Characteristics and mechanisms of action of the concanavalin A-activated suppressor cell in man.

Human peripheral blood lymphocytes treated for 24 to 48 hr with optimally mitogenic doses of concanavalin A suppressed the proliferative response of autologous T cells to mitogens and antigens. Con A-treated cells also suppressed the proliferative response and the immunoglobulin synthetic response of autologous B cells stimulated in vitro by T cell helper factor. The human Con A suppressor cell was sensitive to treatment with mitomycin C and to exposure to radiation doses exceeding 1000 rads. The Con A suppressor cell was shown to reside in the nylon wool-nonadherent, sheep red cell rosette-forming, histamine receptor-bearing population of lymphocytes and to lack surface DRW antigens. One mechanism of action of Con A suppressor cells was shown to be the inactivation of nonspecific T cell helper factor.     

Inhibition of murine suppressor cell function by progesterone

The effects of progesterone on murine suppressor cell function generated in allogeneic MLCs were investigated. BALB/c splenic lymphocytes stimulated in vitro with C3H/He cells significantly suppressed the proliferative response of BALB/c lymphocytes in a secondary MLC. This suppression was highly specific for the sensitizing alloantigens since the suppressor cells had no effect on the proliferative response of BALB/c lymphocytes to third-party alloantigens. In addition, BALB/c lymphocytes stimulated with syngeneic cells were observed to nonspecifically suppress the MLC response to a lesser extent. One to 10 micrograms/ml progesterone added at initiation to suppressor cell generating cultures diminished the ability of both alloantigen specific and nonspecific suppressor cell populations to suppress the proliferative response of homologous lymphocytes to alloantigens. Experiments with pyrilamine, an antihistamine, which blocks cytotoxic T lymphocyte (CTL) generation, suggests that progesterone has a direct inhibitory effect on suppressor cell function independent of its ability to block CTL induction. The effects of progesterone on suppressor cells were not due to shifts in peak response time in MLC or induction of radiosensitive cells in progesterone-treated cultures. Estradiol at doses between 5 and 10 micrograms/ml, and cortisol at dose of 1 microgram/ml, also significantly inhibited suppressor cell function. These results suggest that the steroid hormone milieu within the placenta may effect the activity of allogeneic or nonspecific suppressor cell activity.     

Functional properties of a lymphocyte subpopulation responding to low suboptimal doses of concanavalin A

Incubation of human peripheral blood lymphocytes with concanavalin A (Con A), in a low suboptimal dose (0.5 microgram/ml), results in formation of the cells that inhibit proliferation of autologous cells in cultures activated with optimal but not with suboptimal dose of the mitogen. Nevertheless, 50 micrograms/ml Con A-activated cells efficiently suppress proliferation everywhere. Cell preincubation during 18 h before Con A activation leads to a reduction of lymphocyte responses to the mitogen in cultures reactivated with 5 micrograms/ml Con A in a mixture with autologous lymphocytes, containing no mitogen. Activation of T-T helper cells providing suppressor T cells differentiation seems to take place in the presence of a low suboptimal dose of Con A. Besides, 0.5 microgram/ml Con A prevents the preincubation-induced elimination of some lymphocytes responding to an optimal dose of Con A and autologous lymphocytes.     

Interleukin 2-mediated immune interferon (IFN-gamma) production by human T cells and T cell subsets

Human interleukin 2 (IL 2, or T cell growth factor), which was free of lectin and interferon activity (IFN), induced human peripheral T lymphocytes to produce immune IFN (IFN-gamma). In contrast, non-T cells and macrophages did not produce IFN-gamma in response to IL 2. IL 2 acted directly on unstimulated T cells to induce IFN-gamma production, and also acted in synergy with a suboptimal dose (2 micrograms/ml) of concanavalin A (Con A) to enhance IFN-gamma production. The IFN-gamma-inducing activity of partially purified IL 2 was absorbed along with the IL 2 activity by murine IL 2-dependent CT-6 cell line cells. This further supports the view that IFN-gamma-inducing activity is identical to IL 2. When T cells were separated further into helper/inducer T4+ and suppressor/cytotoxic T8+ subsets by negative selection with monoclonal antibody and complement, both T4+ and T8+-enriched cells produced significant levels of IFN-gamma in response to IL 2. Complete removal of macrophages from purified T lymphocyte populations by treatment of OKM1 plus complement consistently reduced IFN-gamma production in response to IL 2 to a limited degree; readdition of macrophages restored IFN-gamma production by both T cell subsets. This observation that IL 2 contributes to the production of IFN-gamma by human lymphocytes suggests that a cascade of lymphocyte-cell interactions participates in human immune responses.     

