Requirement for noncognate interaction with T cells for the activation of B cell immunoglobulin secretion by IL-2

The mechanism whereby noncognate contact with activated IL-2-producing Type 1 helper T cells (TH1) induces B cell activation was examined. Small resting B cells from C57B1/6 mice were cultured, in the absence of any ligand for surface Ig, with irradiated cells of the hapten-specific, CBA-derived, F23.1+ TH1 clone E9.D4 in F23.1 (anti-T cell receptor V-beta 8)-coated microwells. This induced polyclonal B cell activation to enter cell cycle (thymidine incorporation) at 2 days and to secrete immunoglobulin at 5 days. An anti-IL-2 mAb (S4B6) inhibited antibody production completely. Anti-IL-2 did not inhibit either LPS-induced B cell responses, or T cell activation (measured as IL-3 secretion). Anti-IL-2 receptor (anti-Tac) mAbs also inhibited T-dependent B cell responses, without affecting LPS responses. An anti-IFN-gamma mAb partially inhibited Ig secretion, without affecting entry into cycle. LPS responses or T cell activation. Other antibodies (anti-IL-3, IL-4, IL-5, Thy-1.2, CD5) were not inhibitory. After 2 days of culture with F23.1-activated T cells, B cells appeared to have become responsive to IL-2, in that they could be driven to immunoglobulin production by the addition of IL-2. Flow cytometry showed no expression by these B cells of 55-kDa (Tac) IL-2 receptors. Also, rigorous removal of T cells from 2-day cocultures prevented the response to IL-2, and readdition of T cells restored it. Because the reconstituted responses were inhibited both by anti-IL-2 and by anti-Tac, IL-2 must have acted indirectly, via the T cells that were present in these cultures. Continued contact with T cells was therefore necessary for the progression of B cells to antibody secretion.     

Immunoglobulin-dependent helper T cells: studies in the MOPC-315 system suggest a novel surface antigen phenotype

We have previously provided evidence that the SRBC-immune helper T (TH) cells which enhance MOPC-315 plasmacytoma cell secretory differentiation in vivo (THd cells) differ in specificity, accessory cell requirements, and Qa-1 expression from the SRBC-immune TH cells which enhance MOPC-315 cell growth in vivo (THg cells). Indeed, like other immunoglobulin-dependent TH cells, THd cells in the 315 system do not develop in anti-IgM-treated, B cell-deficient mice, whereas THg cell development is unaffected. In this report, we provide evidence for other differences in the expression of surface antigens by these two TH cell populations. We find that, like most Lyt-1+, 2- T cells, the THg cells can be eliminated by monoclonal anti-L3T4 antibody and complement treatment, whereas such treatment had no effect on adoptive transfer of SRBC-immune THd cell activity. Similarly, THg cell activity was eliminated from SRBC-immune T cells by treatment with monoclonal anti-T cell receptor beta-chain allotope antibody plus anti-rat IgG and complement, whereas THd cell activity remained intact. Both helper cell activities were deleted by either anti-Lyt-1.2 or anti-Thy-1.2 antibody and complement treatment. Interestingly, the THd cell activity was abrogated by treating SRBC-immune T cells with monoclonal anti-B220 or monoclonal anti-p50 antibodies (RA3-3A1/6.1 and RA3-2C2/1, respectively) and complement, whereas THg cell activity was unaffected. Additional controls indicated that the THd effects did not arise by virtue of a two-cell interaction between a Thy-1+, B220- cell and a Thy-1-, B220+ cell, and it is therefore proposed that the THd effect arises from a single population of cells that exhibit a unique phenotype (Thy-1+, Ly-1+, 2-, L3T4-, B220+). The proposal is further supported by studies conducted with a T cell clone which promotes MOPC-315 cell secretory differentiation in vitro and which exhibits this surface antigen phenotype. The serologic differences between these two TH cell populations stress even further the likelihood that B cell growth and differentiation enhancement are mediated by distinct T cell subsets in this system, and raise the possibility that immunoglobulin-dependent TH cells in other systems will routinely exhibit a unique surface antigen profile. These data also imply that immunoglobulin-dependent TH cells (such as the THd cells) may not express antigen receptors that are identical to those expressed by MHC-restricted helper cells (such as our THg cells).     

