OKT3-activated locomotion of human blood lymphocytes: a phenomenon requiring contact of T cells with Fc receptor-bearing cells.

The OKT3 antibody activates locomotion of human blood T lymphocytes as measured by polarization assays and invasion of collagen gels. The proportion of motile cells increases during a period of 24-48 hr of culture, even following only a brief initial contact with OKT3. The motile cells are the growing population. Locomotion activation is cell-density dependent. Studies with surface-bound mitogens, namely substratum-bound OKT3 and Con A-Sepharose, showed that only lymphocytes in direct contact with the mitogen acquired locomotor capacity. Those separated from it by a cell-impermeable filter were not activated. The response to OKT3 requires the whole antibody molecule. F(ab')2 fragments were inactive. Intact normal human IgG, but not its F(ab')2 fragments, blocked the response. Removal of RFc gamma + cells from the population by rosetting with IgG-Ab-coated sheep red cells prevented the response. These findings suggest that an RFc gamma + population has to be present for T cells to become activated to locomotion by OKT3, and that the OKT3 antibody links the T cell to an FcR+ cell, cell-to-cell contact being essential for activating the locomotor response.