Lyb-5+ B cells can be activated by major histocompatibility complex-restricted as well as unrestricted activation pathways

It has previously been demonstrated that B cells can be activated through two distinct T helper (Th) cell-dependent pathways, one requiring both carrier-hapten linkage and MHC-restricted T-B interaction and the other requiring neither. In addition, it has been shown that different B cell subpopulations exist and that these subpopulations differ in their activation requirements. Previous studies demonstrated that resting B cells containing an Lyb-5+ subpopulation were activated by MHC-unrestricted T cell signals, whereas resting Lyb-5- B cells were activated only through MHC-restricted T-B interaction. It was suggested that this difference resulted from the ability of Lyb-5+ but not Lyb-5-B cells to respond to soluble MHC-unrestricted Th signals. Because Lyb-5+ B cells were responsive in these previous experiments to MHC-unrestricted Th signals, it could not be determined whether Lyb-5+ B cells were also responsive to MHC-restricted Th signals. Consequently, the present study was undertaken to directly address the question of whether Lyb-5+ B cells can be activated under appropriate conditions by MHC-restricted as well as unrestricted T cell-B cell interactions. It was found that unprimed normal B cells (containing Lyb-5+ and Lyb-5-B cells) but not unprimed xid-defective populations (Lyb-5- only) can be activated by cloned KLH-specific and MHC-restricted Th cells in response to either high or low concentrations of TNP-KLH. The IgM response of Lyb-5+-containing B cells to a high concentration of antigen (10 micrograms/ml) was MHC unrestricted, whereas the IgM response of unprimed Lyb-5+ B cells to a low concentration of antigen (0.001 micrograms/ml) was MHC restricted. Thus, unprimed Lyb-5+ B cells can be activated through both MHC-restricted and unrestricted pathways. It was further demonstrated that the activation requirements of Lyb-5+ and Lyb-5- B cells differed even for MHC-restricted B cell activation.     

Streptococcal serotype carbohydrate represents a novel class of type 2 antigen which is T-independent

Our studies reported here, fully characterize two unique type 2 antigens trinitrophenol (TNP)-M1 serotype carbohydrates (TNP-M1 g and TNP-M1 c) derived from streptococci, which fail to induce antibody responses in xid or neonatal mouse splenic cultures. These antigens generate brisk responses in normal spleen and Peyer's patch cell cultures of xid mice, all of which suggest that responses are elicited in the Lyb-3+, 5+ B subpopulation. The antibody responses to TNP-M1 g (and TNP-M1 c) are not dependent upon T cells. Furthermore, TNP-M1 carbohydrates induce anti-TNP plaque-forming (PFC) responses in cultures of small, resting splenic B cell populations without an added T cell requirement. Thus two categories of type 2 antigens are distinguished, one which requires T cells or derived factors, e.g., TNP-Ficoll, and a second TNP-carbohydrate antigen TNP-M1 that does not. Studies of the mitogenic and polyclonal B cell activation properties of M1 carbohydrates indicated that B cell proliferation is induced in both xid (Lyb-3-, 5-) and normal (Lyb-3-, 5- and Lyb-3+, 5+) splenic B cell subpopulations, but that differentiation to IgM synthesis fails to occur in the Lyb-3-, 5- B cell subpopulation. Thus M1 carbohydrates are unique probes that allow the selective induction of proliferation and differentiation of mature B cells that are presumably Lyb-3+, 5+. Because the M1 serotype carbohydrates induce polyclonal IgM synthesis and antigen-specific responses in only the mature B cell population in the absence of T cells, whereas TNP-Ficoll and other type 2 antigens require T cells or their derived factors, the Lyb-3+, 5+ B cell subpopulation may consist of a T cell-dependent and a T cell-independent compartment for responses to different carbohydrate type 2 antigens.     

