- Email: [email protected]
Roles of the specific T-helper signal and the antigen signal in B-cell activation
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[28] MONROE, J. G. & CAMBIER,J. C., B-cell activation: B-cell plasma membrane depolarization and hyper-Ia antigen expression induced by receptor immunoglobulin cross linking are coupled. J. exp. Med., 1983, 158, 15891599. [29] RINGDEN, 0. • RYNNEL-DAGo(i,B:, Activation of human B and T lymphocytes by protein A of Staphylococcus aureus. Europ. J. Immunol., 1978, 8, 47-52. [30] PRYJMA, J., MUNOZ, J., GALBRAITH,R. M., FUDENBERG, H. H. & VIRELLA, G., Induction and suppression of immunoglobulin synthesis in cultures of human lymphocytes: effects of pokeweed mitogen and Staphylococcus aureus Cowan I. J. Immunol., 1980, 124, 656-661. [31] SCHUURMAN,R. K. B., GELFAND, E. W. & DOSCH, H.-M., Polyclonal activation of human lymphocytes in vitro. - - I. Characterization of the lymphocyte response to a T-cell-independent B-cell mitogen. J. Immunol., 1980, 125, 820-826. [32] SAIKI, 0. & RALPH, P., Induction of human immunoglobulin secretion. - - I. Synergistic effect of B-cell mitogen Cowan I plus T cell mitogens of factors. J. Immunol., 1981, 127, 1044-1047. [33] FALKOFF, R. J. M., ZHU, LI PING ZJI ~2 FAUCI, A. S., Separate signals for human B-cell proliferation and differentiation in response to Staphylococcus aureus: evidence for a two-signal model of B-cell activation. J. Immunol., 1982, 129, 97-102. [34] YOSHIZAKI, K., NAKAGAWA, T., KAIEDA, T., MURAGUCHI, A., YAMAMURA, Y. & KISI-IIMOTO, T., Induction of proliferation and Ig production in human B leukemic cells by anti-immunoglobulins and T-cen factors. J. Immunol., 1982, 128, 1296-1301. [35] OKADA, M. et at., B-cell growth factors and B-cell differentiation factor from human T hybridomas. J. exp. Med., 1983, 157, 583-590. [36] MURAGUCHI,A. et at., Differential sensitivity of human B-cell subsets to activation signals delivered by anti-~ antibody and proliferation signals delivered by a monoclonal B-cell growth factor. J. exp. Med., 1983, 157, 530-546.
ROLES OF T H E SPECIFIC T - H E L P E R SIGNAL AND T H E A N T I G E N SIGNAL IN B-CELL ACTIVATION b y R. Zubler Swiss Institute for Experimental Cancer Research, 1066 Epalinges s/Lausanne (Switzerland) I. - - Introduction.
I t is now generally accepted t h a t during a humoral immune response, the resting B cells m u s t first receive appropriate activation signals before they can proliferate and differentiate into antibody-secreting cells in response to T-cellderived non-specific soluble growth and possibly differentiation factors [1]. However, the exact nature and role of the activation signals (as of the non-specific factors) is still the subject of controversies. The questions addressed in this s h o r t discussion paper are (1) whether B-cell activation requires an Ia/carrier-specific T-cell signal which cannot be mediated by stable interleukins and (2) whether the interaction of specific antigens (or anti-Ig antibodies) with the surface immunoglobulins of B cells generates an activation signal. 2. - - The specificilg o[ T helper cell/B cell interactions. The occurrence of so-called linked recognition of hapten and carrier determinants b y B cells and T helper cells (Th) [2, 3] in conjunction with H-2 restriction
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at the level of T/B cell interactions in vivo as well as in vitro [4, 5, 6], and the capacity of B cells to present antigens to T cells [7] are now well established. In vivo, a specific T/B cell interaction certainly is important for the optimal delivery of non-specific T-cell factors [8] to B cells. However, a requirement for a specific T/B cell interaction can be demonstrated in vitro in well defined culture systems even in the presence of an artificially high concentration of non-specific T-cell factors and, therefore, most likely has additional effects, i. e., provides an essential B-cell activation signal [1, 6, 9-13]. This will be further discussed in the context of recent observations from this laboratory summarized in (( Section 4 ,). 3. - - ElTect o/ B cell~antigen interaction.
