Robert R. Rich

Role of calcium and magnesium and of cytochalasin-sensitive processes in lectin-stimulated lymphocyte activation

Abstract We have investigated possible interactions of divalent-cation-requiring processes and cytochalasin-sensitive processes in the early events of lymphocyte activation. In lectin-stimulated responses, Ca and Mg were synergistic in support of protein and DNA synthesis, as expressed in the increased requirement for one ion under conditions of depletion of the other. Experiments evaluating the temporal relationships between cytochalasin sensitivity and requirements for Ca and Mg demonstrated that both cations were required before or during the early cytochalasin B-sensitive events. Furthermore, we observed that Ca and Mg and cytochalasin B-sensitive processes were required for lectin-dependent commitment to DNA synthesis. Additional studies comparing the relative potencies of cytochalasin E, D, and B suggested that the probable target for cytochalasins in the inhibition of commitment was a motility-related process. These data demonstrate an early period of activation which can be characterized by its requirement for divalent cations and its sensitivity to cytochalasins.

Recognition of Hapten-Modified Cells In Vitro by Human T Lymphocytes

Clearer definition of the recognitive structures of human T lymphocytes for antigens will be required to elucidate the molecular basis of diseases and immunological responses induced or regulated by normal or abnormal T-cell function. For this purpose we have investigated the cellular requirements for immune responses in vitro to trinitrophenyl-conjugated peripheral blood mononuclear cells. The responding cell was characterized as a T cell on the basis of rosetting with sheep erythrocytes. T-cell recognition of hapten in proliferative responses depended upon presentation of antigen in an appropriate stimulator-cell context. Neither autologous hapten-modified erythrocytes nor T cells restimulated responses of in vitro-primed lymphocytes. Moreover, hapten-conjugated non-T cells were more effective than modified unfractionated cells in restimulating proliferative responses. Both macrophages and non-T lymphocytes effectively restimulated hapten-conjugate responses.Cell-mixing experiments indicated that the failure of haptenated T cells to stimulate proliferative responses was not because of a lack of fresh macrophages; these experiments suggested instead that T cells do not express appropriate structures necessary to present haptenic determinants in an immunogenic form. Hapten-modified T cells, however, were capable of inducing primed lymphocytes to become efficient cytotoxic effector cells, indicating that T-cell recognitive units for stimulation of proliferative and cytotoxic responses are different. These data support the concept that for induction of proliferative responses, human T cells recognize conventional antigens in association with HLA-D-region-encoded Ia-like molecules.

SUPPRESSION OF IMMUNE RESPONSES BY PRODUCTS OF ACTIVATED T CELLS

Publisher Summary This chapter focuses on the characteristics of several selected T-cell factors that suppress immune responses. These factors, although apparently distinct in methods of production, biochemical characteristics, and biological activities, share interesting common properties. In a study described in the chapter, the soluble immune response suppressor (SIRS) was secreted into culture supernates by mouse T cells incubated 6–48 h with mitogenic concentrations of ConA. SIRS-containing supernates, when assayed in a final concentration of 1:40 to 1:100, are not cytotoxic but, if added to cultures at initiation, suppress both IgM and IgG PFC responses to a large extent. The SIRS has little effect when added 24 h after culture initiation, and when added at 48 h or later, it does not significantly alter day 5 PFC responses. Physicochemical studies of SIRS have revealed striking similarities to murine migration inhibitory factor.

Divalent cations and cytochalasin B-sensitive processes in activation, synthesis, and release of mixed leukocyte reaction suppressor factor

Abstract We have examined the possible rotes of divalent cations and of cytochalasin B-sensitive processes in the production of mixed leukocyte reaction suppressor factor (MLR-TsF). Ca but not Mg was strictly required for MLR-TsF production. A requirement for Mg could be demonstrated only under conditions of Ca depletion, suggesting an intimate linkage in divalent cation requirements. Ca was required for synthesis as well as release of the suppressor factor. Cytochalasin B inhibited MLR-TsF production only when present during the first 4 hr of culture; such inhibition was reversible with incubations of up to 16 hr. This indicated that cytochalasin B inhibited early events of activation, rather than synthesis or release of MLR-TsF. It was found that both Ca and Mg were required either before or during the cytochalasin-sensitive steps in the activation sequence. The relationship of cytochalasin B-sensitive events in early activation to the antigenic stimulus per se was established by limited exposure of suppressor cells to allogeneic stimulators fixed to poly- l -lysine (PLL)-coated plates. Maximal stimulation was observed with a 4-hr exposure, and this antigen-dependent commitment was cytochalasin B sensitive.