Characterization of human T suppressor-inducer, -precursor and -effector lymphocytes in the antigen-specific plaque-forming cell response

The beneficial effect of donor-specific transfusions: a review of existing explanations and a new hypothesis based on a relatively unapplied theory of T cell immunoregulation. A regulatory hypothesis in progress

The mechanism by which donor specific transfusions protect a graft from the recipient's immune system is unknown. It is likely that this beneficial mechanism is a subset or distinct exhibition of the general rules governing the regulation of the immune system. This phenomenon provides a strong framework for investigation of immune regulation, considering its potential consanguinity to immune regulation, that it is a paradox representing a manifestation of regulatory rules, and that it provides a wealth of clinical experience and experimentation from which to make inferences. Vital in any exploration of immune regulation, is the promise held in reducing the immune system to its chief elemental regulatory mechanisms and interactions. Strangely, the majority of this consequential work may have already been accomplished by Gershon, Green and colleagues with their elegant demarcation of T cell regulation into suppressor and contrasuppressor pathways. The practical and theoretical implications of this discovery seem to be, for the most part, ignored by mainstream immunology. It is doubtful, based on the quality and quantity of their work, or confirming work by other laboratories that they were inaccurate in their findings. It remains a horrible waste that their discoveries are not in immunology's pantheon of hallowed discoveries and are little used. With all this kept in mind, a comprehensive hypothesis of regulation was put together based mainly on Gershon's portrait of the suppressor and contrasuppressor pathways' contributions to immune regulation and experimentation surrounding the unsolved paradox of donor specific transfusions.

Cells and mediators involved in immunoglobulin synthesis by human circulating mononuclear cells. IV. B cells synthesize but do not secrete immunoglobulins because of a defect in the non-T non-B (null) cells

Null cells (non-T and non-B lymphocytes) have previously been demonstrated to be obligatory participants for immunoglobulin synthesis and secretion by normal B cells in culture. Normal null cells have been demonstrated to secrete a factor, human immunoglobulin synthesis/secretion-facilitating factor (HISFF), which can replace the null cells in the culture. In this investigation, the B cells of an 8-month-old male infant and a 46-year-old male adult who presented with a humoral (antibody) immunodeficiency syndrome synthesized immunoglobulin but did not secrete immunoglobulin after culture with pokeweed mitogen and autologous T cells, monocytes, and null cells. In contrast, the patients' B cells synthesized and secreted immunoglobulin after the addition of allogeneic normal null cells or HISFF to the cultures. The same results were obtained with the cells of the infant and the adult patient tested at monthly intervals for 4 months. The results demonstrate that the patients' T cells, B cells, and monocytes functioned normally and that only the patients' null cells were defective. These findings provide an explanation for the absence of immunoglobulin in the circulation of "non(immunoglobulin)secretors," although they possess normal numbers of circulating immunoglobulin-synthesizing B cells. The defect is in the null cell and not in the B cell and consists of the inability of the null cell to secrete HISFF that facilitates the synthesis and secretion of immunoglobulin by the B cell.

CD8+/DR+ T gamma cells inhibit the autologous mixed lymphocyte reaction

The proliferative response of T cells during autologous mixed lymphocyte reactions (AMLR) was affected by depletion of IgG Fc receptor+ T lymphocytes (Tg). Removal of Tg cells resulted in enhanced proliferation, and EA-rosette isolated Tg cells, when added to AMLR cultures as irradiated third components, reduced the uptake of 3H-thymidine by 63-87% in a dose-dependent manner. Negative selection using an avidin-biotin affinity chromatography technique demonstrated that the suppression was mediated by DR+ Tg cells; the major proportion of which also expressed the CD8 antigen. By comparing AMLR supernatants collected from control (lacking Tg) and suppressed (containing Tg) cultures on days 2, 3, and 4, it was established that supernatants from suppressed cultures had significantly reduced levels of cytokine activity. These data indicate that the CD8+/DR+ Tg cells function as suppressor cells during an AMLR and reduce the proliferative response by inhibiting AMLR responder T cells from producing the cytokines necessary for in vitro growth.

