Reaginic antibody formation in the mouse. VII. Depression of the ongoing IgE antibody formation by suppressor T cells.

The ongoing IgE antibody formation against ovalbumin (OA) in high responder mice was depressed by i.v. injections of either native or urea-denatured ovalbumin (UD-OA). Adoptive transfer experiments to determine the helper function of spleen cells from the treated animals showed that helper function for both IgE and IgG antibody responses diminished after treatment. Evidence was obtained that treatment suppressed the expansion of IgE-G memory cells. When the same treatment with OA or UD-OA was given to OA-primed mice before the appearance of IgE antibody in their serum, OA-specific splenic suppressor T cells were demonstrable. Thus, the transfer of splenic T cells from treated mice into normal mice suppressed the primary IgE and IgG antibody responses of the recipeints to DNP-OA. It was also found that the transfer of the splenic T cells from UD-OA-treated mice into OA-primed mice depressed ongoing IgE antibody formation in the recipients. The results suggested strongly that the decrease of helper function and the depression of ongoing IgE antibody formation by repeated injections of UD-OA was caused by generation of antigen (OA)-specific suppressor T cells.     

Reaginic antibody formation in the mouse. VII. Induction of suppressor T cells for IgE and IgG antibody responses.

Intravenous injections of urea-denatured ovalbumin (UD-OA) into OA-primed high responder mice suppressed the antibody response not only to the priming antigen but also to subsequent immunization with dinitrophenyl derivatives of OA (DNP-OA). The transfer of normal spleen cells or OA-primed spleen cells into UD-OA-treated animals did not restore the capacity of responding to DNP-OA to form anti-DNP IgE and IgG antibodies. The transfer of splenic T cell fraction from the UD-OA-treated animals into normal syngeneic mice diminished both IgE and IgG antibody responses of the recipients to DNP-OA. The B cell-rich fraction from the same donors failed to affect the anti-hapten antibody response and enhanced anti-cancer (OA) IgG antibody response of the recipients. It was also found that the transfer of T cell-rich fraction of OA-primed spleen cells failed to suppress antibody response of the recipients to DNP-OA. The results indicated that spleen cells of UD-OA-treated mice contained suppressor T cells which are distinct from helper cells. Suppressive activity of T cells in the UD-OA treated animals was specific for OA. The transfer of the T cell-rich fraction failed to suppress anti-DNP antibody response of the recipients to DNP-KLH.     

Immunosuppressive effects of glycosylation inhibiting factor on the IgE and IgG antibody response

Glycosylation inhibiting factor (GIF) was purified from culture filtrates of a T cell hybridoma, 23A4, by affinity chromatography on anti-lipomodulin Sepharose. The factor exhibited phospholipase inhibitory activity upon dephosphorylation. Immunization of BDF1 mice with aluminum hydroxide gel (alum)-absorbed dinitrophenyl derivatives of ovalbumin (DNP-OA) resulted in persistent IgE and IgG antibody formation. However, repeated injections of the affinity-purified GIF into the DNP-OA-primed mice beginning on the day of priming prevented the primary anti-hapten antibody responses of both the IgE and the IgG1 isotypes. Treatment with GIF also diminished on-going IgE antibody formation in the DNP-OA-primed mice. The treatment changed the nature of IgE-binding factors formed by BDF1 spleen cells. Incubation of spleen cells from OA + alum-primed mice with OA resulted in the formation of IgE-potentiating factor, whereas spleen cells of OA-primed, GIF-treated mice formed IgE-suppressive factor upon antigenic stimulation. It was also found that Lyt-2+ T cells in the OA-primed, GIF-treated mouse spleen cells released GIF, which had affinity for OA and bore I-Jb determinant(s). Transfer of a Lyt-1+ cell-depleted fraction of the OA-primed, GIF-treated mouse spleen cells into naive syngeneic animals resulted in suppression of the primary anti-DNP IgE antibody response of the recipients to alum-absorbed DNP-OA, but failed to affect the anti-DNP antibody response to DNP-keyhole limpet hemocyanin. The results indicate that GIF treatment during the primary response to OA facilitated the generation of antigen-specific suppressor T cells.     

Reaginic antibody formation in the mouse. X. Possible role of suppressor T cells in transient IgE antibody responses.

