Suppressor cells: dependence on assay conditions for functional activity

A review of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced changes in immunocompetence: 1991 update

2,3,7,8-tetrachlorodibenzo-p-dioxin, more popularly called dioxin or TCDD and referred to in this review as 2,3,7,8-TCDD, is considered the prototype of the polychlorinated dibenzo-p-dioxins (PCDD). The PCDD are true contaminants and are formed primarily as byproducts in the manufacture of materials requiring the use of chlorinated phenols and during the combustion of chlorinated chemical products. From an environmental perspective, the PCDD have been most closely associated with the use of a number of phenolic herbicides, including Agent Orange, which is a 1:1 mixture of the butyl esters of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). 2,3,7,8-TCDD and related PCDD are not produced commercially except in small amounts for research purposes and to date, have no known human benefit. 2,3,7,8-TCDD has been demonstrated to be the most potent and the most biologically active congener among the halogenated aromatic hydrocarbons (HAH), which include polychlorinated and polybrominated biphenyls (PCB and PBB, respectively) and the polychlorinated dibenzofurans (PCDF), in addition to the PCDD. An updated review on the effects of 2,3,7,8-TCDD on immunocompetence is timely from a number of perspectives. First, effects on immune function have been demonstrated to be among the earliest and most sensitive indicators of 2,3,7,8-TCDD-induced toxicity. Second, recent evidence indicates that exposure to 2,3,7,8-TCDD causes changes in innate immunity in addition to the changes in acquired immunity (i.e., which include effects on both cell-mediated and humoral immunity) previously shown to be associated with this chemical. Third, effects on immune function are almost universally observed among the animal species in which it has been evaluated, including some non-human primates. Fourth, effects of 2,3,7,8-TCDD on specific indicators of immune function have been correlated with changes in host resistance capabilities, which are often considered to be more holistic indicators of immunocompetence. Fifth, there are several reports which describe possible effects of 2,3,7,8-TCDD and related compounds (i.e., primarily PBB and PCB) on immune function in humans. It is important to emphasize at the onset that these studies have triggered much controversy, both political and scientific. However, it is equally important to speculate that at least part of the controversy associated with man's sensitivity to the immunological effects of 2,3,7,8-TCDD may be that the most appropriate approaches have heretofore not been applied. This possibility is discussed further in this review.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of human cytotoxic lymphocyte responses. II. Suppression by a soluble factor produced by primed lymphocytes

A soluble supernatant factor is elaborated from in vitro primed human allogeneic lymphocytes which suppresses the development of alloreactive cytotoxic lymphocytes (CTL). In contrast, supernatants obtained from primary mixed lymphocyte cultures (MLC) and primed autologous cultures were unable to suppress CTL activation, indicating that antigen restimulation was required to elicit the factor. The suppressor factor (SF) functioned in a dose-dependent manner. When the SF was added 24 or 48 hr after MLC initiation it was ineffective. However, adding the SF at culture initiation significantly reduced CTL activity, suggesting that suppression occurs either during antigen recognition or early in the CTL differentiation pathway. The SF did not function by altering the kinetics of the CTL response. Preincubation experiments showed that the SF operates by partially inactivating both MLC responder and stimulator cell populations.

Behaviour of human immunoregulatory cells in culture. I. Variables requiring consideration for clinical studies

The suppressor function of lymphocytes stimulated with concanavalin A (Con A) provides a potential method for examining disorders of immunoregulation. Clinical application, however, requires definition of the culture conditions that influence the expression of normal suppressor cell activity. In the present studies culture conditions were modified until a sensitive assay for non-specific suppressor cell function was reproducible utilizing the response to varying doses of phytohaemagglutinin (PHA) as an indicator system. Practical conclusions included (1) that sensitivity was not lost if the suppressor cells and responder cells were allogenic; (2) that fresh responder cells were as sensitive as precultured responder cells; (3) that a wide range of Con A concentrations could induce suppressor activity; and (4) that the sensitivity of the assay was much enhanced by using suboptimal mitogen doses of PHA. Twelve percent of normal subjects gave false negative results but these could be avoided by studying cells at more than one time point after stimulation with Con A. Cells resting in culture for 7 days could be induced to suppress after stimulation with Con A and these suppressor cells were very sensitive to pharmacological doses of dexamethasone. Studies utilizing different times of cell pre-incubation before Con A stimulation and different periods of exposure to Con A revealed fluctuation in the induction of suppression that may represent alternating periods of suppression and amplifying activity among stimulated cells in vitro. Such variations will need to be taken into account in the application of this type of assay to clinical studies seeking disordered immunoregulation.

