Ligand-independent cap formation: redistribution of surface receptors on mouse lymphocytes and thymocytes in hypertonic medium.

Most of the mobile receptors on mouse lymphocytes and thymocytes, including immunoglobulins, H-2 antigens, Thy-1.2 antigens, some concanavalin A receptors, and some antigenic determinants detected by anti-thymocyte serum, were redistributed into caps when the cells were incubated in hypertonic medium (about 600 mOsM) in the absence of ligands. The caps reverted to the original distributions if the cells were transferred again to isotonic medium. The viability of the cells was not decreased after incubation in the hypertonic medium. Ligand-independent cap formation appeared to depend upon cellular metabolism. Different species of receptors appeared to move with different mobilities during the process of ligand-independent cap formation. Most microvilli on cells showing caps in hypertonic medium were associated with the regions of the caps. These results suggest that free receptors can be induced to form caps if the receptors are allowed to interact with the machinery of cap formation under special conditions.