The kinetics of IgE antibody response to alum-absorbed dinitrophenyl derivatives of ovalbumin (DNP-OA) was dependent on the dose of immunogen. A persistent IgE antibody response was obtained when high responder BDF1 mice were immunized with a minimum (0.05 microgram) dose. An increase of the immunogen to 10 microgram depressed IgE antibody responses but enhanced IgG antibody responses of both hapten and carrier specificities. Determination of T helper cell activity and B memory cells after immunization with different doses of antigen indicated that minimum immunogen was favorable for developing helper activity, whereas 1 to 10 microgram immunogen were more favorable than a 0.05-microgram dose for developing both IgE and IgG B memory cells. Nevertheless, neither helper T cells nor B memory cells in the spleen explains a transient IgE antibody response to a high (10 microgram) dose of DNP-OA. Evidence was obtained that immunization with 10 microgram OA induced generation of antigen-specific suppressor T cells, which were not detectable after immunization with 0.05 microgram OA. Transfer of suppressor T cells to DNP-OA-primed mice depressed both anti-hapten and anti-carrier IgE antibody responses. The results suggested strongly that suppressor T cells are involved in a transient IgE antibody response to a high-dose immunogen.     

Reaginic antibody formation in the mouse. IX. Enhancement of suppressor and helper cell activities of primed spleen cells.

Attempts were made to increase the activity of suppressor cells in vitro. Antigen-specific suppressor cells were induced by i.v. injections of urea-denatured ovalbumin (UD-OA) into OA-primed mice. Nonadherent splenic lymphocytes from the UD-OA-treated mice were incubated at 37 degrees C for 24 hr with either OA or OA-bearing macrophages and lymphocytes harvested from the culture were examined for the ability to suppress primary anti-hapten antibody response on nonirradiated mice to DNP-OA. The results showed that the suppressive activity of the lymphocytes increased after culture of the cells with OA or OA-bearing macrophages. Similar results were obtained when nylon column-purified T cell-rich fraction of the lymphocytes were similarly cultured. The suppressive activity was associated with theta-bearing lymphocytes and was specific for OA. Suppressor cells were not induced by the culture of OA-primed lymphocytes with OA. The helper function of splenic lymphocytes from both UD-OA-treated mice and OA-primed mice was enhanced by the culture of the cells with OA-bearing macrophages but not by culture with OA in the absence of macrophages.     

Generation of specific helper cells and suppressor cells in vitro for the IgE and IgG antibody responses.

Normal splenic lymphocytes from BDF1 mice were cultured on ovalbumin (OA)-bearing syngeneic peritoneal adherent cells for 5 days and their subsequent helper function was tested by an adoptive transfer technique. Lymphocytes harvested from the culture were mixed with DNP-KLH-primed spleen cells and transferred into irradiated syngeneic mice followed by challenge with DNP-OA. The results showed that the cultured lymphocytes has helper function for both IgE and IgG anti-DNP antibody responses. Depletion of mast cells and T cells in the peritoneal adherent cell preparations did not affect the generation of helper cells in the culture. The helper function of the cultured lymphocytes was abolished by the treatment with anti-theta antiserum and complement and was specific for ovalbumin. The OA-specific helper T cells were generated in vitro by the culture of a T cell-rich fraction of normal spleen on T cell-depleted OA-bearing peritoneal cells. If the normal splenic lymphocytes or T cell-rich fraction were cultured with 10 mug/ml of OA in the absence of macrophages, cultured lymphocytes lacked helper function. The transfer of splenic lymphocytes or splenic T cells cultured with soluble OA to normal non-irradiated mice, however, suppressed both IgG and IgE antibody responses of the recipients to subsequent immunization with DNP-OA. The suppressor cells were sensitive to anti-theta antiserum and complement and their activity was specific for OA. The cultured cells transferred into normal mice did not suppress anti-hapten antibody response to DNP-KLH. Normal lymphocytes cultured on OA-bearing macrophages and had helper function in adoptive transfer experiments failed to suppress antibody response of non-irradiated recipients to DNP-OA. The results indicate that OA-bearing macrophages primed T cells and generated helper T cells, whereas the culture of normal lymphocytes with soluble OA in the absence of macrophages generated suppressor T cells.     

Regulation of antibody response in different immunoglobulin classes. II. Induction of in vitro IgE antibody response in murine spleen cells and demonstration of a possible involvement of distinct T-helper cells in IgE and IgG antibody responses.