IgM induction in murine B hybridomas with Ia-restricted T cell clones: a monoclonal model for T and B cell interactions in antibody response

The mechanism of MHC-restricted T and B cell interactions in antibody response was studied with IgM-inducible B hybridomas and antigen-specific helper T cell clones. B hybridomas were prepared by fusion between splenic B cells from (CBA/N (H-2k) X BALB/c (H-2d)) F1 (NBF1) male mice and a B lymphoma cell line, M12.4.5. A B hybridoma clone, 1M70, which expressed I-Ad but not I-Ak determinants was chosen in the present study. IgM secretion was induced in 1M70 when it was cocultured with a "resting" KLH-specific and H-2d restricted helper T cell clone in the presence of KLH. A "resting" KLH-specific and H-2k restricted T cell clone did not induce IgM secretion in 1M70 even in the presence of KLH. However, when these KLH-specific T cell clones were activated by KLH and appropriate antigen presenting cells, both H-2d and H-2k restricted T cell clones induced IgM secretion in 1M70 even in the absence of KLH. A monoclonal anti-I-Ad antibody inhibited IgM secretion induced by a "resting" H-2d restricted T cell clone, but not by an "activated" T cell clone. These results indicated that T cell clones recognized antigens in the context of Ia molecules on B hybridomas in a MHC-restricted manner and were activated to produce B cell stimulatory factors which in turn acted on B hybridomas in a non-MHC-restricted manner and induced differentiation of B hybridomas into IgM secreting cells.     

T cell regulation of B cell activation. An antigen-mediated tripartite interaction of Ts cells, Th cells, and B cells is required for suppression

To determine the requirements underlying the antigen specificity observed in T cell-mediated immune response suppression, cloned major histocompatibility complex (MHC)-restricted T suppressor (Ts) cells specific for keyhole limpet hemocyanin (KLH) and cloned MHC-restricted T helper (Th) cells specific for fowl gamma-globulin (FGG) were employed to study the regulation of trinitrophenyl (TNP)-specific B cell responses. Neither antigen bridging between Ts cells and Th cells (FGG=KLH) nor bridging between Ts cells and B cells (TNP-KLH) was sufficient to allow suppression; a mixture of FGG=KLH and TNP-KLH was also insufficient for suppression. In contrast, suppression was induced by KLH-specific Ts cells only when suppressor determinants (KLH), helper determinants (FGG), and B cell determinants (TNP) were covalently linked on the same molecule (TMP-FGG)=(TNP-KLH) or TNP-(FGG=KLH)). These findings imply that a tripartite antigen-mediated interaction of Ts cells, Th cells, and responding B cells is necessary for the mediation of this antigen-specific suppression.     

Clonal analysis of antigen-specific interactions between T cells and genetically engineered B cells

In order to investigate T cell-B cell interactions we constructed monoclonal, antigen-specific T- and B-cell populations. The Ia+ B-cell lymphoma A20-2J was transfected with trinitrophenyl (TNP)-specific heavy (mu) and light (kappa) chain Ig genes. A hapten-carrier complex (TNP-keyhole limpet hemocyanin (KLH)) bound to the surface Ig expressed on the transfectant and was presented to carrier-specific T-cell hybridoma clones at markedly low doses of antigen (0.01 microgram/ml) and in an Ia-restricted fashion. Two responses were elicited in the responding T-cell clones: (i) high levels of IL-2 secretion (320 units/ml), and (ii) cytotoxicity directed against the antigen-presenting B cell. This cytotoxicity was inhibited by D-mannose and was directed against innocent bystander cells, unlike cytotoxicity mediated by NK cells or alloreactive cytotoxic T lymphocyte. Helper and cytotoxic functions were often present in different T-cell hybridomas but some clones exhibited both activities. One representative T-cell hybridoma exhibited strong helper function for TNP-primed splenic B cells as detected in a plaque-forming cell assay, but was cytotoxic toward antigen-presenting B cells. Such monoclonal assay systems for studying cognate interactions of heterogeneous T cells and specific antigen-presenting cells will provide us with valuable new approaches for the study of antigen-specific T-cell regulation of B-cell activation in immune responses.     