Antigen-specific sIalo B cells do not secrete IgG2a in response to TH1 cells and antigen: responsiveness can be restored by IL-4

The ability of Th cells, type 1 (TH1), to activate and induce differentiation of B cells into antibody-secreting cells is controversial because 1) some clones of TH1 cells provide help while others do not, and 2) by using the same TH1 clone, different laboratories disagree on whether they provide help to B cells. One possible explanation for the latter is the variability in the activation status of the B cells used in different laboratories. In the present studies, we have used Ag-specific B cells from athymic (nu/nu) mice, or sterilely housed nu/+ mice to study the TH1-mediated activation of B cells that had received little or no prior help from T cells and/or antigen in vivo. These B cells express low levels of surface Ia (sIa) Ag, and fail to secrete IgG2a in response to TH1 cells plus Ag; in contrast, responses to TH2 cells plus Ag are normal. To explore this observation further, we prepared "surface(s) Ia1o" B cells from conventionally housed BALB/c mice by sorting spleen cells on the fluorescence-activated cell sorter. This sIalo population also failed to produce IgG2a in response to TH1 cells plus Ag. In contrast, the sIahi, (presumably more mature) B cells, responded to both the TH1 and TH2 cells. The addition of LPS, TH2 cells or the lymphokine, IL-4, to cultures of sIalo B cells from normal or nu/nu mice (plus Ag and TH1 cells), restored IgG2a responses to control levels. Low sIa levels were not the sole cause of nonresponsiveness of the nu/nu B cells because a 24-h pulse with IL-4 restored sIa to control levels without restoring IgG2a production after activation with TH1 cells plus Ag. These data support the conclusion that sIalo B cells are immature and require an activation/maturation signal from IL-4 in vivo in order to respond to TH1 cells and Ag in vitro.     

Characterization of a T4+/Leu-8+ T cell clone that directly helps B cell Ig production by secreting B cell differentiation factor

A human T4+/Leu-8+ T cell clone (YA2) was established by phytohemagglutinin activation and interleukin 2 (IL 2) propagation. Functional characterization of this clone demonstrated that it provided potent help towards Ig production by pokeweed mitogen-stimulated B cells in the presence of small numbers of autologous T cells or by Staphylococcus aureus Cowan I (SAC)-activated B cells in the presence of B cell growth factor (BCGF). YA2 provided no help to resting B cells and minimal help to either unactivated B cells cultured with BCGF or SAC-activated B cells. Supernatant generated from clone YA2 by IL 2 stimulation had significant B cell differentiation activity but no BCGF or IL 2 activity. Thus, YA2 is a T4+/Leu-8+ potent direct helper only to B cells that are activated and proliferating due to its selective secretion of a differentiation factor, and not an activation and growth factor. The availability of phenotypically defined cloned populations of T cells with restricted functional helper activity related to the secretion of selected B cell tropic factors should prove useful in the dissection of the role of individual T cell subsets in the regulation of the human B cell cycle.     