In vitro induction of anti-DNP IgE as well as IgG1, IgG2a antibody responses was shown in murine spleen cell culture. Spleen cells primed three times with 1 mug of DNP-OA or DNP-Asc produced significant amounts of anti-DNP IgE as well as IgG antibodies by the in vitro stimulation with DNP-OA or DNP-Asc, respectively. Collaboration between DNP-primed B cells and carrier-primed T cells was required for the induction of both IgE and IgG antibodies with DNP-coupled T-dependent antigen. Carrier-specific T cells induced with a low dose of Asc (0.01 mug) showed helper function only on IgE antibody response, whereas T cells primed with a higher dose of Asc (10 mug) cooperated only with IgG-B cells. T cells primed with Asc in CFA showed helper function mainly on IgG antibody response but not on IgE antibody response. The result indicated the presence of a distinct population of T helper cells for IgE and IgG antibody responses. T-independent antigen (DNP-Ficoll) induced both anti-DNP IgE and IgG antibody responses in DNP-primed spleen cell population without the requirement of the collaboration of helper T cells.     

Regulation of the murine IgE antibody response. I. Characterization of suppressor cells regulating both persistent and transient responses and their sensitivity to low doses of X-irradiation.

Anti-ovalbumin (OA) IgE antibody responses were measured in B6D2F1 mice as a function of time and antigen dose. One hundred to 200 microgram of OA in Al(OH)3 elicited transient responses, whereas 1 to 10 microgram of OA in Al(OH)3 elicited persistent anti-OA IgE responses of high titer. T cells isolated from the spleens of mice mounting either a persistent or a transient response strongly suppressed primary anti-DNP IgE responses in unirradiated recipient mice that were immunized with DNP-OA in Al(OH)3; it was, therefore, concluded that suppressor T cells (Ts cells) were activated during both the persistent and transient IgE responses. Nevertheless, in the present study it was not possible to completely rule out the contention that IgG antibodies may also have been suppressing the IgE response. With a modified adoptive transfer system, it was shown that these Ts cells were sensitive to low doses (250 R) of x-irradiation. The suppressive activity of long-term OA primed cells was also shown to be markedly enhanced when cultured for 24 hr with soluble OA; this finding was interpreted to indicate the presence of memory suppressor cells.     

Regulatory mechanism of reagin production in mice at the T cell level. I. Suggestive evidence for the generation of class specific PPD-reactive helper T cell population in Mycobacterium-primed cells.

Helper T cell activities specific for purified protein derivative (PPD) generated by immunization with Mycobacterium tuberculosis (Tbc) or PPD were investigated concerning adoptive IgE and IgG antibody responses. It is interesting that preferential triggering activity of IgG antibody response was observed when PPD-reactive cells from mice immunized with Tbc were used as a helper cell source. The selective triggering of IgG B cells by Tbc-primed cells was consistently observed using DNP-primed B cell populations from mice immunized with DNP-carrier conjugate in either ICFA or alum. T cell dependency of helper activity was demonstrated by the fact that treatment of Tbc-primed cells with anti-Thy 1 antiserum plus complement abolished their helper activity. We also demonstrated that purified T cell populations selectively triggerred IgG B cells. Selective triggering of IgG B lymphocytes by Tbc-primed T cells may not be due to the influence of suppressor T cells supposedly present in Tbc-primed cells since this selectivity was not affected by X-irradiation of Tbc-primed T cell populations which may inactivate suppressor T cells. Furthermore, passive transfer of Tbc-primed cells into normal recipient mice, the condition which may detect the suppressor T cell effect much more sensitively in IgE production, or preimmunization with Tbc 2 weeks before, did not suppress primary anti-DNP IgE antibody response to DNP-PPD. Thus, the observations presented here are favorable to the concept of the presence of IgG class-specific helper T lymphocytes. Furthermore, PPD-reactive T cells from mice immunized with PPD itself exerted their helper function for triggering B cells of both IgE and IgG classes. This may also indicate that some of the components associated with Tbc other than PPD might negatively affect the development of PPD-reactive helper T cells specific to the IgE class. The generation of such IgG-specific T cell activity in the presence of Tbc will be discussed in the light of the T cell population involved in the regulation of antibody responses of different immunoglobulin classes.     

Carrier-specific unresponsiveness in reaginic antibody formation. II. Suppression of hapten and carrier responsiveness in presensitized rats.

