[Regulation mechanisms of the activity of T lymphocytes. Applications to infective and tumoral pathology. I. Delayed hypersensitivity and humoral response (author's transl)].

Delayed-type hypersensitivity (DTH) develops in the absence of an adjuvant when mice are injected with an apropriate dose of Sheep Red Blood Cells (SRBC). Increasing the dose of SRBC reduces and eventually abolished all evidence of DTH and no further sensitisation can be achieved even with the optimal subcutaneously injected dose, except in splenectomised mice in whom the development of DTH is not suppressed, even by massive doses of SRBC. This is also the case in mice treated with cyclophosphamide (CY) which suppresses selectively the antibody response. Hence the suppression of T cell activity measured as DTH cannot be due to antigen as such. The serum of blocked animals partially inhibits the induction and expression of DTH, and its blocking activity increase substantially after partial absorption. Absorbed serum did not inhibit in vivo the proliferative response nor the number of plaque forming cells to SRBC in peripheral lymph nodes, it increases the hemagglutinating titer of circulating specific antibody even though DTH is totally suppressed. It seems that the products of the interaction between antigens and antibodies block the activated T cells which mediate DTH without interfering with helper cells.