Chick embryo pancreatic transplants reverse experimental diabetes of rats

The effectiveness of xenogeneic embryonic tissue in the treatment of experimental diabetes has been investigated in rats. The splenic lobes (80) of 15- to 18-d-old chick embryos, composed almost exclusively of endocrine tissue, were implanted directly into the hepatic parenchyma of the rat recipient. The biochemical and metabolic changes in the recipients suggest that embryonic transplants of 15-d-old chick pancreases were able to significantly improve, for a prolonged period of time (18 mo), the diabetic state of nonimmunosuppressed rats. None of the recipients of 18-d-old embryos splenic lobes exhibited a long-term improvement of the diabetic state after transplantation. The complete destruction of the pancreatic B cells of the recipients was assessed by: (a) immunocytochemical investigations of the recipient's pancreas, (b) measurement of insulin in the liver and pancreas of the recipients and (c) in situ vascular perfusion of their pancreas submitted to high glucose challenge. The results suggest that pancreatic tissue of the 15-d-old embryos is immunologically immature lacking one or several lymphocyte subsets implicated in the afferent lood of "non-self" recognition.

Help and suppression by lymphoid cells as a function of cellular concentration

The phytohemagglutinin-stimulated uptake of [3H]thymidine in mixtures of human lymphocytes from the same source was shown to depend on the cell concentration in vitro as well as on the period of cultivation. "Helper" and "suppressor" effects were obtained by varying the concentration of cells and the periods of cultivation. The possibility that helper and suppressor subpopulations were responsible was avoided by mixing lymphoid cell line cells with others of the same monoclonal origin. Even under these conditions, both the direction and the extent of activity depended on the same two variables. This weakens the case for postulating the existence of distinct subpopulations of lymphocytes with helper or suppressor properties. This case was based on the use of damaging treatments believed to separate cell populations which were then found to differ in their helper and suppressor properties. We propose instead that the effect of such treatments is mediated through changes in the concentrations of interacting cells. Our data make it clear that the function of lymphoid cells ascertained in one set of conditions need not apply within a different cellular environment.

Characterization of rat spleen-cell populations. I. Cell interactions in the regulation of in vitro response to concanavalin A

Spleen cells from BN rats were separated in a discontinuous density gradient. Cells from different fractions were shown to be functionally diverse, light cells enhancing DNA synthesis and cell division of the dense cell fractions, while dense cells suppressed DNA synthesis and cell division of light cells. Both these effects were also present in the absence of cell stimulation, were proportional to the number of modulating cells added to the cultures, and totally independent of the magnitude of response of controls. In Con A-stimulated cultures, mitogen dose also influenced the intensity of help and suppression. Both these effects are blocked by cell treatment with cycloheximide and can be mediated by cell supernatants. A T cell seems to be responsible for both helper and suppressor effects.

Restimulation of PPD-stimulated lymphocytes: decreased responsiveness of prestimulated cells to a second challenge with PPD and PHA

Lymphocytes stimulated with purified protein derivative (PPD) were inhibited in their response to a second stimulation with PPD or phytohaemagglutinin (PHA). The degree of inhibition was related to the PPD concentration during prestimulation, the dose-response curve for inhibition resembling very much that of stimulation. The decreased reactivity was neither due to a toxic effect of PPD nor to altered proliferation kinetics of the prestimulated cells. Lymphocytes preincubated for 6 h or 16 days with PPD were equally refractory, and the non-reactivity persisted even if the cells were incubated without stimulant for 1 week or more. The prestimulated cells were able to suppress the PHA stimulation of fresh lymphocytes. These results indicate that the decreased reactivity of the prestimulated lymphocytes is due to the action of suppressor lymphocytes, generated during the primary stimulation.

Regulation of immune response to SRBC: suppressor cell activity induced by soluble fraction of antigen

Water soluble fraction (SF) of SRBC was obtained by hypotonic lysis and ultracentrifugation. SF was found to induce very weak SRBC-specific antibody response in mice. Pretreatment with SF accelerated direct PFC response to SRBC and accelerated and suppressed indirect PFC response. Spleen cells from mice treated with SF exhibited enhanced response to SRBC after transfer in irradiated recipients. The transfer of spleen cells from mice treated with SF to normal non-irradiated mice markedly suppressed the recipients' PFC responses to SRBC. The observed suppressive effect is interpreted as a consequence of suppressor cell activity.

Self and non-sense: an organism-centered approach to immunology

This paper provides a conceptual framework to accommodate important recent developments in immunology (genetic determination, cellular interactions, suppression). The basic idea is to look at the immune system as a closed network of interactions which self-determines its ongoing pattern of stability and its capacities of interaction with its environment. Thus, all immune events are understood as a form of self-recognition, and whatever falls outside this domain, shaped by genetics and ontogeny, is simply nonsensical. This paradigm, stemming from the ideas of Jerne, represents almost a logical inversion of the Burnetian idea of self-discrimination. A detailed discussion of the immunological evidence that substantiates this view is presented, together with some new concepts (eigenbehavior, cognitive domains). Although the paper is addressed to biologists and immunologists, we make extensive use of system-theoretic notions in a non-mathematical form (recursion, nets and trees, self-organization).