In vitro induction and expression of interleukin 2 receptor in a clonal T helper cell differentiation model

Induction and expression of interleukin 2 (IL 2) receptor have been studied using a poly( Glu60 Ala30 Tyr10 ) (GAT)-specific T cell clone of mouse origin. This clone (52-3) has been characterized and it exhibits functional properties of T helper (TH) cells: it leads to a specific anti-DNP response in the presence of DNP-GAT and DNP-primed B cells and it secretes biological activities which can induce polyclonal B cell proliferation and IgM secretion. In vitro this clone mimics the activation stages of normal T lymphocytes and can be obtained under two states of differentiation. depending on the antigen-specific signal provided by antigen-presenting cells (APC). The expression of IL 2 receptor by this clone has been studied by (i) its response to IL 2, (ii) its capacity to absorb IL 2 bioactivity, and (iii) its reactivity with monoclonal antibody 7D4 specific for mouse IL 2 receptor. All the results indicate that the unstimulated state does not express the IL 2 receptor while the activated state does. Clone 52-3 has been compared with clone 14-1.6 that derives from a TH cell line and expresses the IL 2 receptor constitutively. 52-3 offers a good experimental model for studying in vitro, in a clonal TH cell population, the detailed mechanism of IL 2 receptor induction.     

Gangliosides: differentiation markers for murine T helper lymphocyte subpopulations TH1 and TH2.

On the basis of the pattern of lymphokines they secrete, murine T helper clones can be divided into two subsets, TH1 and TH2. This concept of two different T helper effector cells helps to explain the diversity of immune reactions occurring in different parts of the body. The in vivo localization of T helper subtypes is of great interest, but up to now no biochemical or surface markers were available to distinguish between them. We analyzed the glycolipids from altogether 12 murine TH1 and TH2 cell lines or clones. A comparison of the gangliosides by thin-layer chromatography showed differences between the TH1 and TH2 cells. Binding studies with specific antibodies to asialo backbone structures after degradation by neuraminidases showed that the main gangliosides from these lymphocytes shared a common GgOse4 backbone and thus differed only in their degree or position of sialylation. Two disialogangliosides appeared to be characteristic. They were isolated from the D10.G4.1 TH2 cell clone and identified by fast atom bombardment mass spectrometry as IVNeuAc,IINeuAc-GgOse4Cer (GD1a) and IVNeuAc,IIINeuAc-GgOse4Cer (GD1 alpha), respectively. GD1a was characteristically only detected in TH2 cells, whereas GD1 alpha was preferably, but not exclusively, expressed by TH1 lymphocytes. Although GD1a was also found in the lung, heart, kidney, and spleen, its expression within the murine immune cells under investigation was unique to TH2 lymphocytes. Scarcely any GD1a was found in thymocytes, B cells, or CD8 positive (cytolytic) T cells, but significant expression was seen in CD4 positive (helper) T cells which include the TH2 subpopulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of iron in T cell activation: TH1 clones differ from TH2 clones in their sensitivity to inhibition of DNA synthesis caused by IgG Mabs against the transferrin receptor and the iron chelator deferoxamine.

TH1 and TH2 helper T cell clones have been studied with respect to their sensitivity to inhibition of DNA synthesis by an IgG anti-transferrin receptor antibody (ATRA), the iron chelator deferoxamine, and the combination of the two reagents. TH1 clones are very sensitive to ATRA-mediated inhibition of DNA synthesis while TH2 clones are very resistant, but both TH1 and TH2 clones show significant down-modulation of surface transferrin receptors after ATRA exposure. TH2 clones exhibit larger chelatable iron storage pools than TH1 clones, however, and even partial chelation of TH2 cell storage iron does not fully convert a TH2 clone to the ATRA sensitivity pattern of a TH1 clone. It is therefore proposed that the greater resistance of TH2 clones to ATRA mediated inhibition derives from the combined effects of larger and less labile iron storage pools. These studies provide novel evidence indicating that nonuniform iron metabolism can exist within the T cell compartment and thus raise questions as to why such differences exist and how they can be integrated into models of the T cell activation process. These studies also suggest that the cell-mediated immune response in vivo, which is known to be sensitive to iron deficiency, may be evoked by effector cells which resemble TH1 clones insofar as iron metabolism is concerned.     