Normally, B cells can be recognized by T cells only if the B cells have themselves already recognized some antigen. However, in experimental systems in which the specificity of Th is directed against B-cell membrane antigens rather than conventional antigens, the effect of B cell/antigen (hapten) interaction can be analysed independently of its role in the focusing of Th onto B cells. Using this type of system, some authors obtained high polyclonal B-cell responses in the apparent absence of antigen recognition by the B cells and thus concluded that a specific Th signal is by itself sufficient for B-cell activation [11]. In other studies [12], including those from my own laboratory [13], it was for the generation of optimal antigen-specific (or polyclonal) plaque-forming cell (PFC) responses in the presence of cloned H-Y-specific Th required t h a t the B cells themselves could see specific antigens (or react with anti-Ig antibodies). In addition, with regard to polyclonal B-cell activation systems in current use in different laboratories for the characterization of the non-specific factors acting on B cells, it seems t h a t anti-Ig antibodies alone or together with soluble factors can induce B-cell activation, i. e. in the absence of T cells [14, 15]. If this is true, polyclonal B-cell activation requires either Th alone or anti-Ig alone. In my own recent studies, this has been reinvestigated and the results will be briefly summarized. 4. - - Requirements/or the induction o/growth/actor responsiveness o / B cells [16].
Low numbers of purified B cells (108/200 ~1 or less) were placed into cultures containing different types of irradiated cloned T cells, i. e. subclones derived from H-Y-specific cloned Th which either (a) still provided a male-specific (or ConAmediated non-specific) B-cell activation signal but had lost the capacity to generate B-cell growth factor or (b~ had lost all detectable helper activities. This type of culture system was used to analyse the effects of Th, anti-Ig and/or T-cell factors, firstly because it can be assumed to contain few undefined T cells which m a y contaminate B-cell preparations and, secondly, because only low numbers of B cells can optimally proliferate in a polyelonal system without overgrowing the cultures. It was found that anti-Ig (polyvalent, affinity-purified rabbit anti-mouse Ig coupled to sepharose beads) was capable of and, in fact, was required for inducing growth factor responsiveness of B cells in cultures with ConA and T cells of type a, i. e. the addition of anti-Ig and T-cell supernatants (SN) led to potent thymidine incorporation. However, anti-Ig and T-cell SN did not lead to any response in cultures with Th of type b. In cultures with Th of type b, the addition of lipopolysaccharide (LPS), anti-Ig and T-cell SN together led to a high proliferative response. Thus, the study demonstrated that a ConA-mediated Th signal (which could not be replaced by soluble factors) and anti-Ig or (in cultures without competent Th) LPS and anti-Ig were required for optimal polyclonal B-cell activation. Using a B-cell-limiting dilution assay and measuring the generation of clones of protein-A PFC, it was found t h a t two activation signals provided by Th and anti-Ig (or by LPS and anti-Ig) had to act on the same B cells, i. e., 100-fold fewer B cells generated expanded clones of PFC in the absence of either one or the other signal.
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More recently, it was discovered t h a t several m u t a n t EL-4 thymoma cell lines obtained from the NIH-EL-4 line constitutively provide a B-cell activation signal(s). Thereby, two lines induced growth factor responsiveness of B cells uniquely in conjunction with anti-Ig, whereas one line acted quite well in the absence of anti-Ig (R. Z. and H. R. MacDonald, unpublished observations). This effect was not mediated by m u t a n t EL-4 supernatant. It is not known at the present time whether the effect of the m u t a n t cells is related to physiologic Th function. However, these observations suggest that the requirement for specific antigens (or anti-Ig) in Th-dependent B-cell activation may depend on the quality of the Th signal and thus align our results with those obtained by Martinez and Coutinho [11]. In any ease, by analysing responses of low numbers of B cells in the absence or presence of defined non-helper T or thymoma filler cells, it was consistently found that anti-Ig alone or together with T-cell factors (present in the supernatants from different cloned Th, T hybridomas or total mixed leucocyte cultures) and/or macrophage factors (P388D1 SN) never led to the induction of B-cell responses [16, 17]. I believe, therefore, t h a t either small numbers of contaminating T cells or mitogenic substances introduced into culture systems with certain batches of foetal calf serum participate in anti-Ig-dependent B-cell activation. 5. - - Conclusions.