T cell regulation of B cell activation: antigen-specific and antigen-nonspecific suppressor pathways are mediated by distinct T cell subpopulations

The present studies were carried out to characterize the cellular events involved in the induction and function of carrier-specific Ts cells, which selectively regulate the generation of IgG responses by Lyb-5- B cells. It was demonstrated that this regulation is in fact mediated by two distinct suppressor pathways. In one pathway, carrier-primed Lyt-1 + 2 - Ts cells are specifically activated by in vitro reexposure to the priming antigen. After this specific activation, these Lyt-1 + 2 - Ts cells are able to suppress IgG responses in an antigen-nonspecific manner. This suppression requires the participation of unprimed Lyt-1 - 2 + T cells, and is effective in both the early and the late phases of antibody responses. A second suppressor pathway requires the antigen-specific activation of primed Lyt-1 - 2 + Ts cells. Suppression of antibody responses by activated Lyt-1 - 2 + Ts cells is highly carrier specific, in contrast to the nonspecific effector function of Lyt-1 + 2 - Ts cells, appears to act without requirement for additional T cell populations; and is effective only early in the course of the antibody response. Thus, it appears that two Ts cell populations may function through distinct mechanisms to regulate the generation of IgG Lyb-5- B cell responses.     

Clonal analysis of H-2Kb + TNP recognition by T cells with the use of H-2Kbm mutants and H-2Kb-specific monoclonal antibodies

Eleven long-term cytotoxic T lymphocyte (CTL) clones derived from C57BL/10 T cells sensitized in vivo and in vitro with trinitrobenzene sulfonate- (TNBS) treated syngeneic cells were all restricted to the K end of H-2b. The fine specificity of these CTL clones was analyzed by using H-2Kbm mutant target cells and H-2Kb-specific monoclonal antibodies (mAb). Seven distinct patterns of reactivity of the T cell clones could be observed with the use of six H-2Kbm mutant target cells. Further heterogeneity could be detected in terms of the ability of anti-Lyt-2 mAb to inhibit CTL activity. Cross-reactivity between H-2Kb + TNP and H-2Kbm + TNP was observed for all clones tested for bm5 and bm6, but less frequently for bm3 (8/11), bm8 (7/10), bm4 (4/11), and bm1 (3/11). It was further observed that amino acid substitutions located in the first domain only (one clone), or in the second domain only (six clones), or in either the first or the second domain (three clones) of the H-2Kb molecule could affect target cell recognition by a given T cell clone. the latter type of reactivity suggested that some clones recognized "conformational" determinants of the H-2 molecule, or that amino acid substitutions in one domain might influence the structure of the next domain. One H-2Kb + TNP-reactive clone exhibited a heteroclitic behavior with decreasing avidities for target cells expressing H-2Kbm8 + TNP, H-2Kb + TNP, and H-2Kbm8, which further extends the various patterns of T cell cross-reactions observed within a given class of MHC products. The use of H-2Kb-specific mAb in blocking studies as an attempt to define further the H-2Kb epitopes recognized by CTL clones indicated that: a) TNBS treatment may affect the antigenicity of the H-2Kb molecule as assessed by some mAb; and b) that the T cell clone-target cell interaction may or may not be inhibited by a given mAb, depending on structural variations of the H-2Kb molecule (use of H-2Kbm mutants) that do not affect the interaction itself. These results indicate that this type of analysis does not permit correlation of serologic- and T cell-defined epitopes.     

Activation of Lyt-1+ and Lyt-2+ T cell cloned lines: stimulation of proliferation, lymphokine production, and self-destruction

Antigen-induced activation of a chicken gamma-globulin (CGG)-specific Lyt-1+ T cell clone measured both as a function of proliferation and immune interferon (IFN-gamma) production is restricted by a class II determinant of the major histocompatibility complex (MHC) mapped to the I-A subregion, as determined by studies with both recombinant inbred lines and monoclonal antibodies. Activation of Lyt-2+ picryl chloride (PC1)-specific cloned T cell lines by trinitrophenyl (TNP)-coupled spleen cells results in proliferation and the production of at least two lymphokines: lymphotoxin (LT) and IFN-gamma. This antigen-specific activation is restricted to a class I determinant of the MHC complex encoded in the K region. Thus, the common intracellular pathway leading to production of IFN-gamma by Lyt-1+ and Lyt-2+ T cells is mediated and restricted through different surface recognition units. The LT that is produced by antigen-specific activation of T cells not only kills fibroblasts, but it inhibits interleukin 2 (IL 2)-maintained T cells as well. Activation of T cells by concanavalin A (Con A) results in suicidal inhibition of proliferation and cell death by those clones that make LT, but not by those that produce only IFN-gamma under such induction conditions. These results indicate that it is neither Con A nor IFN-gamma that kills T cells, but LT. These results strongly suggest a self-regulatory role of LT in limiting continuing unrestricted T cell response to antigen activation.     