By inducing carrier-specific tolerance to sheep γ-globulin (SGG) in rats challenged with TNP-SGG in alum, it has been possible to study the effect of helper T-cell Unresponsiveness on IgE anti-TNP antibody formation. Rats primed to either the carrier (SGG) or the hapten (TNP as TNP-KLH) were treated with a single high dose (10 mg) of soluble SGG resulting in a suppression of both IgE anti-TNP and anti-SGG antibody which was maintained following a normally immunogenic secondary challenge with TNP-SGG in alum. This suppression was relatively long lasting, with no detectable IgE responsiveness to hapten or carrier observed for up to 8 weeks after tolerance induction. Suppressed animals were able to respond to the hapten when challenged with TNP-KLH, indicating that the induced effect did not directly involve the IgE antibody producing cells, but rather the carrier-specific helper cells. These results parallel our previous findings for IgM and IgG responses in a similar system. Such relatively long lasting and easily induced suppression in IgE antibody formation to specific protein antigens in primed animals may eventually provide a clinically useful means of allergic desensitization to large protein allergens.     

Carrier-specific suppression of antibody responses by antigen-specific glycosylation-inhibiting factors

We previously established an ovalbumin (OA)-specific T cell clone from spleen cells of BDF1 mice, which had been treated by i.v. injections of OA, and constructed antigen-specific T cell hybridomas from the T cell clone. One of the hybridomas constitutively released glycosylation-inhibiting factor (GIF) which lacked affinity for OA, and was called non-specific GIF. Incubation of the same hybridoma cells with OA-pulsed syngeneic macrophages or OA-pulsed B lymphoblastoid cells of BALB/c origin resulted in the formation of GIF molecules that had affinity for OA but not for bovine serum albumin or keyhole limpet hemocyanin. Both the OA-specific GIF and nonspecific GIF bound to monoclonal anti-lipocortin and possessed I-Jb determinants. The OA-specific GIF consisted of two species of molecules, of m.w. 80,000 and 30,000 to 40,000, respectively, whereas the nonspecific GIF from unstimulated cells had an m.w. of 15,000. Intravenous injections of OA-specific GIF or nonspecific GIF into BDF1 mice suppressed both the IgE and IgG1 anti-hapten antibody responses of the animals to dinitrophenyl derivatives of OA (DNP-OA), but OA-specific GIF was much more effective than nonspecific GIF in suppressing the antibody responses. When the same preparations of GIF were injected into DNP-KHL-primed mice, OA-specific GIF and nonspecific GIF were comparable in suppressing the anti-DNP antibody response. In contrast to the 40,000 m.w. species of OA-specific GIF, the 80,000 m.w. OA-specific GIF had carrier-specific suppressive effects. The similarities of antigen-specific GIF to antigen-specific TsF suggest that the phospholipase-inhibiting activity of the molecules may be involved in the immunosuppressive effects of some antigen-specific TsF.     

Carrier-specific unresponsiveness in reaginic antibody formation. I. Induction of helper cell tolerance in rats.

Rats pretreated with 10 mg soluble sheep gamma globulin (soluble SGG or SGGSo) showed a marked reduction in IgE anti-TNP antibody upon challenge with TNP-SGG in alum. This effect was found to be carrier-specific since SGGSo tolerant rats gave normal IgE anti-TNP responses when challenged with TNP-KLH. Carrier tolerance persisted when a secondary challenge with TNP-SGG was given. The degree of tolerance induction was shown to be tolerogen dose-dependent. As expected, IgE anti-SGG responses were also reduced in this system by pretreatment with SGGSo. These results indicate that carrier-specific helper cells for IgE antibody responses can be rendered functionally unresponsive. However, in contrast to the long duration of carrier-specific tolerance for IgM and IgG responses, IgE tolerance in this system appeared to be only short-lived. This difference suggests that IgE helper and/or suppressor T cells may represent a separate subclass from those involved in IgM and IgG responses.     

Immunogenic properties of modified antigen E. III. Effect of repeated injections of modified antigen on immunocompetent cells specific for native antigen.