Antigen-specific suppressor T lymphocytes in man

The cellular signals that lead to activation of suppressor T cells (Ts) as opposed to cytotoxic T cells (CTL) are unknown. This review describes an in vitro suppressor-induction system developed by us to characterize interactions among various T cells leading to the development of antigen-specific suppression. In this system, antigen-specific CD4+ inducer T cells are first activated with antigen-presenting cells (APC). Antigen-primed CD4+ inducer blasts are then cultured with fresh autologous CD8+ T cells in the absence of the priming antigen. CD8+ T cells isolated from this culture suppress the proliferative response of autologous CD4+ T cells to the priming antigen only. The activated CD8+ Ts lyse neither APC nor antigen-primed CD4+ inducer T cells and can be distinguished from their CD8+CD28+ CTL counterpart by their lack of expression of the CD28 molecule. Furthermore, the ability to induce CD8+ Ts is restricted to antigen-primed CD4+CD29+CD45R-p80+ (Leu8+) T cells. Antibody-mediated inhibition experiments suggest the involvement of CD3/TCR and class I MHC molecules on the surface of CD4+ inducer T cells and the CD2, CD3/TCR, CD8, and CD11a/CD18 molecules on the surface of CD8+ Ts during both the induction and the effector phase of Ts function. Furthermore, compatibility at the class I MHC genes between CD8+ Ts and CD4+ antigen-reactive T cells is required for effective suppression of CD4+ T cells. Together, these results suggest that human antigen-specific CD8+ Ts employ the TCR complex to recognize TCR and class I MHC molecules on the surface of autologous CD4+ inducer T cells during the induction and effector phases of Ts function, and the apparent antigen specificity of suppression reflects specificity for antigen receptors on CD4+ antigen-reactive T cells. This may be a common mechanism by which antigen-specific suppression is accomplished.

Effect of antigen priming on T-cell suppression. I. Activity of Ly 1+2+ feedback suppressor T-cell precursors after isolation from competing Ly 2-T cells

Previous experiments have demonstrated that feedback suppression of murine antibody responses occurs in vitro after exposure of unprimed T-cell subsets to suppression-inducing signals from primed cells, resulting in suppression of primary and secondary IgM as well as IgG anti-SRBC responses. However, following priming with antigen when cells appear which are capable of inducing feedback suppression, the ability of unfractionated splenic T-cell populations to mediate detectable feedback suppression in vitro rapidly disappears, suggesting that priming alters the expression of feedback suppression at the same time as providing for its induction. In the present study, we have succeeded in isolating active feedback suppressor T-cell precursors (preTs) in the Ly 1+2+ and L3T4- T-cell populations from SRBC-primed as well as from unprimed mice, demonstrating that preTs are not lost after priming. The preTs isolated from primed mice resemble those isolated from unprimed mice in Ly and L3T4 phenotype, cell dose requirements, kinetics, level of suppression, and requirement for in vitro activation by primed cells. These results imply that antigen priming neither significantly depresses nor enhances the ability of Ly 1+2+ preTs to participate in feedback suppression and that activated suppressor effector cells are not detectable in the Ly 1+2+ splenic T-cell subset. Priming does, however, induce an enhancing activity in Ly 2-, L3T4+ T cells which appears to compete with feedback suppression and thus may account for the absence of detectable feedback suppression when unfractionated T cells from primed mice are the only source of preTs.

T-cell inducers of suppressor lymphocytes control liver-directed autoreactivity

The sensitisation of helper T cells of patients with autoimmune chronic active hepatitis to a liver-cell membrane-expressed asialoglycoprotein receptor protein is shown to be associated with a defect of T cells that specifically induce suppressor lymphocytes. These lymphocytes are found in an activated state in the peripheral blood of healthy people and may form part of an immunoregulatory network which actively prevents autoimmunity.