Analysis of the negative allogeneic effect using B cells and helper T cell lines as an indicator system: B cells identified as target cells for suppression

The target cells for H-2b T lymphocytes mediating a negative allogeneic effect in vitro were analyzed by using carrier-specific helper T cell lines of H-2b, H-2d, or F1 origin and hapten-primed T-depleted spleen cells also expressing one or both of these haplotypes. The helper T cell lines were shown to be carrier specific and H-2b or H-2d restricted. Most importantly, the lines derived from H-2b homozygous mice were devoid of alloreactivity against H-2d and vice versa. Titration of naive H-2b T lymphocytes to the indicator cultures resulted in suppression of the secondary anti-DNP response of the indicator cells whenever the B cells expressed H-2d antigens. The lack of suppression observed in mixtures in which only the helper T cell lines expressed H-2d antigens was not reversed by the increased addition of naive H-2bxd cells, indicating that an insufficient amount of H-2d antigens present on the low number of helper T cells used did not account for this finding. Moreover, the polyclonal plaque-forming cell responses of F1 spleen cells to LPS were also suppressed by naive parental T cells. From these findings it is concluded that the suppressor T cells directly recognize and inhibit allogeneic B cells without the involvement of helper T cells. In addition, it was shown that the suppression of secondary anti-hapten responses by naive allogeneic T cells is blocked by monoclonal anti-Lyt-2 antibody added at the onset of culture. Addition late in culture had no effect, pointing to a functional role of the Lyt-2-bearing structure at an early stage of the suppressive events resulting in the negative allogeneic effect.     

H-2K-restricted granuloma formation by Ly-2+ T cells in antibacterial protection to facultative intracellular bacteria

Cellular, genetic, and antigenic requirements for granuloma formation in murine listeriosis were determined by using adoptive transfer of granuloma formation. Granuloma formation was restricted by a class I MHC antigen (H-2K) and critically depended on a Ly-2+ (Ly-1+2+) T cell. Expression of granuloma formation required living bacteria; heat-killed bacteria was not sufficient. H-2K-restricted transfer of granuloma formation was associated with a high degree of protection. Markedly less protection, presumably due to macrophage activation by T cells, was found under conditions of H-2 I-A homology. It is concluded that two T cell populations are involved in protection against L. monocytogenes: protection associated with granuloma formation depends on Ly-2+ (Ly-1+2+) T cells, is restricted by H-2K, and requires products of living bacteria to be expressed, whereas protection based on macrophage activation depends on H-2 I-A-restricted T helper cells.     

Functional heterogeneity of the Lyb-5- B cell subpopulation: mutant xid B cells and normal Lyb-5- B cells differ in their responsiveness to phenol-extracted lipopolysaccharide

In the present study, responses stimulated by phenol-extracted lipopolysaccharide (LPS(phenol)) and butanol-extracted LPS (LPS(butanol)) were used to assess the possibility that xid B cells might not be identical to the Lyb-5- B cells present in normal mice. It was found that xid B cells responded well only to LPS(butanol) whereas normal B cells responded well to both LPS(butanol) and LPS(phenol). Thus, LPS(butanol) appeared to be a TI-1 antigen and LPS(phenol) appeared to be a TI-2 antigen. In contrast to classical TI-2 responses, however, responses stimulated by LPS(phenol) did not exhibit a stringent requirement for accessory cells. Furthermore, if LPS(phenol) were a classical TI-2 antigen, it should only activate Lyb-5+ B cells. To determine if the responsiveness of normal B cells to LPS(phenol) were due, at least in part, to the stimulation of normal Lyb-5- B cells, the responsiveness of normal neonatal B cells and normal adult B cells that had been pretreated with anti-Lyb-5.1 + C was assessed. It was found that both normal neonatal B cells and normal adult Lyb-5- B cells did respond well to LPS(phenol). Thus, even though LPS(phenol) does not stimulate xid B cells, these data demonstrate that LPS(phenol) is different from other TI-2 antigens. More importantly, these data also demonstrate that xid B cells and normal Lyb-5- B cells are not identical. It is hypothesized that the normal Lyb-5- B cell subpopulation is heterogeneous, consisting of an Lyb-5(1)- and an Lyb-5(2)-B cell subset with the xid mutation blocking the differentiation of Lyb-5(1)-B cells into Lyb-5(2)-B cells.     