It has been shown that ragweed antigen E loses its major antigenic determinants after denaturation in 8 M urea, but urea-denatured (UD) antigen and an alpha-polypeptide chain isolated from the denatured molecules are capable of priming mouse T cells specific for native antigen. Weekly injections of 10mug UD antigen or alpha-chain into antigen E-primed animals depressed the ongoing IgE antibody response, whereas injections of the same dose of antigen E failed to depress the antibody response. It was found by adoptive transfer experiments that helper activity of antigen E-primed splenic T cells was depressed by the treatment of the donors with either modified antigen or native antigen E. The same treatment of antigen E-primed animals depressed the DNA synthetic response of their splenic T cells to antigen E. The treatment of antigen E-primed animals with UD antigen resulted in a decrease of antigen E-specific IgE-B cells and IgG-B cells in their spleen, whereas the treatment with native antigen expanded the B cell populations. In view of the results obtained in the mouse, cellular basis for the immunologic effects of hyposensitization treatment is discussed.     

Fyn Kinase Is Required for Optimal Humoral Responses

The generation of antigen-specific antibodies and the development of immunological memory require collaboration between B and T cells. T cell-secreted IL-4 is important for B cell survival, isotype switch to IgG1 and IgE, affinity maturation, and the development of germinal centers (GC). Fyn, a member of the Src family tyrosine kinase, is widely expressed in many cell types, including lymphocytes. This kinase is known to interact with both the B cell and T cell receptor (BCR and TCR, respectively). While Fyn deletion does not impair the development of immature T cells and B cells, TCR signaling is altered in mature T cells. The current study demonstrates that Fyn deficient (KO) B cells have impaired IL-4 signaling. Fyn KO mice displayed low basal levels of IgG1, IgE and IgG2c, and delayed antigen-specific IgG1 and IgG2b production, with a dramatic decrease in antigen-specific IgG2c following immunization with a T-dependent antigen. Defects in antibody production correlated with significantly reduced numbers of GC B cells, follicular T helper cells (T_FH), and splenic plasma cells (PC). Taken together, our data demonstrate that Fyn kinase is required for optimal humoral responses.     

Elicitation of antigen-induced primary and secondary murine IgE antibody responses in vitro

Described herein are methods for eliciting and quantitating primary and secondary murine IgE antibody responses in vitro, and the important role of antigen concentration in determining the level of IgE produced during an immune response. The methods for quantitating IgE antibody levels in culture supernatant fluids and in serum by ELISA are presented in detail. The specificity of such methods was confirmed in that (1) no other isotype of antibody registered in the IgE-ELISA, and (2) parallel determinations of IgE antibody concentrations could be obtained by independent analysis using Fc epsilon RI-dependent basophil degranulation. We examined various parameters of cell donor immunization and lymphoid cell culture which allow for optimal in vitro primary and secondary IgE responses. High relative antigen doses result in diminished IgE antibody responses in experimental animals, a finding confirmed herein. High antigen concentrations in vitro also result in relative suppression of IgE antibody synthesis. This was also true for in vitro production of IgG1 and IgA antibodies. Conversely, IgM and IgG2a responses were elicited at both low and high antigen concentrations; IgG2b and IgG3 were not produced under the conditions of priming and culture used herein. Finally, production of IgE in vitro depended on the presence of carrier-primed CD4+ T cells and hapten-specific B cells. Generation of maximal IgE antibody secretion, and hence elicitation of an allergic reaction, is thus dependent on the amount of antigen acting as stimulant for the immune response.     

Effect of passive administration of alloantiserum containing antibody against putative acceptor(s) for T cell-replacing factor (TRF) in the neonatal stage on development of B cell activity responsive to TRF

Previously, we showed that the antiserum raised in male (DBA/2Ha X BALB/c)F1(DCF1) mice (T cell-replacing factor [TRF]-low response animals) by immunizing them with activated B cells from BALB/c mice (TRF-high-responders) contained antibodies against putative TRF-acceptor site(s). We have now evaluated the hypothesis that neonatal treatment of mice with the above antiserum suppresses the development of B cells responsive to TRF. Male DCF1 mouse anti-BALB/c B-cell antiserum or normal DCF1 mouse serum as a control was injected into BALB/c mice within 24 hr after birth. In the antiserum-treated mice, no augmented primary immunoglobulin M (IgM) antibody responses to sheep red blood cells (SRBC) were observed under the conditions in which markedly augmented IgM anti-SRBC responses were induced in control BALB/c mice, suggesting that development of B cells reacting with male DCF1 mouse anti-BALB/c B-cell antiserum is suppressed by the neonatal treatment with the antiserum. Furthermore, the development of B cell activity responsible for helper factors derived from T cells, such as TRF, was markedly suppressed in the neonatally antiserum-treated mice, whereas activity of B cells capable of interacting directly with helper T cells through antigen-bridges was not significantly affected by the same treatment. Such suppression of the B cell activity could be induced only when the antiserum was administered within 48 hr after birth. Moreover, neonatal treatment of mice with the antiserum induced suppressed responsiveness of B cells to a T-independent type 2 antigen, TNP-Ficoll. Neither serum-borne suppressive serum components nor suppressor cells were detected by the system employed. These results support the hypothesis that TRF responsive B cells constitute a subpopulation distinct from the other B cells capable of cooperating with helper T cells via cognate interaction.     