Antigen-specific suppression of human antibody responses by allogeneic T cells. II. Cell interactions involved in the generation of suppression

Specific antibody responses to influenza virus were obtained in vitro from human blood mononuclear cells (PBMC). Antibody production in these cultures was profoundly suppressed by the addition of allogeneic T cells with the surface phenotype Leu2a+ (CD8+), Leu8-. Suppression by allogeneic T suppressor (Ts) cells required interactions only between T-depleted B (E-) cells and allogeneic Leu2a+. No evidence was obtained for T-T cell interactions, or for Ts inducer cells similar to those described for nonspecific antibody responses to pokeweed mitogen. Moreover, allogeneic E+, or allogeneic Leu2a+ cells were able to suppress specific antibody responses by E- cells when help was provided by T cell-replacing factor showing that the target of suppression was the responding E- cells, and not T helper cells. In contrast to allogeneic T cells, allogeneic E- cells did not suppress antibody production when added to cultures of unfractionated PBMC (E- + E+). That is, Ts cells activated to allogeneic E- were unable to suppress antibody production by the syngeneic E- cells present in the same culture tube. This result shows that alloactivated Ts cells were specific for the allogeneic E- target cells, and that suppression was not mediated by nonspecific allogeneic effects. Allogeneic Ts cells therefore differ from Ts cells in pokeweed mitogen responses by their specificity, and by their activation in the absence of Ts inducer cells.

Antigen-specific suppression of anti-influenza antibody production in man. Possible role of a membrane-antigen complex

E rosette-forming (E+) cells from human secondary lymphoid tissue were incubated with high dose influenza A virus (Mem-Bel) in an attempt to generate suppressor T cells. Suppression was assayed by transferring the antigen-pulsed E+ cells into effector cultures consisting of E+ and E- cells stimulated with immunogenic amounts of either the inducing virus Mem-Bel) or the non-cross-reacting influenza B virus (B/HK). The transfer resulted in marked inhibition of IgG, IgA and IgM antibody production to Mem-Bel but not to the control antigen, B/HK virus. The suppressive effect was specific at the level of induction as well as expression since E+ cells exposed to high dose Mem-Bel could provide help to an effector culture containing E- cells and optimal dose of B/HK virus. However, metabolically active cells did not appear to be required for suppression. Thus, it could be elicited (a) after only 15 min incubation of E+ cells with high-dose virus and (b) by E+ cells exposed to irradiation, incubated in the presence of metabolic inhibitors, or disrupted by repeated freeze thawing. In contrast, treatment of E+ cells with pronase reversed the suppressive effect. Interestingly, virus heated to 70 degree C failed to induced suppression, while retailing the ability to elicit a normal helper response. Suppression induced by exposure to standard amounts of high-dose antigen was mediated by T cells of both helper/inducer (Leu-3a+) and suppressor/cytotoxic subsets (Leu-2a+), but not by B cells. Two groups of observations pointed to the B cell as the target of suppression. First, suppression could still be transferred to effector cultures in which helper T cells had been replaced by T cell-replacing factor or suppressor T cells removed by irradiation. Second, significant inhibition of antibody production was obtained when the transfer of antigen-pulsed E+ cells was delayed for up to 120 h after initiation of the effector culture. Taken together the results suggest that suppression in this system is due to the formation of an antigen bridge between specific receptor sites on the T cell membrane and the target. Although not dependent on triggering of metabolically active suppressor T cells the phenomenon highlights the need for care in interpreting the mechanism of suppression by high-dose antigen and could, in addition, represent a biologically important control mechanism capable of rapid inhibition of effector T cells and B cells in sites of high antigen concentration.

Enzyme analysis of autologous rosette-forming cells

Autologous rosette-forming cells (ARFC) have been considered to be post-thymic precursor cells. Since thymocytes and peripheral T lymphocytes differ considerably in lactate dehydrogenase isoenzyme pattern and in activity of the enzymes of the purine metabolism, we investigated the enzyme profile in the ARFC. The L-lactate: NAD+ oxi-reductase analysis showed an isoenzyme pattern that closely resembled the pattern found in peripheral T lymphocytes and was totally different from the thymocytes. The levels of adenosine deaminase and purine nucleoside phosphorylase were identical to those found in the peripheral T lymphocytes and different from thymocytes. In our hands, the ARFC-enriched suspension contained predominantly OKT4+ and T mu+ lymphocytes. We propose that ARFC are a heterogeneous population encompassing all known subsets and cannot be considered a separate homogeneous entity.