Modulatory effects on immunoglobulin synthesis and secretion by lymphocytes from immunodeficient patients

Incubation of peripheral lymphocytes (PBL) from normal donors with pokeweek mitogen (PWM) induced terminal differentiation by B lymphocytes to immunoglobulin (Ig) synthesizing and secreting plasma cells. B cells from hypogammaglobulinemic patients with different primary immunodeficiencies failed to undergo functional differentiation after similar treatment with PWM. Co-cultures of BL from normal donors and hypogammaglobulinemic patients often resulted in deviations, both positive and negative, from expected levels of PWM-stimulated intracellular Ig biosynthesis. Suppression of B-cell differentiation was manifested by PBL from patients with several different primary immunodeficiencies, including infantile sex-linked agammaglobulinemia. Immunoregulatory activities were noted to vary with the normal donor used in co-culture experiments and with time. Cell populations that were active in influencing B-cell differentiation to functional plasma cells did not have an appreciable modulatory effect on T-lymphocyte responses to mitogens. These observations may provide a functional subclassifications for immunoregulatory cells in man.

Experimental conditions for obtaining suppressor and helper effects on the primary in vitro immune response by lymphocytes activated by polyclonal T-cell activators

The effect of the polyclonal T-cell activators (PTA) Con A and PHA on the specific immune response to sheep red blood cells (SRC) was studied. Addition of PTA either enhanced or suppressed the anti-SRC response, and two variables were found to affect the results: time of addition of the PTA and the strength of the response in control cultures not given PTA. If the response was high, even suboptimal PTA concentrations induced suppressive effects, but if the control response was low, due to deficient batches of sera or because of the absence of serum, the addition of PTA increased the response or restored it to normal levels. Suppression could be obtained if the PTA were added before or at the same time as the antigen and required high (optimal) PTA concentrations. If addition was delayed for 12-24 h the suppressive effects disappeared and previously suppressive concentrations of the PTA now caused an enhanced response. Analogous results were obtained if preactivated lymphocytes were added to the cultures instead of soluble PTA. Neither Con A, PHA, or lymphocytes preactivated by these PTA suppressed the polyclonal response induced by LPS or PPD. Irrespective of the time of addition and the culture conditions, enhancement of the anti-SRC response occurred at lower PTA concentrations than suppression. It was concluded that suppressor T cells, if they exist, do not act on B cells, but rather on helper cells needed for induction of thymus-dependent responses. The findings in this system are not compatible with the existence of a specific subset of suppressor T cells, but rather with the notion that suppression is caused by too much help.

Selective activation of human suppressor cells by a nonproliferative stimulus

The eliciting of suppressor cell activity by heat-treated stimulating cells demonstrates that suppression can be induced by an antigenic but non-effective mixed lymphocyte culture (MLC) stimulus in vitro. Simultaneous or prior MLC or cytotoxic T lymphocyte activity is not required for alloantigen-induced suppressor cell activation.

Serum modulation of in vitro cellular immune reactivity to Epstein-Barr virus-associated antigen

The reactivity of peripheral blood leukocytes to Epstein-Barr virus-associated antigen was assessed employing two in vitro tests, leukocyte adherence inhibition (LAI) and leukocyte migration inhibition (LMI). In both tests, autologous serum from some normal subjects was shown to confer strong reactivity on weak or non-responder cells. Reactivity to purified protein derivative of tuberculin (PPD) assessed in parallel was shown to be unaffected by autologous serum. Employing the LAI system, variations in the effects of autologous serum samples collected on consecutive days was shown to be dependent on the reactivity of the leukocytes themselves, rather than changes in the activity or concentration of factors present in the serum.

The role of receptors for T cell products in antibody formation

Immunocompetent cell interactions are achieved via direct contact between functionally different cell types or via interactions between soluble factors elaborated by regulatory T cells and specific receptors on responding cells for the T cell factors. In either case, there exist certain restrictions with respect to the effective interactions, which depend on the state of differentiation and genetic background of the responding cell type. Such restrictions are considered to be mainly determined by the development and nature of the receptor site on responding cell types for different T cell factors, which is now refered to the "acceptor" for the T cell factors. The presence of such acceptor sites on different populations of both T and B cells has been demonstrated in various experimental systems, and they are now considered to be the site by which responding cells receive appropriate signal for destination of their further differentiation. We have tried to review the nature and possible role of acceptor sites on both B and T cells for different T cell factors with respect to the induction and regulation of immune responses. A special emphasis was put on the genetic nature of the acceptor site. The observed genetic restrictions in the acceptance of T cell factors by responding cells suggest that such restrictions are needed for meaningful and unmistakable communications between funcionally different immunocometent cells. Furthermore, the presence or absence of acceptor sites for certain T cell factors is supposed to be a very important factor for determination of the immune responsiveness of animals against certain antigens, and thus in some cases the Ir gene effect may predominantly affect the expression of acceptor site. Possible implications of acceptor site in the regulation of antibody response and in the network of immunocompetent cell interactions are discussed.