Secondary IgG responses to type III pneumococcal polysaccharide. II. Different cellular requirements for induction and elicitation.

Mice primed with a thymus- (T) dependent form of Type III pneumococcal polysaccharide (S3), i.e., S3 coupled to erythrocytes (S3-RBC) produce S3-specific IgG antibody after secondary challenge with either S3 or S3-RBC. The production of IgG antibody by mice challenged with S3 was shown to be T independent since secondary responses were enhanced when mice were treated with anti-lymphocyte serum (ALS) at the time of secondary challenge with S3 and T-depleted spleen cells responded as well as unfractionated spleen cells to S3 in an adoptive transfer system. Secondary S3-specific IgG responses in mice challenged with S3-RBC were shown to be T dependent by the same criteria. The results obtained by using S3 as the antigen indicate that IgG-producing B cells (B lambda cells) can recognize and respond to antigen in the absence of helper T cells. On the other hand, T cells were required for the induction of S3-specific memory B lambda cells since mice depleted of T cells by treatment with ALS at the time of priming with S3-RBC failed to produce S3-specific IgG antibody after secondary challenge with either S3-specific IgG antibody after secondary chall-nge with either S3 or S3rbc. Since RBC-specific memory cells were induced in T-deprived mice the results suggest that T cell regulation of IgG antibody production may vary for different antigens.     

Regulatory mechanism of delayed-type hypersensitivity in mice. I. Properties of memory cpells and suppressor cells for delayed-type hypersensitivity against ovalbumin.

Delayed-type hypersensitivity (DTH) response in mice induced by sc injection of alum-absorbed ovalbumin (OA) was accelerated and enhanced by priming sc with a low dose of urea-denatured ovalbumin (UD-OA), 2 or more days earlier, whereas it was suppressed by priming sc with a high dose of UD-OA, 0 or more days earlier. The ability in primed mice to accelerate or suppress the DTH response could be transferred antigen specifically into cyclophosphamide (CY)-pretreated recipients or normal recipients by spleen cells from primed mice, but not by the T-cell-depleted spleen cells. Furthermore, the ability of spleen cells to transfer the acceleration or the suppression appeared transiently around 7 or 4 days after priming, although the acceleration or the suppression in donor mice persisted for a much longer time. Pretreatment with CY abolished the suppression of DTH response in high dose-primed mice and resulted in the acceleration of DTH response. These results suggest that the activity of DTH-related memory T cells which accelerate and enhance the response can be inhibited by suppressor T cells for the DTH response.     

Sodium periodate-induced suppressor T cells of the human in vitro antibody response

Combinations of T and B lymphocytes from normal individuals booster immunized 14–30 days previously with a combination of diphtheria and tetanus toxoids, synthesized IgG antitetanus toxoid, and IgG antidiphtheria toxoid antibodies when stimulated by pokeweed mitogen in vitro. The addition of 5 μg of soluble tetanus toxoid to the cultures during the first 2 days incubation resulted in greater than 90% suppression of the subsequent production of IgG antitetanus toxoid antibodies. The synthesis of IgM antitetanus toxoid antibodies, total IgG, total IgM, and IgG antidiphtheria toxoid antibodies were unaffected. Similarly, the addition of 5 μg of soluble diphtheria toxoid suppressed the synthesis of IgG antidiphtheria toxoid antibodies with no effect on the synthesis of IgG antitetanus antibodies. Allogeneic combinations of B and T lymphocytes were capable of mediating the suppression, and irradiation of the T cells caused only a partial and variable reversal of the suppression. The antigen-induced specific suppression of antibody synthesis could not be demonstrated in cultures stimulated with soluble T-cell-derived helper factors.