Activation of B cells by autoreactive T cells: cloned autoreactive T cells activate B cells by two distinct pathways

Although the existence of autoreactive T cells has been widely reported, the functional capacities of these populations have been less well defined. Studies were therefore carried out to characterize the relationship of autoreactive T cells to antigen-specific major histocompatibility complex (MHC)-restricted T cells in their ability to act as helper cells for the induction of immunoglobulin synthesis by B cells. A number of autoreactive T cell lines and clones were isolated from antigen-primed spleen and lymph node cell populations. Autoreactive T cells were found to proliferate in response to direct recognition of syngeneic I-A or I-E subregion-encoded antigens in the absence of any apparent foreign antigen. It was shown that cloned autoreactive T cells were capable of activating B cell responses through two distinct pathways. After appropriate stimulation by syngeneic cells, autoreactive T cells polyclonally activated primed or unprimed B cells to synthesize IgM antibodies. These activated T cells functioned in these responses through an MHC-unrestricted pathway in which polyclonal responses were induced in both syngeneic and allogeneic B cells. These cloned autoreactive T cells were also able to activate IgG responses by primed B cells through a different activation pathway. In contrast to the polyclonal activation of IgM responses, the induction of IgG antibodies by the same cloned T cells required primed B cells and stimulation with the priming antigen. The activation of B cells to produce IgG was strongly MHC restricted and required the direct recognition by the autoreactive T cells of self MHC determinants expressed on the B cell surface, with no bystander activation of allogeneic B cells. These results indicate that cloned autoreactive T cells resemble antigen-specific MHC-restricted T cells in their ability to function as T helper cells through distinct MHC-restricted and MHC-unrestricted pathways.     

H-2-restricted cytolysis of L cells doubly transformed with a cloned H-2Kb gene and cloned retroviral DNA

We report the construction of target cells by the double transformation of mouse L cells with a cloned H-2Kb gene and molecular clones of Akv or Gross murine leukemia virus (MuLV) or the cloned gag gene of Akv MuLV. Cytolytic T lymphocytes (CTL) generated in BALB.B mice specific for Gross MuLV (closely related to Akv MuLV) kill these doubly transformed cells. This is a direct indication that a CTL subpopulation recognizes H-2Kb antigen in association with a viral antigen encoded by the gag gene of Gross MuLV.     

Induction of the H-2 D antigen during B cell activation

Mitogenic activation causes increased expression of class I Ag of the MHC in mouse B cells. The increased expression was seen in flow cytometry analysis for both K and D in k as well as d haplotypes. A more detailed molecular analysis was carried out for H-2Dd. Increased expression (10- to 20-fold) of the H-2 Dd gene was detected at both protein and messenger RNA levels, and the time course for the accumulation of H-2 Dd protein on the cell surface parallels the increase in the steady-state messenger RNA levels. The increase in H-2 Dd expression in small B cells stimulated with LPS is detectable after 10 h of culture. The present data provide molecular and serologic evidence about alterations in the expression of the H-2 Dd Ag, previously identified as a B cell activation antigen B7.2. Our results indicate a new significance for the function and regulation of the MHC during immune responses, and suggest that the class I molecules may serve some role in the B cell activation process.     