Based on the data discussed above, as well as our previous results [10, 13] and those obtained by others [1, 6, 9, 11, 12], it is proposed that an Ia/carrier-specific Th signal which is not bypassed by stable soluble T-cell and macrophage factors is essential for B-cell activation during physiologic B-cell responses. At the present time, it is not known whether the interaction of T-cell antigen receptors with Ia molecules on the B cells directly generates this signal or whether other membrane structures (at the T- and B-cell levels) or some kind of labile short-range mediator are involved. Moreover, it is proposed that the antigen (hapten)/B cell interaction, in addition to its role in focusing the T cells onto the B cells, has a synergistic effect on Th-dependent (as well as LPS-dependent) B-cell activation, i. e. possibly on the expression of specific growth factor receptors by B cells, but t h a t antigens (of the T-dependent type) or anti-Ig antibodies alone do not render the resting B cells responsive to any non-specific T-cell factors. With regard to the important role of non-specific factors in the B-cell response, the rec[uirement for a specific Th signal may represent the safeguard mechanisms for the control of the overall specificity of the response. In addition, B cells need not be tolerant for those self determinants that are not normally associated with determinants recognized by T cells. There is ample evidence that self-reactive B cells exist, and it is likely t h a t a mechanism leading to the elimination of all self-reactive B cells would, in fact, eliminate most of the B cells required for immune defence. Thus, more selective regulatory mechanisms acting at the level of T/B cell interaction m a y normally prevent harmful B-cell auto-reactivity. They remain to be elucidated. Re/erences.
[1] ANDEnSSON, J., SCHRF.IEn, M. H. & MELCHERS, F., T-cell-dependent B-cell stimulation is H-2 restricted and antigen-dependent only at the restin-~ B cell level. Proc. nat. Acad. Sci. ("Wash.), 1980, 77, 1612-1616. [2] MITCHISON,N. A., The carrier effect in the secondary response to hapten-protein conjugates. - - II. Cellular Cooperation. Europ. J. Immunol., 1971, 1, 18-26. [3] RAJEWSKY, K., ROELANTS, G. E. & ASKONAS, B. A., Carrier specificity and the allogeneic effect in mice. Europ. J. lmmunol., 1972, 2, 592-598. [4] KATZ, D. H., HAMAOKA, T. & BENACERRAF, B., Cell interactions between histoincompatible T and B lymphoeytes. - - II. Failure of physiologic cooperative interactions between T and B lymphocytes from allogeneie donor strains in humoral response to hapten-protein conjugates. J. exp. Med., 1973, 137, 1405-1418.
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[5] SeRENT, J., Restricted helper function of F 1 hybrid T cells positively selected to heterologous erythrocytes in irradiated parental strain mice. - - I I. Evidence for restrictions affecting helper cell induction and T-B collaboration, both mapping to the K-end of the H-2 complex. J. exp. Med., 1978, 147, 11591174. 16] MARRAGK,P. & KAPPLER, J. W., The role of H-2-1inked genes in helper T-cell function. - - VII. Expression of I region and immune response genes by B ceils in bystander help assays. J. exp. Med., 1980, 152, 1274-1288. [7] SHIMONKEVITZ,R,, KAPPLER, J., MAnRACK, P. & GREY, H., Antigen recognition by H-2-restricted T cells. - - I. Cell-free antigen processing. J. exp. Med., 1983, 158, 303-316. [8] SCHIMPL, A. & WECKER, E., A third signal in B-cell activation given by TRF. Transplant. Rev., 1975, 23, 176-188. [9] KELLER, D. M., SWIERKOSZ, J. E., MARRACK, P. & KAPPLER, J. W., TWO types of functionally distinct, synergizing helper T cells, d. Immunol., 1980, 124, 1350-1359. [10] ZUBLER, R. H. & GLASEBROOK,A. L., Requirement for three signals in ,r T-independent )~ (lipopolysaccharide-induced) as well as in T-dependent B-cell responses. J. exp. Med., 1982, 155, 666-680. [11] MARTINEZ-A., C. & COUTINHO,A., B-cell activation by helper cells is a two-step process. Nature (Lond.), 1981, 190, 60-61. [12] JuLius, M. H., Von BOEHMER,H. • SIDMAN, C. L., Dissociation of two signals required for activation of resting B cells. Proc. nat. Acad. Sci. (Wash.), 1982, 79, 1889-1993. [13] ZUBLER, R. H. & KANAGAWA, O., Requirement for three signals in B-cell responses. - - II. Analysis of antigen- and Ia-restricted T helper cell-B cell interaction. J. exp. Med., 1982, 156, 415-429. [14] PARKER, D. C., Separable helper factors support B-cell proliferation and maturation to Ig secretion. J. Immunol., 1982, 129, 469-474. [15] NAKANISHI, K., I'IOWARD, M., MURAGUCHI, A., FARRAR, J., TAKATSU, K., HAMAOKA, T. & PAUL, W. E., Soluble factors involved in B-cell differentiation: identification of two distinct T-cell-replacing factors (TRF). J. Immunot., 1983, 134, 2219-2224. [16] ZUBLER, R. H., Polyclonal B-cell responses in the presence of defined filler cells: complementary effects of lipopolysaccharide and anti-immunoglobulin antibodies. Europ. J. Immunol., 1984 (in press). [17] ZUBLER, R. H., Signal requirements for T-dependent and T-independent B cell activation. Lymphokines, 1984, 10 (in press).