Antigen-specific, MHC-restricted B cell activation by cell-free Th2 cell products. Synergy between antigen-specific helper factors and IL-4

Ag-specific and MHC-restricted Th clones of different Ag specificities and MHC haplotypes were tested for their ability to produce soluble factors capable of providing the signals required for B cell activation and IgG antibody production. Each of five Th clones tested generated significant helper activity in supernatants derived from coculture of the T cell clone with specific Ag and syngeneic APC. The same helper activity was detected in supernatants of clones stimulated with immobilized anti-CD3 antibody in the absence of Ag or APC. The secreted helper activity resembled the activity of the intact Th cells in that it was Ag-specific, carrier-hapten-linked and MHC-restricted. These T cell products functioned to activate only those B cells expressing MHC products which corresponded to the specificity of each Th clone. Thus, the specificity of the cell-free T cell product mimicked precisely that expressed by the intact Th cell and presumably mediated by the cell surface TcR. In addition to the apparent presence of specific helper factor in Th clone supernatants, a role for nonspecific lymphokines was also identified in these preparations. Although recombinant or purified IL-4 alone was not sufficient to stimulate hapten-primed B cells to secrete hapten-specific IgG antibodies, mAb specific for IL-4 blocked the induction of antibody secretion by Th cell supernatant. These results indicate that stimulation of B cells to produce hapten-specific IgG antibody requires at least two distinct signals: an Ag-specific T cell signal which is restricted by MHC products expressed on the B cells, and a nonspecific signal mediated at least in part by the lymphokine IL-4.     

Two independent pathways of helper activity provided by a single T cell clone

Data presented in this paper demonstrate the existence of two separate pathways by which a single T cell clone can induce B cell differentiation. With the use of high doses of antigen, a T cell clone can induce a primary antibody response in unprimed B cells. With the use of low doses of antigen, the same T cell clone can induce an immunoglobulin (Ig)G response in primed B cells. The primary response is accompanied by T cell proliferation and lymphokine production (interleukin 2, B cell growth factor, B cell differentiation factor for immunoglobulin M, and B cell differentiation factor for immunoglobulin G). The secondary response does not require proliferation and occurs independently of detectable lymphokine production. Variants of the wild type T cell helper clone have been isolated. One variant can provide help to unprimed B cells when high doses of antigen are used. This variant cannot provide help to primed B cells when low doses of antigen are used, nor can it provide help to CBA/N "xid" B cells at any antigen concentration tested. Additional variants have been isolated that proliferate on antigen-pulsed-presenting cells, but fail to secrete detectable lymphokines and do not induce B cell differentiation. These results suggest that a single T cell helper clone has multiple functional activities that can be independently expressed.     

Idiotypic networks incorporating T-B cell co-operation. The conditions for percolation

Previous work was concerned with symmetric immune networks of idiotypic interactions amongst B cell clones. The behaviour of these networks was contrary to expectations. This was caused by an extensive percolation of idiotypic signals. Idiotypic activation was thus expected to affect almost all (greater than 10(7] B cell clones. We here analyse whether the incorporation of helper T cells (Th) into these B cell models could cause a reduction in the percolation. Empirical work on idiotypic interactions between Th and B cells however, would suggest that two different idiotypic Th models should be developed: (1) a Th which recognises native B cell idiotypes, i.e. a non-MHC-restricted "ThId" model, and (2) a "classical" MHC-restricted helper T cell model. In the ThId model, the Th-B cell interaction is symmetric. A 2-D model of a Th and a B cell clone that interact idiotypically with each other accounts for various equilibria (i.e. one virgin and two immune states). Introduction of antigen does indeed lead to a state switch from the virgin to the immune state; such a system is thus able to "remember" its exposure to antigen. Idiotypic signals do however, percolate in ThId models via these "B-Th-B-Th" pathways: proliferating Th and B cell clones that interact idiotypically, will always activate each other reciprocally. In the MHC-restricted Th model, Th-B interactions are asymmetric. Because the B cell idiotypes are processed and subsequently presented by MHC molecules, the Th receptor and the native B cell receptor are not expected to be complementary. Thus the Th and the B cells are unable to activate each other reciprocally, and a 2-D Th-B cell model cannot account for idiotypic memory. In contrast to the ThId model, idiotypic activation cannot percolate via "B-Th-B-Th" interactions. Due to the assymmetry idiotypic activation stops at the first Th level. A Th clone cannot activate a subsequent B cell clone: if the B cells recognise the Th cells, they see idiotype but get no help; if the Th cells see the B cells, the B cells are helped but see no idiotype. The percolation along "B-B-B" pathways in these two models is next analysed. Two B cells clones, each helped by one Th clone, are connected by a symmetric idiotypic interaction. It turns out that in both models the second (i.e. anti-idiotypic) B cells (B2) never proliferate.(ABSTRACT TRUNCATED AT 400 WORDS)     

