Effect of antigenic competition on antigen-sensitive cells and on adoptively transferred immunocompetent cells

Immunoregulation in fish II: intermolecular-induced suppression of antibody responses studied by haptenated antigens in atlantic salmon (Salmo salar L)

Here we report evidence for T cell dependent intermolecular-induced suppression of antibody responses in fish, using a panel of T cell dependent (TD) and T cell independent (TI) hapten-carrier antigens. Atlantic salmon were immunized intraperitoneally either with protein antigens: Limulus polyphemus hemocyanin (LPH), chicken gammaglobulin (CGG), A. salmonicida surface A-layer protein (ALPAsal) or lipopolysaccharide (LPS) antigens isolated from A. salmonicida and Escherichia coli. The various antigens were given as a mixture of the native and haptenated (4-hydroxy-3-iodo-5-nitrophenyl-acetic acid, NIP; 2,4,6-trinitrophenyl-acetic acid, TNP; fluorescein-5-iso-thiocyanate, FITC) forms. The salmon immune system responded to the antigen mixtures by eliciting high anti-hapten titers whereas the antibody titers against protein determinants were low (suppress 65-95%) as determined by ELISA. The suppression was induced between haptens (NIP and FITC) and between heterologous antigens (NIP-CGG and LPH) indicating that the mechanisms involved were non-specific. Moreover, suppression was induced by TD antigens only, indicating that the mechanism was T cell dependent. Injection of antigen mixtures containing variable amounts of the competing antigens showed that the kinetics of suppression was dose-ratio and dose dependent. In a time-course study it was found that the suppressed anti-LPH response was unchanged until native LPH was injected almost 2 years after the primary immunization, showing that permanent tolerance had not been induced. Sequential immunization showed that the antibody response was most sensitive to suppression during the initial 10 days after immunization. Moreover, the carrier antigen was also able to induce suppression of hapten epitopes, but only if the anti-carrier response was allowed to develop for 14 days before the hapten-carrier antigen was injected. This shows that AIS in fish is elicited as a result of the immune response to the dominant antigen, and can be induced against either antigens if the temporal order of administration is reversed. A possible model for AIS as a normal immunoregulatory process in fish is proposed and discussed.

A first or dominant immunization. I. Suppression of simultaneous cytolytic T cell responses to unrelated alloantigens

A first or dominant immunization with one antigen markedly inhibited specific cytolytic T lymphocyte (CTL) responses to a second unrelated alloantigen without suppressing antibody responses to other antigens. Suppression was induced rapidly, became systemic, and could be transferred passively with only serum. Suppression did not result from elimination of cells capable of responding to the second antigen. The mechanisms responsible for this "priority of the first response" may be the same that help protect the fetus during pregnancy, promote renal allograft survival after multiple blood transfusions, and prevent effective CTL-mediated immunity to variants of tumor cells or infectious agents that arise during tumor progression or chronic infections.

Immunoregulation by natural killer cells

Polyinosinic-polycytidilic acid (poly (I:C], a synthetic analog of viral double-stranded RNA (dsRNA), activates natural killer (NK) cells and inhibits induction or promotes termination of the primary IgM response in vivo. Suppression of responses was reproduced in vivo by interferons (IFN) which activate NK cells and in vitro by cells enriched for NK cells. The likelihood that NK cells may be involved in the normal regulation of IgM responses is supported by the following observations: immunization itself induces NK activity at times appropriate to account for termination, NK cells activated by immunization suppress in vitro, mice with high NK activity induced by immunization with one antigen have reduced responses to immunization with a second antigen, and mice with induced loss of NK activity fail to down-regulate IgM antibody responses normally.

Mechanism of action of suppressor cells. In vivo concanavalin-A-activated suppressor cells do not directly affect B cells

The addition of a small proportion (10%) of in vivo concanavalin-A (Con-A)-activated spleen cells to normal spleen cell cultures suppressed the primary immune response to sheep erythrocytes (SRBC) but had no effect on the thymus-independent primary immune response to 3,5-dinitro-4-hydroxy-phenacetyl-conjugated lipopolysaccharide. When Con-A-activated cells were added after 24 h, there was no suppression of the anti-SRBC response but rather an enhanced response when few cells were admixed. Con-A-activated cells did not influence activation of normal cells by polyclonal T- and B-cell activators. It is concluded that Con-A-induced suppressor cells do not act on B cells but rather on helper cells (T cells or macrophages) at a very early stage of the immune response to thymus-dependent antigens.

Defects in the immune system of mice infected with lymphocytic choriomeningitis virus

Acute lymphocytic choriomeningitis virus infection of adult mice is associated with general immunosuppression, which develops during the 2nd week of the infection and persists for a period of 2 to 3 months. Studies of some cellular events in the immune system of infected mice brought to light a number of findings which seemed relevant to this immunosuppressive effect. Colony-forming stem cells, which may act as the precursors of the lymphoid cells, were temporarily inhibited during the first period of the infection. Presumably this inhibition also affected the thymus cells, which decreased dramatically at the same time. At a later stage of infection, defects developed within the population of immunocompetent cells, and this was most probably a consequence of the preceding suppression of the precursor cells. The defects in the immunocompetent cells were temporally related to the immunosuppression and seemed to be the ultimate cause of this phenomenon. At all events, antibody-forming cells were not damaged by the virus. In studies of neonatally infected baby mice, it was found that the development of immunological responsiveness was completely abolished for the first 2 weeks of life. It is therefore probable that the generation of immunocompetent cells was also affected in the babies. Evidence was obtained supporting the hypothesis that this effect played an important role for the induction of tolerance to the virus in the neonatally infected mice.

Regulation of lymphocyte responses in vitro. I. Regulatory effect of macrophages and thymus-dependent (T) cells on the response of thymus-independent (B) lymphocytes to endotoxin

DNA synthesis of normal rat spleen cells in response to endotoxin increases markedly if adherent cells are first removed from the cell suspension. Addition of small numbers of purified macrophages to the cultures restores the response to a low level. T-deprived cells show these effects in very much lesser degree. Large numbers of macrophages completely suppress the response of both normal and T-deprived spleen. We conclude that two mechanisms of suppression are at work: a direct effect of macrophages and a macrophage-dependent "suppressor T cell" effect.

Antibody formation: reduced responses after administration of excessive amounts of nonspecific stimulators

Enhancement of antibody formation in vitro and in vivo by poly(A.U), cyclic AMP, dibutyryl cyclic AMP, or any one of these agents in combination with theophylline or caffeine, is usually limited to certain dose ranges. High doses of these nonspecific stimulators can produce less or no enhancement, or may actually inhibit antibody formation. Such dose-response relationships may be pertinent to an understanding of phenomena of specific immunological nonresponsiveness and certain types of antigenic competition.

Antigen competition: a paradox

Immunization of mice with pig erythrocytes caused impairment of the antibody response to subsequent immunization with sheep erythrocytes, a phenomenon called "antigen competition." Paradoxically, spleen cells from mice previously injected with pig erythrocytes produced an increased response when immunized in vitro with sheep erythrocytes. Augmentation of the in vitro response is due to an increase in one of the interacting cell types. "Antigen competition" is not due to competition for cells. Cell transfer experiments provided evidence that "antigen competition" observed in animals is the result of a humoral factor, presumably antibody, present in the animal but eliminated during preparation of cells for culture.