INDUCTION OF B LYMPHOCYTES BY H E L P E R T CELLS: R E Q U I R E M E N T OF D I R E C T CELL CONTACT b y C. Martinez-A (*)., A. De La Hera, C. Marquez and P. Pereira (*) Department o/hnmunologg, Clinica Puerta de Hierro, S. Martin de Porres 4, Madrid-35 and (*) Laboratoire d'Immunobiologie, Instilut Pasteur, 75724 Paris Cedex 15 General agreement appears to exist concerning the mechanism involved in clonal expansion and immunoglobulin secretion of B cells. After initial triggering, B lymphocytes become reactive to B-cell-specific polyclonal growth and differentiation factors. While induction mainly involves immunological phenomena, growth and maturation relate to a more general problem in biology [1, 2, 3, 4, 5]. T h e controversy on the nature of the triggering receptor is a reflection of the methodology used in B-cell activation. Classical perspectives are divided into two schools of thought: those centered around the role of antigenic recognition of the responding B-lymphocytes b y immunoglobulin as a necessary requirement
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[28] MONROE, J. G. & CAMBIER,J. C., B-cell activation: B-cell plasma membrane depolarization and hyper-Ia antigen expression induced by receptor immunoglobulin cross linking are coupled. J. exp. Med., 1983, 158, 15891599. [29] RINGDEN, 0. • RYNNEL-DAGo(i,B:, Activation of human B and T lymphocytes by protein A of Staphylococcus aureus. Europ. J. Immunol., 1978, 8, 47-52. [30] PRYJMA, J., MUNOZ, J., GALBRAITH,R. M., FUDENBERG, H. H. & VIRELLA, G., Induction and suppression of immunoglobulin synthesis in cultures of human lymphocytes: effects of pokeweed mitogen and Staphylococcus aureus Cowan I. J. Immunol., 1980, 124, 656-661. [31] SCHUURMAN,R. K. B., GELFAND, E. W. & DOSCH, H.-M., Polyclonal activation of human lymphocytes in vitro. - - I. Characterization of the lymphocyte response to a T-cell-independent B-cell mitogen. J. Immunol., 1980, 125, 820-826. [32] SAIKI, 0. & RALPH, P., Induction of human immunoglobulin secretion. - - I. Synergistic effect of B-cell mitogen Cowan I plus T cell mitogens of factors. J. Immunol., 1981, 127, 1044-1047. [33] FALKOFF, R. J. M., ZHU, LI PING ZJI ~2 FAUCI, A. S., Separate signals for human B-cell proliferation and differentiation in response to Staphylococcus aureus: evidence for a two-signal model of B-cell activation. J. Immunol., 1982, 129, 97-102. [34] YOSHIZAKI, K., NAKAGAWA, T., KAIEDA, T., MURAGUCHI, A., YAMAMURA, Y. & KISI-IIMOTO, T., Induction of proliferation and Ig production in human B leukemic cells by anti-immunoglobulins and T-cen factors. J. Immunol., 1982, 128, 1296-1301. [35] OKADA, M. et at., B-cell growth factors and B-cell differentiation factor from human T hybridomas. J. exp. Med., 1983, 157, 583-590. [36] MURAGUCHI,A. et at., Differential sensitivity of human B-cell subsets to activation signals delivered by anti-~ antibody and proliferation signals delivered by a monoclonal B-cell growth factor. J. exp. Med., 1983, 157, 530-546.