Polyclonal activation of xid B cells by auto-Ia-reactive T cell clones

The mechanism of T cell-dependent activation of xid B cells into Ig-producing cells was studied by employing H-2-restricted, antigen-specific T cell clones. Helper factors (B cell stimulatory factors, BSF) released from KLH-specific T cell lines could induce polyclonal Ig production in B cells from (CBA/N X BALB/c)F1 (NBF1) female mice but not from CBA/N or NBF1 male mice. Direct addition of helper T cell lines induced Ig production in xid B cells from CBA/N or NBF1 male mice. A T cell clone, MK6, which was derived from NBF1 male mice and specific against Iad determinant, could activate NBF1 male but not CBA/N B cells. Another clone, CK4, derived from CBA/N mice and having specificity against KLH plus I-Ak determinant could activate both CBA/N and NBF1 male B cells into IgM- and IgG-producing cells in the absence of KLH, and monoclonal anti-I-Ak antibody specifically blocked such activation. These results suggest that xid B cells are able to be activated by the signal provided by the recognition of Ia molecules on B cells by auto-Ia-reactive T cells. Xid B cells from CBA/N mice that had been co-cultured with a T cell line specific against I-Ak determinant for 24 hr became reactive to BSF and capable of differentiating into Ig-producing cells in the presence of BSF. The results showed that even xid B cells could be responsive to BSF if they were in a certain activation stage.     

A polyclonal assay for T helper function involving T-B cell contact mediated by L3T4 molecules

In the presence of pokeweed mitogen (PWM), T helper (TH) cell clones can induce differentiation of a very high proportion of normal B lymphocytes into plasmocytes. This property can be used to test TH cell function regardless of clonal specificity. We have investigated the role of L3T4 surface antigen in this new assay. Only TH cell clones expressing the L3T4 antigen have effector activity in this PWM-dependent helper assay; L3T4- TH cell variants are inactive. The involvement of L3T4 antigen is further shown by the ability of anti-L3T4 monoclonal antibody to inhibit the PWM-dependent polyclonal B cell differentiation induced by L3T4+ TH cell clones. This inhibition is not the consequence of arrested TH cell activation, nor of a lack of appropriate B cell stimulation by TH cell lymphokines. We show that PWM focuses TH cells on the B cell hybridoma LB15-13, and that anti-L3T4 mAb prevents the T-B cell clustering mediated by PWM. Thus, by a mechanism comparable with the one described for concanavalin A in the cytotoxicity assay, PWM acts by bridging TH cells and B cells; the T cell surface antigen L3T4 is involved in this process.     