In vitro immune response of human peripheral lymphocytes. II. Properties and functions of concanavalin A-induced suppressor T cells.

Con A-stimulation of human peripheral T lymphocytes induced both suppressor and helper T cells. ConA-generated suppressor T cells inhibited PWM-induced IgG and IgM production in PBL. Lower concentrations of Con A (0.5 micrograms/ml) or shorter incubation periods (6 to 24 hr) induced mainly helper T cells, while higher concentrations of Con A (10 micrograms/ml) or longer incubation periods (at least 48 hr) induced suppressor T cells. Con A-generated suppressor T cells were sensitive to mitomycin treatment and exerted their suppressor function on the early phase of differentiation and/or proliferation of B cells but not on the final differentiation of B cells to Ig-producing cells. The identity of the MHC was not required for the expression of suppressor function. Suppressor T cells competed with helper T cells in PWM-induced Ig-production of PBL. This experimental system can be applied to estimate the regulatory function of T cells in several disease states.     

The mitogenic activity of staphylococcal enterotoxin B (SEB): a monovalent T cell mitogen that stimulates cytolytic T lymphocytes but cannot mediate their lytic interaction

Staphylococcal enterotoxin B (SEB), a monovalent T cell mitogen and inducer of T suppressor cells, was found to be a potent polyclonal activator of cytolytic T lymphocytes (CTL) effective against concanavalin A (Con A)-treated target cells. In addition to polyclonal stimulation of CTL, SEB could reactivate "memory" CTL, alloimmunized 60 to 90 days earlier, into "secondary" CTL detectable as early as 24 hr after onset of stimulation and specific for the original priming target cells. Optimal cytolytic activity was induced at 0.5 to 10 micrograms/ml SEB; optimal priming time was 3 days, correlating well with the proliferative activity and morphologic transformation of small lymphocytes into large T lymphoblasts. Long-term cultures of splenocytes, stimulated by SEB, continued to express high cytolytic activity. It is noteworthy that although SEB and Con A are comparable CTL inducers, SEB, unlike Con A, is an ineffective mediator of nonspecific, CTL/target cell interactions. To the best of our knowledge this is the first example of a CTL inducer unable to mediate CTL-target interaction and lysis. The latter observations suggests that different receptors are involved in CTL activation and in CTL-target interaction resulting in lysis.     

Suppressor cells function in healthy persons

The investigations were performed on lymphocytes isolated from peripheral blood of 26 healthy persons aged from 20 to 68 years. The following parameters were evaluated: T suppressor cell activity in two-step culture, concanavalin A (Con A) responsiveness in three-day culture and number of T lymphocytes carrying receptor for Fc portion of immunoglobulin G (TG cells). A slight increase in T suppressor activity and diminished responsiveness to Con A have been shown to be age-dependent. A correlation has been found between suppressor cells activity in vitro and the percentage of TG cells (r = 0.62, p less than 0.05). The level of suppressor activity of lymphocytes was independent of their Con A responsiveness.     