ROLES OF T H E SPECIFIC T - H E L P E R SIGNAL AND T H E A N T I G E N SIGNAL IN B-CELL ACTIVATION b y R. Zubler Swiss Institute for Experimental Cancer Research, 1066 Epalinges s/Lausanne (Switzerland) I. - - Introduction.
I t is now generally accepted t h a t during a humoral immune response, the resting B cells m u s t first receive appropriate activation signals before they can proliferate and differentiate into antibody-secreting cells in response to T-cellderived non-specific soluble growth and possibly differentiation factors [1]. However, the exact nature and role of the activation signals (as of the non-specific factors) is still the subject of controversies. The questions addressed in this s h o r t discussion paper are (1) whether B-cell activation requires an Ia/carrier-specific T-cell signal which cannot be mediated by stable interleukins and (2) whether the interaction of specific antigens (or anti-Ig antibodies) with the surface immunoglobulins of B cells generates an activation signal. 2. - - The specificilg o[ T helper cell/B cell interactions. The occurrence of so-called linked recognition of hapten and carrier determinants b y B cells and T helper cells (Th) [2, 3] in conjunction with H-2 restriction
102
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at the level of T/B cell interactions in vivo as well as in vitro [4, 5, 6], and the capacity of B cells to present antigens to T cells [7] are now well established. In vivo, a specific T/B cell interaction certainly is important for the optimal delivery of non-specific T-cell factors [8] to B cells. However, a requirement for a specific T/B cell interaction can be demonstrated in vitro in well defined culture systems even in the presence of an artificially high concentration of non-specific T-cell factors and, therefore, most likely has additional effects, i. e., provides an essential B-cell activation signal [1, 6, 9-13]. This will be further discussed in the context of recent observations from this laboratory summarized in (( Section 4 ,). 3. - - ElTect o/ B cell~antigen interaction.
Normally, B cells can be recognized by T cells only if the B cells have themselves already recognized some antigen. However, in experimental systems in which the specificity of Th is directed against B-cell membrane antigens rather than conventional antigens, the effect of B cell/antigen (hapten) interaction can be analysed independently of its role in the focusing of Th onto B cells. Using this type of system, some authors obtained high polyclonal B-cell responses in the apparent absence of antigen recognition by the B cells and thus concluded that a specific Th signal is by itself sufficient for B-cell activation [11]. In other studies [12], including those from my own laboratory [13], it was for the generation of optimal antigen-specific (or polyclonal) plaque-forming cell (PFC) responses in the presence of cloned H-Y-specific Th required t h a t the B cells themselves could see specific antigens (or react with anti-Ig antibodies). In addition, with regard to polyclonal B-cell activation systems in current use in different laboratories for the characterization of the non-specific factors acting on B cells, it seems t h a t anti-Ig antibodies alone or together with soluble factors can induce B-cell activation, i. e. in the absence of T cells [14, 15]. If this is true, polyclonal B-cell activation requires either Th alone or anti-Ig alone. In my own recent studies, this has been reinvestigated and the results will be briefly summarized. 4. - - Requirements/or the induction o/growth/actor responsiveness o / B cells [16].
Low numbers of purified B cells (108/200 ~1 or less) were placed into cultures containing different types of irradiated cloned T cells, i. e. subclones derived from H-Y-specific cloned Th which either (a) still provided a male-specific (or ConAmediated non-specific) B-cell activation signal but had lost the capacity to generate B-cell growth factor or (b~ had lost all detectable helper activities. This type of culture system was used to analyse the effects of Th, anti-Ig and/or T-cell factors, firstly because it can be assumed to contain few undefined T cells which m a y contaminate B-cell preparations and, secondly, because only low numbers of B cells can optimally proliferate in a polyelonal system without overgrowing the cultures. It was found that anti-Ig (polyvalent, affinity-purified rabbit anti-mouse Ig coupled to sepharose beads) was capable of and, in fact, was required for inducing growth factor responsiveness of B cells in cultures with ConA and T cells of type a, i. e. the addition of anti-Ig and T-cell supernatants (SN) led to potent thymidine incorporation. However, anti-Ig and T-cell SN did not lead to any response in cultures with Th of type b. In cultures with Th of type b, the addition of lipopolysaccharide (LPS), anti-Ig and T-cell SN together led to a high proliferative response. Thus, the study demonstrated that a ConA-mediated Th signal (which could not be replaced by soluble factors) and anti-Ig or (in cultures without competent Th) LPS and anti-Ig were required for optimal polyclonal B-cell activation. Using a B-cell-limiting dilution assay and measuring the generation of clones of protein-A PFC, it was found t h a t two activation signals provided by Th and anti-Ig (or by LPS and anti-Ig) had to act on the same B cells, i. e., 100-fold fewer B cells generated expanded clones of PFC in the absence of either one or the other signal.