Two types of murine helper T cell clone. II. Delayed-type hypersensitivity is mediated by TH1 clones

We have previously shown that at least two types of Lyt-1+, Lyt-2-, L3T4+ helper T cell clones can be distinguished in vitro by different patterns of lymphokine secretion and by different forms of B cell help. Evidence is presented here to show that one type of helper T cell clone (TH1) causes delayed-type hypersensitivity (DTH) when injected with the appropriate antigen into the footpads of naive mice. The antigen-specific, major histocompatability complex (MHC)-restricted footpad swelling reaction peaked at approximately 24 hr. Footpad swelling was induced by all TH1 clones tested so far, including clones specific for soluble, particulate, or allogeneic antigens. In contrast, local transfer of TH2 cells and antigen did not produce a DTH reaction, even when supplemented with syngeneic spleen accessory cells. Similarly, local transfer of an alloreactive cytotoxic T lymphocyte clone into appropriate recipients did not produce DTH. The requirements for the DTH reaction induced by TH1 cells were investigated further by using TH1 clones with dual specificity for both foreign antigens and M1s antigens. Although these clones responded in vitro to either antigen + syngeneic presenting cells, or M1s disparate spleen cells, they responded in vivo only to antigen + MHC and did not cause footpad swelling in an M1s-disparate mouse in the absence of antigen. Moreover, in vitro preactivation of TH1 or TH2 cells with the lectin concanavalin A was insufficient to induce DTH reactions upon subsequent injection into footpads. From these results, we conclude that the lack of DTH given by TH2 clones in vivo could be due to the inability of the TH2 cells to produce the correct mediators of DTH, or to a lack of stimulation of TH2 clones in the footpad environment.     

Analysis of a TH1----TH2 helper cell circuit

In the present study, the T15 idiotype-recognizing T helper cell circuit was dissected with respect to its homeostasis, interactive specificity, stability over time, and effects on B cell expression. Analysis of the TH1 cells by adoptive transfer experiments indicates their short-lived state of activity, during which TH2 cells are stimulated. TH1 cell activity was also directly monitored by the use of TNP-anti-T15 hybridoma antigens. It was found that TH1 cells are detected 1 wk after priming with PC-Hy, whereas TH2 cells become activated after 4 wk of priming. Comparative analysis of TH1 cells by using two different TNP-anti-T15 hybridoma antigens indicates a TH1 specificity for a shared idiotope. The stability over time of the TH1----TH2 circuit was demonstrated by comparing TH2 frequencies in young and old mice. Finally, we addressed the question of the function of the idiotype-recognizing T helper cells and showed that stimulation of T15-idiotype-specific TH2 cells can be correlated with a significant increase in the percentage of T15 idiotype in an anti-PC response. Collectively, these data describe an idiotype-specific T helper circuit as part of the network homeostasis of the immune system.     

Induction of IL-2 receptor expression and proliferation of T cell clones by a novel cytokine(s).

We found a unique T cell IL-2 receptor (IL-2R)3-inducing activity in the supernatant (SN) of the TH1 clone stimulated with antigen on spleen cells as antigen-presenting cells (APC). We have tentatively named this activity the IL-2R-inducing factor (IL-2RIF) and have characterized the activity. The SN induced IL-2R and proliferation of TH1 clones stimulated with B cell APC, which could not induce IL-2R in the absence of the SN. Other known cytokines were examined for a IL-2RIF activity; however, none of cytokines examined exerted a similar activity. Moreover, the neutralizing antibodies against the known cytokines tested did not block the IL-2RIF activity in the SN. When TH1 clones were stimulated with immobilized anti-CD3 or with fixed B cell APC in the presence of partially purified IL-2RIF, these clones expressed IL-2R and showed IL-2-dependent proliferation, whereas they induced neither IL-2R expression nor proliferation in the absence of IL-2RIF activity. These observations suggest that IL-2RIF activity is mediated by a novel cytokine(s) and the cytokine plays an important role as a second signal in the activation of the TH1 clone.     

Functional diversity of T lymphocytes due to secretion of different cytokine patterns.

