Changes in the microtubular skeleton of human lymphocytes produced by immunosuppressive substances

The technique of immunofluorescent visualization of the microtubular skeleton of human lymphocytes isolated from the peripheral blood of healthy donors and immobilized on Concanavalin A--precoated slides was used. These lymphocyte monolayers are suitable for extraction and employment of indirect immunofluorescence. Using a monoclonal antitubulin antibody, one can visualize the MT apparatus of control human lymphocytes as an organizing centre with attached beamlike structures. Lymphocytes treated with ATG or monoclonal OKT 3 antibody in vitro manifest changes in the shape of cells, inhibition of the blast-like cell formation, and an atypical MT system: disturbance or even disappearance of the beamlike structure, formation of bundles and "caps" resulting, in some cases, in shedding of a part of cytoplasm. Rabbit ATG binds to all the cells of the monolayer, and can be shown even after cell extraction. Control experiments with nonspecific rabbit or murine IgG did not induce any of the above changes. Reorganization of the MT apparatus of human lymphocytes affected by ATG or OKT 3 in vitro can be explained either by a direct association of antigenic determinant with MT, or by the persistence or/and internalization and further processing of immune complexes of antigenic membrane determinants with specific antibodies.