The role of regulatory components from resident T lymphocytes in polyclonal B cell activation

Resident T lymphocytes have been found to exert helper and suppressor regulatory influences with regard to polyclonal activation of murine splenic B lymphocytes elicited by lipopolysaccharide. In the normal adult spleen, only T cell helper influences are exercised over polyclonal B cell activation. This activity is a property of Lyt 1+2- T cells and does not appear to be subject to MHC restriction. Suppressive influence evidently is either latent or it exists at such a low level that its effects are difficult to detect. No regulatory activity can be recovered from the supernatants of T cells, cultured either with or without LPS. However, suppressor T cell function may be evoked by activating splenic T cells with Concanavalin A or by sonicating unstimulated splenic T cells in order to liberate a suppressive potential which is not expressed by these unstimulated cells when intact. The soluble fraction of resident splenic T cell sonicates exerts both helper and suppressor regulatory influences. The soluble helper activity is derived from Lyt l+2- T cells, whereas suppressor activity is generated from Lyt 1-2+ T cells. The suppressive activity of T cell sonicates is not restricted by the MHC gene complex. Helper and suppressor activities contained in splenic T cell sonicates were separated by gel chromatography; the suppressive activity was found to elute with a molecular weight between 68,000 and 84,000 daltons, and the helper activity eluted with a molecular weight between 15,000 and 23,000 daltons. The data indicate that helper and suppressor activities are distinct molecular entities derived from distinct splenic T lymphocyte subpopulations. The possibility that these molecules are precursors to or components of antigen-specific or nonspecific helper and suppressor factors described in the literature is discussed.     

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.     

Patients treated for amebic liver abscess develop cell-mediated immune responses effective in vitro against Entamoeba histolytica

We studied the afferent and efferent cell-mediated immune response in 15 patients treated for amebic liver abscess. Patients had a lower T4 to T8 ratio (1.25 +/- 0.65) compared with age- and sex-matched controls (1.89 +/- 0.44, p less than 0.01) due to a decrease in T4-"helper" cells and an increase in T8-"suppressor" cells (p less than 0.01). The in vitro proliferative response of patient T lymphocytes to the plant mitogen concanavalin A (Con A) was depressed; responses to phytohemagglutinin were not. The proliferative response of patient lymphocytes to an amebic soluble protein preparation (SPP) was greater than the mitogenic response seen in control lymphocytes (mean of 68,300 delta cpm and 22,300 delta cpm, respectively, p less than 0.001), correlated with the T4 to T8 ratio (p less than 0.05) and the duration of time from initiation of antiamebic therapy (p less than 0.01). Supernatants from patient lymphocytes exposed to the amebic SPP activated normal monocyte-derived macrophages to kill virulent axenic E. histolytica trophozoites (p less than 0.001); patient monocyte-derived macrophages activated by Con A-elicited lymphokine could also kill amebae. Finally, when incubated with the amebic SPP for 5 days, T lymphocytes from patients were able to kill virulent amebae (p less than 0.005); patient T lymphocytes not exposed to the amebic SPP or control T lymphocytes incubated for 5 days with the amebic SPP were not cytotoxic to E. histolytica trophozoites. In summary, after cure of amebic liver abscess, specific cell-mediated immune mechanisms develop that are effective in vitro against the parasite.     