Different helper T cell subsets secrete different patterns of cytokines when stimulated by antigen. The TH1 and TH2 subsets differ in the secretion of at least eight cytokines, and three or more other cytokine secretion patterns also exist among both mouse and human T cell clones. Several properties of strong immune responses suggest that at least the TH1 and TH2 phenotypes can be present in vivo. As cytokines are major determinants of the functions of the T cells that produce them, these patterns lead to different properties of the T cell subsets. TH1 cells mediate several functions connected with cytotoxicity and local inflammatory reactions, and so these T cells are particularly effective at combating viruses and intracellular bacteria and parasites. TH2 cells are much more effective at stimulating B cells to produce antibody, and so should be more effective against free-living bacteria, and in inducing protective humoral immunity. Antibody and delayed inflammatory reactions are often mutually exclusive during immune responses, and this can be at least partially explained by cross-inhibition of TH1 and TH2 cells. A newly discovered cytokine, IL10, has been implicated as one of the cross-regulatory cytokines, as this TH2 product inhibits cytokine synthesis by TH1 cells.     

Recombinant T cell replacing factor (interleukin 5) acts with antigen to promote the growth and differentiation of single hapten-specific B lymphocytes

The role of murine recombinant T cell replacing factor (rTRF) (interleukin 5) in the early activation, proliferation, and antibody-forming cell (AFC) clone formation of single fluorescein (FLU)-specific B cells was examined in vitro. FLU-specific B cells were selected by their adherence to FLU-gelatin and then cultured in 10-microliters wells with or without rTRF in the presence or absence of the T-independent antigen FLU-polymerized flagellin (FLU-POL). rTRF acting alone was unable to induce early B cell activation as assessed by significant cell enlargement after 24 hr in culture. When acting in the presence of FLU-POL, however, a greater number of B cells were induced to enlarge than with FLU-POL alone. When FLU-specific B cells were cultured in the presence of FLU-POL, the addition of rTRF markedly increased the frequencies of both proliferating clones and AFC clones above that induced by FLU-POL alone. Furthermore, in the presence of FLU-POL, the activity of rTRF was comparable to that seen with the mixture of B cell growth and differentiation factors contained within the supernatant from concanavalin A-stimulated EL4 cells. However, rTRF exerted little activity when acting alone in contrast to the medium conditioned by concanavalin A-stimulated EL4 cells which showed some activity in the absence of FLU-POL. rTRF acting with FLU-POL also promoted AFC clone development among single B cells stimulated in the presence of 3T3 fibroblast filler cells. Thus rTRF can be added to the list of B cell active factors (including recombinant murine interleukin 1 and recombinant human interleukin 2) that act in the concomitant presence of antigen to induce both growth and differentiation among single hapten-specific murine splenic B cells. This stands in contrast to the activity seen with interleukin 4 (formerly termed B cell stimulatory factor 1) which acts to promote early activation and proliferation but not IgM secretion.     

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.     

Disparate functional properties of two interleukin 1-responsive Ly-1+2- T cell clones: distinction of T cell growth factor and T cell-replacing factor activities

We describe the properties of two Ly-1+2- T cell clones (Ly-1.14 and Ly-1.21), which are maintained in long-term culture in the absence of other cell types. The clones require media containing a source of interleukin 1 as well as interleukin 2. They retain physiologic responses to interleukin 1, which is required for optimal production of T cell lymphokines by these clones in response to concanavalin A (Con A). The two Ly-1+2- T cell clones differ in their production of lymphokines after stimulation by Con A. The supernatant of clone Ly-1.21 promotes the proliferation of T cells maintained in long-term culture, induces antibody synthesis in cultures of B cells and antigen, and induces the differentiation of cytolytic cells in cultures of thymocytes and antigen; these assays define the properties of T cell growth factor (TCGF), T cell-replacing factor for B cells (TRF-B), and T cell-replacing factor for cytolytic cells (TRF-C), respectively. In contrast, the supernatant of clone Ly-1.14 contains only TCGF activity and does not promote antibody synthesis by B cells or differentiation of cytolytic cells from thymocytes. The results indicates that TCGF and TRF activities reside on independent, although perhaps related, molecules.