Antigenic competition in vitro between heterologous erythrocytes

Differential effects of immunisation with mycobacterial 65 kD heat shock protein on two models of autoimmunity

The effects of preimmunisation with the 65 kD mycobacterial heat shock protein (hsp65) on 2 murine models of autoimmunity were compared. Experimental autoimmune haemolytic anaemia (AIHA) can be provoked in mice by repeated injection with rat red blood cells (RBC). In this model, preimmunisation with hsp65 10 days before induction of disease resulted in a partial, but significant, reduction in RBC-bound autoantibody levels measured by Coombs' test. However, preimmunisation with human IgG (hIgG) was associated with a similar suppressive effect. Administration of neither hsp65 nor hIgG affected the direct or indirect anti-rat agglutinin titres of mice subsequently injected with rat RBC. Injection of hsp65 or hIgG prior to induction of AIHA elicited the production of IgG antibodies against the respective immunogen, as judged by enzyme-linked immunosorbent assays. In contrast to the results in experimental AIHA, pristane-induced arthritis (PIA) was effectively prevented by preimmunisation with hsp65, but not with hIgG. It is considered that, whilst hsp65 injection may slightly reduce subsequent anti-RBC autoantibody production in AIHA by antigenic competition, such a mechanism cannot account for the substantial protection against PIA afforded by hsp65 preimmunisation. We suggest that the high, sustained production of anti-hsp65 antibodies observed in mice given hsp65 and pristane may play a role in specifically suppressing arthritogenic immune responses in PIA.

Suppressor function of peripheral blood mononuclear cells in normal individuals and in patients with systemic lupus erythematosus

Normal peripheral blood mononuclear cells demonstrated increased DNA synthesis and secretion of newly synthesized protein when suboptimal concentrations of Concanavalin A (Con A) were added to the cultures after 24-h incubation in vitro. Cells stimulated by Con A, 1 mug/ml, after 24-h incubation demonstrated 3.0 times more tritiated thymidine incorporation, and 4.4 times more 14C-amino acid incorporation into newly synthesized secreted protein, than cells stimulated at 0 h (P less than 0.001). The acquisition of increased responsiveness was not abrogated by washing and resuspending the cells in fresh medium. Since the increased responsiveness could be inhibited by the addition to the cultures of small numbers of cells previously activated by Con A it is suggested that the enhanced reactivity acquired in culture represents the loss of a subpopulation of suppressor cells that modulate the T-lymphocyte response. Cells from nine patients with active, untreated systemic lupus erythematosus demonstrated normal responses to optimal concentrations of Con A added at 0 h, but an impaired response to Con A, 1 mug/ml. When these cells were incubated for 24 h, a significant increased response to Con A was not observed. This observation suggests that patients with active SLE lack circulating suppressor cells. When seven SLE patients were again studied after corticosteroid therapy had led to clinical improvement, the response to Con A, 1 mug/ml, added after 24-h incubation was similar to that observed in normal controls, suggesting that suppressor function in SLE returns as disease activity declines.

Reversal of immunosuppression induced by murine leukemia viruses

BALB/c mice infected with Rowson-Parr virus, a lymphatic leukemia virus isolated from the Friend complex, undergo a rapid depression of antibody response. Spleen cells from these mice in culture show a similar deficit in the response to stimulation with sheep red cells and inhibit the reactivity of normal splenocytes. In an attempt to reverse this immunosuppression, near normal responses were obtained in vitro from infected splenocytes by increasing antigen dose, by adding E. coli lipopolysaccharide, or, more effectively, by cocultivating with small numbers of unfractionated or T cell-depleted peritoneal exudate cells (PC), whereas other manipulations proved ineffective. PC did not prevent the inhibition of normal splenocytes by infected spleen cells, but exhibited substantial restorative activity in vivo. In similar experiments, the immunosuppression exerted by the entire Friend complex could be reversed by PC in vitro but not in vivo. These results indicate that a functional deficit of macrophages may be partially responsible for the immunological impairment induced by leukemia viruses and suggest rational approaches to evaluate the relevance of this impairment to oncogenesis.

A theory of regulation and self-nonself discrimination in an immune network

A mechanism is suggested for the regulation of the immune response that involves antigen-binding and anti-idiotypic lymphocytes. The cross-linking of receptors is postulated to be a general mechanism for triggering T cells, B cells and cytotoxic effector cells (e.g. macrophages). A key role in regulation is ascribed to antigen-specific T cell-dependent factors, which are assumed to be able to block the receptors of both T cells and B cells of the anti-idiotypic specificities. The simple postulates of the model lead to feasible mechanisms for the helper, suppressor and killer roles of T cells, cellular and humoral immune responses, low zone tolerance and the tolerogenic effects of monomers, immune memory, antigenic competition, the abrogation of tolerance with cross-reacting antigens, the usefulness of the switch from IgM to IgG, and self-tolerance to both serum antigens and cell surface antigens. Biological roles are suggested for one of the Ia antigens and beta 2-microglobulin. The theory leads to a number of predictions, which can be tested experimentally. A simple mathematical model is included, which provides an indication of how the theory may be further developed on a quantitative basis.

Heterogeneity of the effector cells in the cytotoxic reaction against allogeneic lymphoma cells

The cytotoxic effect of spleen cells from H-2 allogeneic mice was tested in vitro against an A strain leukemia (YAC) labeled with [(125)I]iododeoxyuridine. After the mice were primed with tumor cells, significant and specific H-2 immunity was detected on day 3 and peak cytotoxicity was observed between 7 and 14 days after priming. Two effector cells appear to be involved in the host response, because spleens taken from mice soon after priming were not sensitive to antitheta sera and complement while those taken during the peak stages of the response showed a marked reduction in cytotoxicity after treatment. Macrophages were not involved, since removal of these cells by the carbonyl iron method did not result in any reduction in cytotoxicity. Immune serum that was capable of inducing cell-mediated cytotoxicity in normal spleen cell populations also augmented cytotoxicity of spleen cells taken from mice primed 3 days previously. However, when spleen cells were taken from mice during the peak phase of the immune response, the same serum at the same dilutions inhibited the preexisting cytotoxicity. A difference was also detected in the killing efficiencies between early and late immune cells.