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Peripheral blood lymphocytes from MS patients and from healthy control donors were compared for their ability to mediate spontaneous and antibody-dependent cell-mediated cytotoxicity. They were also compared for their ability to respond to infection with various strains of measles and sSPE viruses with interferon production and enhanced NK activity. Neither SLMC nor ADCC against several different target cells was found to be impaired in the MS population. Furthermore, no defect was detected in the response of patients' lymphocytes to virus challenge in vitro in terms of both activation of NK cells and interferon production. Enhanced NK activity was also induced by an exogenous interferon preparation and by Poly I:C to the same extent in patients and controls.

An increase in the percentage of IgG bearing peripheral blood lymphocytes is observed in aged subjects as compared with young ones. Such a finding is probably due to the presence, in 'aged' sera, of a higher concentration of immune complexes, bound to lymphocytes through their Fc or Complement receptors.

In human one-way mixed lymphocyte reactions we have observed an increase in the percentage of sIgD bearing lymphocytes, detected by direct membrane immunofluorescent staining. This increase does not seem to be attributable either to the synthesis of sIgD receptor molecules by previously negative T or null cells or to a non specific stimulation of B cells by a factor released in the course of the MLR.

The production of interferon (IF) by human and mouse lymphocytes sensitized to alloantigens in mixed lymphocyte cultures (MLC) was analyzed. During primary MLC, IF appeared in the culture fluid on day 2 and was maximal on day 5. Based on several biologic criteria, the IF produced is of the "immune" type. When lymphocytes sensitized to alloantigens were reestimulated in vitro, IF was produced within a few hours of culture. In all stimulated cultures, cell proliferation was observed in spite of the high concentrations of IF. The IF-producing cells in human MLC were identified as T lymphocytes lacking the receptor for the Fc fragment of IgG molecules (Fc gamma R(-)). Human MLC supernatants containing immune type IF mediate the enhancement of natural killer (NK) cell activity and protect NK target cells from lysis.

We present evidence that human peripheral blood lymphocytes, free of contaminating monocytes, rapidly produce high levels of tumor necrosis factor (TNF) when stimulated with phorbol diester and calcium ionophore, and lower but significant levels of TNF when stimulated with mitogens. These two types of inducers act preferentially on T cells, both CD4+ and CD8+. NK cells produce TNF only when stimulated with phorbol diester and calcium ionophore, and they do so at a much lower level than T cells. The procedures used in the purification of lymphocytes and the differential ability to respond to various inducers allow us to exclude that monocytes or basophils contaminating the lymphocyte preparation participate in the production of TNF. In particular, LPS, a potent inducer of TNF production from monocytes, is unable to induce significant levels of TNF in the lymphocyte preparations. The TNF produced by lymphocytes has antigenic, physicochemical, and biochemical characteristics identical to those of the TNF produced by myeloid cell lines or monocytes upon stimulation with LPS. LT is also produced by lymphocyte preparations. Production of TNF and LT proteins in response to the different inducers is paralleled by accumulation of cytoplasmic TNF and LT mRNA. Both at mRNA and at protein levels, stimulation of T lymphocytes with phorbol diester and calcium ionophore preferentially induces TNF, whereas mitogen stimulation preferentially induces LT. Our data suggest that the TNF and LT genes, two closely linked genes encoding two partially homologous proteins with almost identical biological functions, are independently regulated in lymphocytes.

CTL and NK cells resist self-mediated killing and lysis by their own pore-forming protein (PFP; perforin). Perforin, like C, lyses RBC. Efficient C-mediated lysis of RBC occurs when both C and RBC are from different species (homologous species restriction). A protective surface protein (C8-binding protein, homologous restriction factor) has been reported to mediate both homologous species restriction in C-dependent cytolysis and protection of some target cells against perforin-induced lysis. We show here that perforin, unlike C, lyses target cells across a variety of species, including the homologous one, while the same target cell populations resist the attack by homologous C. Perforin-containing extracts of CTL and LAK/NK cells from three species (rat, mouse, and human) and purified mouse perforin were tested against RBC from 10 different species, several nucleated target cell lines, and one primary cell population (thymocytes). While resisting lysis by homologous C, most of these cell types were lysed effectively by perforin without any homologous restriction pattern. CTL and NK cells, like other nucleated targets, are resistant to lysis by homologous but not heterologous C; however, these cell types are resistant to both homologous and heterologous perforin. Together, our results suggest that the protective mechanisms associated with C- and perforin-mediated lysis are distinct.

Human monoclonal IgM antibodies present in the blood of some patients with peripheral neuropathy and murine hybrid IgM antibodies C5 and C6, raised against myelin-associated glycoprotein, and HNK-1, raised against the human T cell line HSB-2, all bind to the carbohydrate moiety of myelin-associated glycoprotein. The relative avidity of the monoclonal antibodies was HNK-1 greater than C5/C6 much greater than human IgM, as determined in a competitive binding radioimmunoassay. HNK-1 bound myelin equally well at incubation temperatures between 4 degrees C and 37 degrees C; the human antibodies bound significantly only at 4 degrees C; and C6 bound best at 4 degrees C, less strongly at 20 degrees C and did not bind at 37 degrees C. All of the antibodies bound to a band corresponding to myelin-associated glycoprotein on immunoblots of human CNS myelin proteins in addition to several other antigens. Flow cytometric studies revealed that the murine but not the human antibodies bind to peripheral blood lymphocytes. Taken together, these data suggest that the antibodies probably recognize the same epitope but bind with different avidity.