Lysozyme-induced inhibition of the lymphocyte response to mitogenic lectins

Both human lysozyme (HL) and hen egg white lysozyme (HEWL) inhibited the proliferative response of peripheral blood lymphocytes to T cell mitogens such as the lectins phytohemagglutinin and concanavalin A. This inhibition was observed both when HL or HEWL was added to the lymphocyte cultures in combination with phytohemagglutinin or concanavalin A and when lymphocytes were pretreated with either lysozyme and extensively washed prior to culture with mitogens. Under both conditions, the effects were strictly dose dependent; the lysozyme concentrations yielding maximal inhibitory effect were 5 micrograms/ml for HL and 1 microgram/ml for HEWL, while both lower and higher concentrations were less effective. Specific antilysozyme rabbit sera completely prevented the inhibitory effects of both HL and HEWL on the proliferative response of lymphocytes to phytohemagglutin or concanavalin A. Chitotriose (a lysozyme inhibitor) caused a strong reduction in the inhibitory effects of the two lysozymes on the lymphocyte response to either lectin. HL and HEWL also were found to markedly inhibit the polyclonal B cell proliferation and differentiation induced by pokeweed mitogen and T cells. A less marked inhibition was also obtained when T cells, but not B cells, were pretreated with HL or HEWL. Again, as in the experiments with T cell mitogens, the effects were dose dependent and 5 micrograms/ml HL and 1 microgram/ml HEWL proved to be the most effective concentrations. The possible mechanisms by which lysozyme inhibits the lymphocyte response to mitogenic lectins are considered and discussed. The enzymatic activity seemed to perform an essential function, as shown by the loss of effect when the heat- or trypsin-inactivated lysozymes were used and by the fact that only the enzymatically active compound, among certain semisynthetic derivatives of HEWL, inhibited the lymphocyte response to the mitogens. However, the cationic properties of the lysozyme molecule appeared to be essential too, since enzymes with a similar specificity of action showed effects similar to those observed with HL or HEWL only when they carried a strong positive charge. It is suggested that lysozyme, which is naturally secreted by monocytes and macrophages, might interact with lymphocyte surface receptor sites and participate in the complex mononuclear phagocyte-lymphocyte interactions and in the modulation of lymphocyte activation.     

Characterization of the spreading process in human T lymphocytes

Substratum-bound concanavalin A (conA) caused attachment and spreading of human T lymphocytes identified by monoclonal anti-T cell antibodies and sheep erythrocyte rosette formation. The simultaneous presence of conA in the medium increased the spreading, whereas preincubation of the cells with conA inhibited spreading. The tendency of conA to induce spreading was dependent on the concentration used, the higher the conA concentration the more pronounced was the spreading. For example, conA at 10 micrograms ml-1 triggered the formation of prominent substratum-attached filopodia with a length of 1-10 micron in 60-80% of T-enriched lymphocytes obtained from separate individuals. At the same conA dose the filopodia were, in 10-20% of the lymphocytes, accompanied by development of lamellipodia. With conA at 100 micrograms ml-1 the number of cells that underwent pronounced spreading was 55-90% in separate individuals. Observation of T-enriched cells fixed at different times after initiation of spreading induced by conA at 100 micrograms ml-1 indicated that filopodia formation represented the initial morphological alteration during the spreading process. This process thereafter proceeded with development of lamellipodia, extensive cytoplasmic spreading and flattening of the central cell mass. Quiescent and mitogen-activated cells exhibited the same sequence of changes during spreading. Spreading led to disappearance of the microvilli with a length of 0.1-0.7 micron present on lymphocytes in suspension, although some microvilli persisted over the cell center.     

Suppressor T cell activation by human leukocyte interferon

Murine fibroblast interferon (IFN beta) activates murine suppressor T lymphocytes in vitro, which suppress plaque-forming cell responses by spleen cells. Suppression of human in vitro immune responses by IFN was investigated to determine whether human IFN also activates suppressor T cells. Human leukocyte IFN (IFN alpha) suppressed pokeweed mitogen-induced polyclonal immunoglobulin production by human peripheral blood mononuclear cells (PBMC) by 80 to 90% at doses of 200 to 350 U/ml. Responses by IFN alpha-treated PBMC were suppressed in a dose-dependent manner; control cultures had maximal responses on day 7. PBMC incubated with 10,000 U/ml of IFN alpha contained activated suppressor cells that decreased pokeweed mitogen-stimulated, polyclonal immunoglobulin production by autologous cells by 70 to 80%. Suppression mediated by these cells was prevented by catalase, ascorbic acid, and 2-mercaptoethanol (2-ME). In murine systems, these reagents interfere with expression of suppressor T cell activity by preventing activation of soluble immune response suppressor. Selection procedures with monoclonal antibodies identified the suppressor cell as an OKT8+ (suppressor/cytotoxic) T lymphocyte. Selected OKT8+ cells required less IFN alpha (1000 U/ml) for activation and were effective in smaller numbers than unfractionated activated PBMC. IFN alpha-activated suppressor cells also inhibited proliferation in mixed lymphocyte and mitogen-stimulated PBMC cultures; again, catalase and 2-ME blocked suppression. These results indicate that IFN alpha activates suppressor T cells in human PBMC cultures; the ability of catalase, 2-ME, and ascorbic acid to block suppression suggests that these suppressor T cells have certain similarities to IFN beta or to concanavalin A-activated murine suppressor T cells.     

