Fluorescence polarization studies and biochemical properties of membranes exfoliated from the cell surface of rabbit thymocytes in situ.

In the course of our work on membrane phenomena related to the differentiation of lymphocytes in the rabbit thymus, we isolated membranous material from the extracellular compartment of this organ. With respect to their ultrastructural appearance, enzyme activity, lipid composition (cholesterol/phospholipid molar ratio, fatty acid composition of total phospholipids, phospholipid composition) and lipid fluidity, these membranes were shown to exhibit characteristics similar to those of purified plasma membranes isolated from disrupted thymocytes. Moreover, their antigenic specificity as determined in a cytotoxicity adsorption test was identical. From our experiments, we hypothesize that the extracellular membrane fragments found in the rabbit thymus are derived mainly from material shed by immature thymocytes.