[Lymphocytes. Roles in cellular immunity and humoral immunity]

The lymphocytes are now considered as ubiquitous cells which play a role in delayed hypersensitivity, the rejection of grafts and antibody synthesis. The lymphocytes are essential in the immune process, for they may both recognise the antibody and initiate the response. They act either by themselves or after differentiation into specialised cells and, usually, in coordination with other cells with phagocytic functions. After briefly recalling the morphology, localisation, circulation, sites of production and heterogeneity of the lymphocytes, the authors discuss their function, describe lymphocytic transformation, and the role of T lymphocytes in delayed hypersensitivity, in the rejection of grafts and the direct cytotoxic effect. Antibody synthesis with B lymphocytes and the intervention of mononucleated cells with phagocytic activity, the cooperation of T lymphocytes are developed. The exploration of lymphocytic functions includes the recognition of an antigen by the lymphocyte, fixation of marked antigens, rosette formation, the demonstration of delayed hypersensitivity (inhibition of macrophage migration, cytotoxicity, skin tests), the estimation of antibodies and measurement of lymphocyte transformation. Certain factors, due to antigen-host reaction, regulate the lymphocytic immune reaction. One may experimentally intervene by immunostimulation and immunosuppression.