Functional characterization of T lymphocytes grown in semisolid agar

T lymphocyte colony forming cells (TL-CFC) grown in agar in the presence of PHA were assayed for their capacity to induce or suppress polyclonal PWM dependent B lymphocyte differentiation into plasma cells. This was measured by identifying cells containing intracytoplasmatic immunoglobulins by direct immunofluorescence. To validate the helper and suppressor system used in this paper, the inductive capacity of unfractionated T lymphocytes and their subpopulations bearing Fc-receptors for IgM (TM) and for IgG (TG) was measured. The unfractionated T cells and the TM fraction showed helper activity, whereas the TG cells expressed suppressor activity. The TL-CFC grown in agar in the presence of PHA manifested helper activity at low cell concentration. However, increasing the TL-CFC concentration finally caused suppression of B cell differentiation. The suppressor effect could be abolished by prior irradiation of the TL-CFC before seeding them in agar. These results indicate that T cells grown in agar have the functional capacity of T helper and T suppressor cells to induce and suppress polyclonal PWM dependent B lymphocyte differentiation into plasma cells.     

Enhancement by irradiated T cells of human plasma cell production: dissection of helper and suppressor functions in vitro.

The addition of irradiated T-enriched lymphocytes to B cell-enriched fractions of human peripheral blood or to unseparated mononuclear cells stimulated the differentiation of plasmacytoid cells in culture with pokeweek mitogen beyond the synergy obtained by the addition of unirradiated T cells. This stimulation was observed in both the proportion and absolute number of plasmacytoid cells recovered from the cultures, and in the amount of IgM detected in culture supernatants by a hemagglutination inhibition assay. Irradiation-induced enhancement was observed with normal and hypogammaglobulinmic T cells, but not with monoclonal T cells from two patients. Inactivation of T cells by heating or by repeated freezing and thawing did not produce the same effects as did irradiation. These data suggest that cell-mediated suppressor function in man is selectively radiosensitive, while helper activity is not. Irradiation may be a useful method for the functional isolation of helper cells and for the manipulation of the balance between suppressor and helper cell activities.     

Decline in the production of interleukin-3 with age in mice

Previously, we and others have found that the ability to produce interleukin-1 (IL-1) and interleukin-2 (IL-2) declines with age in mice. The purpose of this study was to determine the influence of age on the capacity of mice to produce interleukin-3 (IL-3). Splenic cells (5 X 10(6)/ml) from young (3-4 months) and old (24-32 months) C57BL/6 mice were first assessed for their IL-3-producing capacities in response to varying doses of concanavalin A (Con A; 2-20 micrograms/ml) in a time-dependent manner. The results showed that the production of IL-3 by both young and old C57BL/6 mice was maximal on Days 3 and 4 in response to 20 micrograms/ml of Con A, and that of IL-2 was minimal (activity was less than 0.1 unit) on Day 4. Consequently, Day 4, was selected to assess the effect of age on IL-3 production by splenic cells. The results showed a twofold reduction in IL-3 production with age (P less than 0.05). Young-old splenic cell mixture experiments at ratios of 1:0, 3:1, 1:1, 1:3, and 0:1 indicated that the decrease in IL-3 production with age was not due to an increase in suppressor cell activity. Experiments based on mixtures of nylon wool-enriched splenic T-cell and adherent cells and on anti-MAC-1 plus complement-treated spleen cells indicated that (a) adherent cells are not required for T-cell production of IL-3, unlike IL-2 production, and (b) the decrease in IL-3 production with age is due solely to alteration in IL-3-producing T cells. Finally, a strong correlation was demonstrated between the production of IL-2 and IL-3 by spleen cells of individual young and old mice (r = 0.92, P less than 0.01). That production of both IL-2 and IL-3 is affected in a similar manner by age would suggest that a single class of helper T cells may be responsible for production of both lymphokines.     