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More recently, it was discovered t h a t several m u t a n t EL-4 thymoma cell lines obtained from the NIH-EL-4 line constitutively provide a B-cell activation signal(s). Thereby, two lines induced growth factor responsiveness of B cells uniquely in conjunction with anti-Ig, whereas one line acted quite well in the absence of anti-Ig (R. Z. and H. R. MacDonald, unpublished observations). This effect was not mediated by m u t a n t EL-4 supernatant. It is not known at the present time whether the effect of the m u t a n t cells is related to physiologic Th function. However, these observations suggest that the requirement for specific antigens (or anti-Ig) in Th-dependent B-cell activation may depend on the quality of the Th signal and thus align our results with those obtained by Martinez and Coutinho [11]. In any ease, by analysing responses of low numbers of B cells in the absence or presence of defined non-helper T or thymoma filler cells, it was consistently found that anti-Ig alone or together with T-cell factors (present in the supernatants from different cloned Th, T hybridomas or total mixed leucocyte cultures) and/or macrophage factors (P388D1 SN) never led to the induction of B-cell responses [16, 17]. I believe, therefore, t h a t either small numbers of contaminating T cells or mitogenic substances introduced into culture systems with certain batches of foetal calf serum participate in anti-Ig-dependent B-cell activation. 5. - - Conclusions.
Based on the data discussed above, as well as our previous results [10, 13] and those obtained by others [1, 6, 9, 11, 12], it is proposed that an Ia/carrier-specific Th signal which is not bypassed by stable soluble T-cell and macrophage factors is essential for B-cell activation during physiologic B-cell responses. At the present time, it is not known whether the interaction of T-cell antigen receptors with Ia molecules on the B cells directly generates this signal or whether other membrane structures (at the T- and B-cell levels) or some kind of labile short-range mediator are involved. Moreover, it is proposed that the antigen (hapten)/B cell interaction, in addition to its role in focusing the T cells onto the B cells, has a synergistic effect on Th-dependent (as well as LPS-dependent) B-cell activation, i. e. possibly on the expression of specific growth factor receptors by B cells, but t h a t antigens (of the T-dependent type) or anti-Ig antibodies alone do not render the resting B cells responsive to any non-specific T-cell factors. With regard to the important role of non-specific factors in the B-cell response, the rec[uirement for a specific Th signal may represent the safeguard mechanisms for the control of the overall specificity of the response. In addition, B cells need not be tolerant for those self determinants that are not normally associated with determinants recognized by T cells. There is ample evidence that self-reactive B cells exist, and it is likely t h a t a mechanism leading to the elimination of all self-reactive B cells would, in fact, eliminate most of the B cells required for immune defence. Thus, more selective regulatory mechanisms acting at the level of T/B cell interaction m a y normally prevent harmful B-cell auto-reactivity. They remain to be elucidated. Re/erences.
[1] ANDEnSSON, J., SCHRF.IEn, M. H. & MELCHERS, F., T-cell-dependent B-cell stimulation is H-2 restricted and antigen-dependent only at the restin-~ B cell level. Proc. nat. Acad. Sci. ("Wash.), 1980, 77, 1612-1616. [2] MITCHISON,N. A., The carrier effect in the secondary response to hapten-protein conjugates. - - II. Cellular Cooperation. Europ. J. Immunol., 1971, 1, 18-26. [3] RAJEWSKY, K., ROELANTS, G. E. & ASKONAS, B. A., Carrier specificity and the allogeneic effect in mice. Europ. J. lmmunol., 1972, 2, 592-598. [4] KATZ, D. H., HAMAOKA, T. & BENACERRAF, B., Cell interactions between histoincompatible T and B lymphoeytes. - - II. Failure of physiologic cooperative interactions between T and B lymphocytes from allogeneie donor strains in humoral response to hapten-protein conjugates. J. exp. Med., 1973, 137, 1405-1418.