Ia Restriction Specificity of KLH-Specific T Cells from Allogeneic Bone Marrow Chimeras Is Influenced by Histocompatibility at the H-2 and Minor Histocompatibility Loci

Ia restriction specificity involved in T cell proliferative responses to keyhole limpet hemocyanin (KLH) has been analyzed using a variety of allogeneic bone marrow chimeras. The chimeric mice were prepared by reconstituting irradiated AKR, SJL, B10.BR and B10.A(4R) mice with bone marrow cells from B10 mice. When such chimeric mice had first been primed with KLH in complete Freund's adjuvant (CFA), T cells from H-2 incompatible fully allogeneic chimeras showed significantly higher responses to KLH in the presence of antigen-presenting cells (APC) of donor strain (B10) than APC of recipient strain. However, in H-2 subregion compatible chimeras, [B10→B10.A(4R)], which were matched at the H-2D locus and at minor histocompatible loci, the T cells could mount vigorous responses to KLH with antigen-presenting cells (APC) of either donor or recipient type. The same results were obtained as well with chimeras that had been thymectomized after full reconstitution of lymphoid tissues by donor-derived cells. A considerable proportion of KLH-specific T cell hybridomas established from [B10→B10.A(4R)] chimeras exhibited both I-A^b and I-A^k restriction specificities. The present findings indicate that the bias to donor Ia type of antigen specific T cells is determined by donor-derived APC present in the extrathymic environment but that cross-reactivity to the recipient Ia is influenced to some degree by histocompatibility between donor and recipient mice, even though the histocompatible H-2D locus and minor histocompatibility loci seem not to be directly involved in the I-A restricted responses studied herein.     

Cloned allospecific human helper T cell lines induce an MHC-restricted proliferative response by resting B cells

To analyze helper T (Th) cell-induced B cell proliferation in man, we have cloned allospecific Th cells, grown them as long-term IL 2-dependent T cell lines (TCL), and analyzed their phenotypic and functional properties. The two TCL described in this report, A-7 and A-57, are both composed exclusively of T3+, T4+, T8- T cells blasts. In proliferative assays, with a panel of x-irradiated allogeneic stimulator cells, A-7 was found to proliferate in response to DR3-bearing cells, whereas A-57 responds to DR2-positive stimulators. Both TCL are capable of providing MHC-restricted polyclonal help for allogeneic B cells, as measured in the reverse hemolytic plaque assay. Of greater interest, x-irradiated A-7 and A-57 cells are capable of inducing a proliferative response by allogeneic B cells that is absolutely MHC restricted at the inductive (Th-APC) level. Thus, x-irradiated A-7 cells only trigger proliferation by DR3+ B cells, whereas A-57 cells selectively activate DR2+ B cells. In contrast, after antigen-specific activation, x-irradiated A-7 and A-57 cells can recruit a significant proliferative response by allogeneic B cells bearing "irrelevant" DR antigens. The possibility that Th-induced B cell proliferation may be restricted at the effector (Th-B cell) level was addressed by fractionating B cell populations into "activated" and "resting" subsets by discontinuous Percoll density gradient centrifugation and further purification by employing a monoclonal antibody directed against an antigen expressed on activated B cells (4F2). These studies demonstrate that activated B cells are readily and nonspecifically recruited to proliferate by activated Th cells, whereas optimal proliferative responses by resting B cells require MHC restricted Th-B cell interaction.     

A role for Lyb-2 in B cell activation mediated by a B cell stimulatory factor

The Lyb-2 system of the mouse is involved in regulation of a proliferative step in the differentiation of B cells responding to T-dependent antigen. The present study concerns the role of Lyb-2 in an early phase of B cell activation with respect to B cell receptor functions for activation factors. It is shown that interaction of monoclonal anti (alpha)-Lyb-2 antibody with Lyb-2 on the B cell surface induces B cell proliferation by synergistic action with B cell growth factor II-containing factor or interleukin 1. In contrast, alpha-Lyb-2 antibody could not synergize with the Con A-induced culture supernatant of T cell hybridoma FS6-14.13 (FS6) containing B cell stimulatory factor-1 (BSF-1; formerly called BCGF I), and the effect of combining the two was only additive on B cell proliferation. Absorption studies showed that BSF-1 in FS6 could be absorbed by unstimulated B cells, about 95% of which were at Go phase of the cell cycle, but not by thymocytes, and more importantly that alpha-Lyb-2 antibody blocked the absorption in an Lyb-2-specific manner, possibly by competing with BSF-1. It is thus likely that alpha-Lyb-2 antibody may interact with a BSF-1 receptor on B cells or a molecule closely associated with it. Interestingly, alpha-Lyb-2 antibody mimicked the action of BSF-1 in a costimulator assay with affinity-purified goat alpha-mouse IgM antibody, but could not replace all the activities ascribed to BSF-1. Possible mechanisms involved are discussed.     

