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A. ANTIBODY RESPONSES OF HUMAN TONSILLAR LYMPHOCYTES. 1 Human tonsillar lymphocytes were stimulated with pokeweed mitogen in vitro. A large number of cells developed which secreted antibody specific for sheep erythrocytes. The largest number of antibody-forming cells was produced on days 4 or 5, when optimal cell concentrations were used. Responses specific for bovine and horse erythrocytes were much smaller than those specific for sheep erythrocytes. 2 Antibody responses were studied using a culture system which permits the segregation of individual clones of antibody-forming cells. As the number of cells in each culture was increased, the efficiency with which clones were produced and the mean clone size also increased. Cell dose-response data suggest that precursors of clones detected on day 4 are less dependent on cell co-operation than those giving rise to clones detected on day 5. The frequency of antibody-forming cell precursors at the peak of the response was estimated at 1.2 to 3.8 x 10-5. 3 The physical properties of antibody-forming cell precursors were investigated. When fractionated by sedimentation velocity, precursors appeared to be enriched in fractions of cells with a larger volume than the majority of lymphocytes. Precursors were heterogeneous when fractionated on the basis of their buoyant density. Little precursor activity was detected in cells with a density of greater than 1.075 g/ml. Cells able to generate antibody-forming cells were most enriched in fractions with a density of about 1.065g/ml. Cells which suppress responses are also found in fractions of this density. 4 Hydrocortisone succinate at 1μg/ml (2μM)enhanced the production of antibody-forming cells in many experiments. Hydrocortisone had to be present from the time that cultures were initiated in order to exert this effect. The effect of hydrocortisone upon cells which had been fractionated on the basis of their buoyant density was examined. It was able to potentiate the responses of two medium density fractions only, and actually suppressed the responses of high density cells. 5 Hydrocortisone enhanced an antibody response stimulated by sheep erythrocytes in a similar way as it enhanced PWM-stimulated responses. The addition of sheep erythrocytes to PWM-stimulated cultures enhanced PFC responses only in the presence of the hormone. These data are interpreted as showing that suppressor cell activity is selectively inhibited by hydrocortisone. B. THE EFFECT OF IN VIVO PLASMACYTOMA GROWTH ON ANTIBODY RESPONSES OF MURINE SPLEEN CELLS IN VITRO. Spleen cells from normal and plasmacytoma-bearing mice were cultured and their antibody responses compared. In those instances where the production of antibody-forming cells was dependent upon helper T cells, it was found that the responses of cells from tumour-bearing mice were enhanced relative to controls. Thymus-independent responses were not enhanced. Evidence is presented that the nature of the effect of tumour growth upon antibody responsiveness is related to the culture system used. |