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[5] SeRENT, J., Restricted helper function of F 1 hybrid T cells positively selected to heterologous erythrocytes in irradiated parental strain mice. - - I I. Evidence for restrictions affecting helper cell induction and T-B collaboration, both mapping to the K-end of the H-2 complex. J. exp. Med., 1978, 147, 11591174. 16] MARRAGK,P. & KAPPLER, J. W., The role of H-2-1inked genes in helper T-cell function. - - VII. Expression of I region and immune response genes by B ceils in bystander help assays. J. exp. Med., 1980, 152, 1274-1288. [7] SHIMONKEVITZ,R,, KAPPLER, J., MAnRACK, P. & GREY, H., Antigen recognition by H-2-restricted T cells. - - I. Cell-free antigen processing. J. exp. Med., 1983, 158, 303-316. [8] SCHIMPL, A. & WECKER, E., A third signal in B-cell activation given by TRF. Transplant. Rev., 1975, 23, 176-188. [9] KELLER, D. M., SWIERKOSZ, J. E., MARRACK, P. & KAPPLER, J. W., TWO types of functionally distinct, synergizing helper T cells, d. Immunol., 1980, 124, 1350-1359. [10] ZUBLER, R. H. & GLASEBROOK,A. L., Requirement for three signals in ,r T-independent )~ (lipopolysaccharide-induced) as well as in T-dependent B-cell responses. J. exp. Med., 1982, 155, 666-680. [11] MARTINEZ-A., C. & COUTINHO,A., B-cell activation by helper cells is a two-step process. Nature (Lond.), 1981, 190, 60-61. [12] JuLius, M. H., Von BOEHMER,H. • SIDMAN, C. L., Dissociation of two signals required for activation of resting B cells. Proc. nat. Acad. Sci. (Wash.), 1982, 79, 1889-1993. [13] ZUBLER, R. H. & KANAGAWA, O., Requirement for three signals in B-cell responses. - - II. Analysis of antigen- and Ia-restricted T helper cell-B cell interaction. J. exp. Med., 1982, 156, 415-429. [14] PARKER, D. C., Separable helper factors support B-cell proliferation and maturation to Ig secretion. J. Immunol., 1982, 129, 469-474. [15] NAKANISHI, K., I'IOWARD, M., MURAGUCHI, A., FARRAR, J., TAKATSU, K., HAMAOKA, T. & PAUL, W. E., Soluble factors involved in B-cell differentiation: identification of two distinct T-cell-replacing factors (TRF). J. Immunot., 1983, 134, 2219-2224. [16] ZUBLER, R. H., Polyclonal B-cell responses in the presence of defined filler cells: complementary effects of lipopolysaccharide and anti-immunoglobulin antibodies. Europ. J. Immunol., 1984 (in press). [17] ZUBLER, R. H., Signal requirements for T-dependent and T-independent B cell activation. Lymphokines, 1984, 10 (in press).
INDUCTION OF B LYMPHOCYTES BY H E L P E R T CELLS: R E Q U I R E M E N T OF D I R E C T CELL CONTACT b y C. Martinez-A (*)., A. De La Hera, C. Marquez and P. Pereira (*) Department o/hnmunologg, Clinica Puerta de Hierro, S. Martin de Porres 4, Madrid-35 and (*) Laboratoire d'Immunobiologie, Instilut Pasteur, 75724 Paris Cedex 15 General agreement appears to exist concerning the mechanism involved in clonal expansion and immunoglobulin secretion of B cells. After initial triggering, B lymphocytes become reactive to B-cell-specific polyclonal growth and differentiation factors. While induction mainly involves immunological phenomena, growth and maturation relate to a more general problem in biology [1, 2, 3, 4, 5]. T h e controversy on the nature of the triggering receptor is a reflection of the methodology used in B-cell activation. Classical perspectives are divided into two schools of thought: those centered around the role of antigenic recognition of the responding B-lymphocytes b y immunoglobulin as a necessary requirement