Human lymphocyte differentiation antigens HB-10 and HB-11. II. Differential production of B cell growth and differentiation factors by distinct helper T cell subpopulations

Two monoclonal antibodies (HB-10 and HB-11), which react with human T, B, and NK cells, identify approximately 50% of the Leu-3+ T helper (TH) cells in adult blood. In the present studies, the functional capabilities of the HB-11+ and HB-11-TH cell subpopulations were examined after purification by fluorescence-activated cell sorting. Both subpopulations proliferated in response to PHA, Con A, PWM, and OKT-3 antibodies. The HB-11+ TH cells gave a minimal proliferative response to soluble tetanus toxoid antigen, whereas HB-11-TH cells responded well. After mitogen activation, both HB-11+ and HB-11-TH cells and to produce soluble factors which induce large B cells to proliferate. However, PWM-stimulated HB-11+TH cells were incapable of inducing B cells to differentiate into antibody-secreting plasma cells, whereas HB-11-TH cells were efficient in this regard. The results suggest that the HB-11 antigen is expressed on a subpopulation of virgin TH cells that can produce B cell growth factors but are deficient in the ability to produce B cell differentiation factors.     

Contribution of Lyb 5+ and Lyb 5- B cells to the primary and secondary phosphocholine-specific antibody response

Due to a mutation on their X-chromosome, CBA/N mice lack the Lyb-5+ subset of B cells. The loss of this B cell subset results in a profound alteration in the immune response of these mice to the hapten phosphocholine (PC). Thus, when these mice are immunized with high doses of PC-KLH (200 micrograms) in CFA, they: 1) fail to produce IgM anti-PC antibodies; 2) produce little or no anti-PC antibody bearing the normally predominant T15-idiotype; and 3) produce IgG anti-PC antibodies only late in the primary response. In order to more fully delineate this defect in responsiveness to PC, the splenic focus assay was used to analyze Lyb-5- B cell precursors from both normal and immune defective mice. Lyb-5- cells were obtained from normal (CBA/N x DBA/2)F1 (CD) female spleens by treatment with anti-Lyb-5 serum and complement. These normal Lyb-5- cells and Lyb-5- cells from immune defective CD male mice were stimulated in vitro with either PC-Hy or TNP-Hy in the presence of Hy-primed T helper cells. The results demonstrate that primary Lyb-5- PC-specific B cells fail to respond in the splenic focus assay, while secondary Lyb-5- PC-specific precursors respond normally, and that both primary and secondary Lyb-5- TNP-specific precursors respond in the splenic focus assay. These data suggest that Lyb-5- PC-specific precursors must differentiate into memory cells before they can be activated to secrete antibody, and they also indicate that the Lyb-5- B cell subset may be composed of two subsets with different activation requirements.     

Characterization of murine T cell activation signals produced by B lymphoma cells

The activation requirements of alloreactive and antigen reactive murine T cells were examined by stimulating class II restricted T cell clones with monoclonal B lymphoma cells. One B lymphoma cell line (T27A) was found to stimulate IL 2 release from some alloreactive T cell clones without stimulating any significant T cell proliferation response. The same B lymphoma cells are capable of stimulating IL 2 release and proliferative responses from other T cell clones. Evidence is presented suggesting that B lymphoma cell stimulation of these T cell clones is largely IL 1 independent and that at least some T cell clones may require activation signals other than Ia, antigen, and IL 1. The addition of exogenous, purified IL 1 to the T cell activation assays was found to have a wide range of stimulatory effects on the proliferative responses of different T cell clones. The absence of comparable IL 1-induced stimulation of IL 2 secretion suggests that IL 1 primarily enhances antigen specific T cell proliferation through mechanisms other than acting as a co-stimulant for IL 2 release.