helper T cell clones to study the regulation of isotype expression by antigen-stimulated B cell clones

In order to determine the mechanism by which helper T cells regulate the production of the various immunoglobulin (Ig) classes, a number of helper T cell clones specific for keyhole limpet hemocyanin (KLH) were generated. These helper T cell clones then were used in a modified splenic fragment system whereby cloned helper T cells and a source of B cells were limit-diluted into naive, lethally irradiated recipients. The B cell clones that were subsequently stimulated in such an assay system by the addition of the antigen 2,4-dinitrophenol (DNP)-KLH then were tested for the various isotypes produced. The results of these studies indicate that the use of a single helper T cell clone could result in the production of all known Ig isotypes including IgE. Moreover, the use of a single helper T cell clone could result in multiple isotype production by a single B cell clone. However, a comparison of the isotypes secreted by a number of different B cell clones that were stimulated with the same helper T cell clone indicated that a variety of isotypic patterns could be obtained. In addition, it was found that the majority of B cell clones produced in the presence of T cell clones secrete fewer numbers of different isotypes compared with B cell clones generated with a heterogeneous population of T cells. Finally, no evidence could be found for isotype-specific helper T cell clones, although a few of the T cell clones appeared to induce a somewhat restricted isotype pattern in which only two or three different isotypes were observed.     

Heterogeneity of B cell clones: immunoglobulin-secreting subsets

Staphylococcus aureus Cowan I bacteria (SpA CoI) is known to be a polyclonal B-cell activator of human lymphocytes. In this study, we investigated which of the B-cell subsets SpA CoI could stimulate and induce immunoglobulin (Ig) production. B-Cell subsets were separated from peripheral blood and tonsil lymphocytes by rosette formation with E, EA_IgG, EAC, anti-Ig-conjugated ox erythrocytes (OE-anti-Ig), and protein A-conjugated OE (OE-Pro A), or on a bovine serum albumin (BSA) discontinuous density gradient. The cells responding to SpA CoI included E^?, C3 receptor-positive (C3R⁺), Fc receptor-negative (FcR^?), and surface Ig-positive (SIg⁺) B-cell subsets. These B-cell populations responded well to SpA CoI and produced significant amounts of IgG, IgM, and a lesser amount of IgA. Among SIg⁺ B cells, IgG, IgA, and IgM⁺ B-cell subsets responded to SpA CoI and produced large amounts of Ig belonging to each corresponding Ig class. IgD⁺ B cells failed to produce Ig of any class, except for minimal amounts of IgG and IgM. While both the protein A receptor-positive (Pro A · R⁺) and negative (Pro A · R^?) cells responded well to SpA CoI, Pro A · R⁺ B cells produced IgG mainly and Pro A · R^? B cells produced IgM. Fractionation of B cells on a BSA gradient revealed that comparatively small-sized and denser B-cell subsets responded well to SpA CoI and produced every class of Ig.     

Heterogeneity of signal requirements in T cell activation within a panel of human proliferative T cell clones

Activation of T lymphocytes is initiated by receptor ligand interactions at the cell surface leading to the transduction of intracellular signals followed by the de novo synthesis and expression of T cell activation markers (including receptors for interleukin 2 (IL 2) and transferrin), production of lymphokines, and T cell proliferation. This requisite first step for activation of T lymphocytes can be mimicked in certain situations with a variety of stimuli. These include antibodies to certain integral membrane proteins, phorbol esters, and plant lectins that act as mitogens. In this paper, we report that at least two classes of human T cell clones can be distinguished based upon signal requirements necessary to induce proliferation. Although all clones analyzed expressed IL 2 receptors and secreted IL 2 after non-antigenic activation, one subset of clones did not proliferate in response to the same non-antigenic signals. In that subset, complete activation leading to proliferation required interaction of the T cell with specific antigen. The ability to subset these T cell clones into two groups did not correlate with phenotypic differences, source of the clone, nor with magnitude of intracellular calcium mobilization. By studying the stimulation requirements of these two subsets of human T cell clones through the use of specific antigen or antigen-independent stimuli, it was possible to demonstrate that different stimuli varied in their ability to induce steps of T cell activation. Analysis of reactivity of these clones to suboptimal stimulation allowed the definition of intermediate stages of T cell activation. Such intermediate stages might reflect a diversity of intracellular signaling pathways or a complexity of regulatory mechanisms distal to the events that allow intracellular calcium mobilization. Thus for the first time, it has been possible to study ordered events of T cell activation in non-transformed, antigen-dependent human T lymphocytes. The data presented in this paper suggest that T cell activation is not an all or nothing phenomenon, and there is an ordered sequence of events that can be differentiated based upon signal requirements at the T cell membrane.     

Collaboration of Th1 and Th2 T cell clones in specific antibody responses: regulation of the IgM response to phosphorylcholine

Carrier (KLH)-specific type 1 T cell clones (Th1), which are defined by secretion of IL-2 and IFN-gamma but not IL-4, and type 2 (Th2) clones, which secrete IL-4, but not IL-2 or IFN-gamma, have been isolated and analyzed for their ability to collaborate in providing help for B cells to secrete phosphorylcholine-specific IgM antibodies. The resulting antibody responses exhibited a characteristic pattern suggesting two distinct regulatory interactions among the Th1, Th2, and B cells. At low doses of antigen, Th1 cells enhanced the helper function of the Th2 cells, an effect due primarily to IL-2. At high doses of antigen, Th1 cells or IFN-gamma inhibited Th2-dependent antibody responses. The inhibitory effect of Th1 or IFN-gamma affected primarily the hapten-carrier-linked portion of the response. The overall effect was a modulation of the antigen dose-response curve for antibody production, eliminating the sharp increases in dose response mediated by isolated T cell clones. The data suggest that collaborative interactions of Th1 and Th2 cells in antibody production may have important physiological consequences.