Morphology and microfilament organization in human blood lymphocytes: Effects of substratum and mitogen exposure

During culture in serum-containing medium normal human blood lymphocytes, depleted of phagocytic and adherent cells, do not attach to adhesive surfaces. Concanavalin A (ConA) or phytohemagglutinin (PHA) in appropriate concentrations mediate adhesion of these lymphocytes to tissue culture plastic or glass. This process consists of two phases. 1. 1. The mitogen-mediated contact with a surface induces an almost instantaneous alteration of cell shape and a simultaneous redistribution of actin in the majority of the cells. 2. 2. The initial morphological changes are accompanied by an accumulation of actin-containing material in prominent peripheral cytoplasmic outgrowths formed by the spread cells. The contact-induced spreading and rearrangement of actin are inhibited by cytochalasin B (CB) but not by colchicine or vinblastine. The distribution of detectable actin in spread lymphocytes is similar to the distribution of footprints of actin after detachment of spread cells suggesting that actin is involved in the attachment of lymphocytes to substratum. In contrast to lymphocytes on glass or tissue culture plastic which show morphological changes and redistribution of actin cells cultured with ConA on non-adhesive surfaces of bacterial plastic or poly-2-hydroxy-methacrylate do not exhibit any morphological alterations and no rearrangement of actin. The present approach enables visualization of cytoskeletal structures in lymphocytes to an extent which is not possible using conventional methods with the cells in suspension. The results indicate that contact is a regulator of lymphocyte shape and that actin-containing structures mediate and maintain contact-induced changes of lymphocyte morphology.