Immunoregulatory T cell subpopulations in man: dissection by monoclonal antibodies and Fc-receptors

Until now, most of the studies on regulatory T cells have been based on culture systems in which human peripheral blood cells are stimulated by polyclonal stimulators like Pokeweed Mitogen (PWM). Our present contribution, however, deals with T cell-mediated regulation of the antigen-induced B cell activation, which exclusively leads to an antigen-specific IgM production (Heijnen et al. 1979a). Some authors' reports on regulatory activities of T cells, as tested in systems using polyclonal stimulators, differ from ours. This may be due to: a) as a result of polyclonal stimulus, various types of regulatory T cells are activated at the same time b) in contrast to a primary antigen, a polyclonal stimulator induces a rapid proliferation of the various regulatory T cells c) a polyclonal stimulator induces the differentiation of B cells in various maturational stages, that might each require additional or different regulatory signals. For example, Thomas et al. (1981) have shown that freshly isolated T4+ cells can induce suppressor activity in unprimed T8+ cells in the presence of PWM, whereas T4+ cells, precultured for 24 h in the presence of PWM, can exert a suppressor activity themselves without an apparent need for T8+ cells. In the antigen-specific system, however, we have neither been able to detect T suppressor effector activity in a population of primed T4+ cells, nor been able to demonstrate T suppressor inducer activity in unprimed T4+ cells (Heijnen et al. 1982a). Therefore the state of activation of the total T4+ population will dictate the balance of the total T helper and T suppressor activity. As a result of proliferation induced by polyclonal mitogens, small subsets of regulatory T cells, which are functionally undetectable in the primary antigen-specific assay, can expand sufficiently to have a measurable effect. Thomas et al. (1980) have shown that the T4+ suppressor inducer cell in the PWM system is radio-sensitive, which is in contrast with our data in the antigen-specific system. This may imply that we are looking at different subsets of T suppressor inducer cells in these different systems, but it might also indicate that T suppressor inducer cells need to proliferate in order to be able to measurably regulate the large pool of responding cells generated in the PWM system. Apart from such quantitative effects, polyclonal B cell activators like PWM are capable of inducing the differentiation of B cells in various maturational stages (Kuritani & Cooper 1982, Stevens 1982, Peters & Fauci 1983). Since it is highly likely that the regulation of these various B cell subsets might require different regulatory signals, the PWM model might be a very complicated model to study regulatory effects of single T cell subsets.(ABSTRACT TRUNCATED AT 400 WORDS)

Antigen-specific plaque-forming cell response of human cord blood lymphocytes after in vitro stimulation by T cell-dependent antigens

Mononuclear cells isolated from human cord blood (CBL) of full-term neonates were stimulated in vitro with a dose range of T cell-dependent antigens, i.e. ovalbumin or sheep erythrocytes, and tested for the capacity to mount an antigen-specific plaque-forming cell (PFC) response. Both of the antigens used induced in CBL a PFC response with the same kinetics of PFC formation and of the same magnitude as found in cultures of adult peripheral blood lymphocytes (PBL). However, optimal PFC responses in CBL were obtained at a hundredfold lower concentration of the antigens compared with the optimal antigen doses for the induction of a PFC response in adult PBL. This phenomenon was further investigated with respect to the antigen dose dependency of the activation of neonatal B cells and neonatal regulatory T cells. The induction of a PFC response in CBL at antigen concentrations that were suboptimal for adult PBL showed a correlation with the particular antigen dose requirements for the activation of B cells and T helper cells in neonates. Furthermore, the findings suggest that the decrease of the PFC response in CBL stimulated with supraoptimal doses of antigen was not caused by the induction of unresponsiveness at the B cell level or by interference of pregnancy-associated substances with the PFC response, but was rather the result of the activation of antigen-specific T suppressor cells. Neonatal T suppressor cells were activated at antigen concentrations that generated T helper activity in the adult. Thus, although neonatal B cells possess the intrinsic capacity to mature into antigen-specific PFC, the conditions for effective activation of neonatal T cells regulating the B cell response differ from those for the activation of adult regulatory T cells.