Regulation of the immune response against UV-induced skin cancers: specificity of helper cells and their susceptibility to UV-induced suppressor cells

The purpose of this study was to determine the role of T helper (Th) cells in the immune response to UV-induced tumors. Repeated exposure of mice to UV radiation results in the production of suppressor T lymphocytes that facilitate tumor growth by inhibiting host immunity. To investigate whether the suppressor T cells inhibit the response to UV tumors by blocking the generation of Th, we employed an indirect method for measuring helper cell activity. We found that Th were produced in normal mice after immunization with UV-induced tumors. These Th appeared to be specific for the immunizing tumors, in contrast to the UV-induced suppressor cells, which recognize UV-induced tumors as a group. The suppressor T cells responsible for inhibiting tumor rejection have no effect on tumor-specific helper cell activity in vitro. However, UV-induced suppressor T cells transferred into unirradiated mice seem to block the generation of helper cell activity after immunization with UV-produced tumors. These results suggest the UV-induced suppressor cells may prevent tumor rejection by blocking the generation of Th.     

Suppression of the polyclonal B-cell responses by concanavalin A-treated bone marrow B cells in vitro

A suppressor cell that inhibits the development of a polyclonal antibody response of splenic B cells to lipopolysaccharide is generated in the bone marrow cell culture in response to a mitotic dose (10 micrograms/ml) of concanavalin A (Con A). The Con A-responding suppressor cell is radioresistant and found in a bone marrow B (BM-B) cell population of normal as well as athymic mice. The suppressor activity of Con A-treated BM-B cells was consistently higher (P less than 0.01-0.0001) than those of untreated BM-B and fresh BM cells. The BM-B cell population recovered from short-term (3-day) cultures with Con A contained about 65% surface immunoglobulin (Ig)-positive cells, about 6% T cells, and less than 0.5% plastic-adherent cells, the latter two of which did not contribute to the suppressive activity. Thus, cytolytic treatment with various anti-T-cell antibodies could not eliminate the suppressive activity of the Con A-treated BM-B cells, and the Con A-treated macrophage population provided no significant suppression. The Con A-treated BM-B cells adherent to anti-Ig or anti-Con A dishes exhibited highly enriched suppressive activity. It was therefore concluded that an immature B-cell population of bone marrow could develop in response to stimulation with Con A into surface Ig-positive suppressor cells, contributing to the regulation of nonspecific B-cell responses.     

Serologic and immunochemical characterization of HLA-A9 xenoantisera

There was a pronounced quantitative difference between the helper activities of B6C3F1 splenic T cells sensitized with unmodified vs modified antigens of SRBC. Modified SRBC induced the greater helper activity which was measured by the magnitude of an anti-TNP response (IgM and IgG) elicited in vivo by virgin B lymphocytes. Antigen modification was produced by conjugating SRBC with the hapten or simply by incubating SRBC in cacodylate buffer. There were restrictions with respect to both erythrocyte species and mouse strains for this differential priming to occur. The relatively poor performance of SRBC-primed T lymphocytes was apparently not due to suppressor T cells, but rather to activation of only one of two identified T cell subpopulations required for full helper activity. Unmodified SRBC activated a subpopulation of "helper" cells characterized as sensitive to elimination by ATS and long-lived after ATx, but failed to activate in B6C3F1 mice a second subpopulation of "amplifier" cells resistant to elimination by ATS and short-lived after ATx. In contrast, modified SRBC activated both helper and amplifier cells. Under appropriate conditions these subsets of T cells were strongly synergistic in promoting antihapten antibody formation especially of the IgG class. The involvement of two distinct types of T lymphocytes in the positive regulation of antibody responses raises interesting and novel questions concerning the sequence of events in the triggering of B cells and the subsequent development of the response.     

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.