Electron microscopic analysis of the modulation of lymphocyte receptor mobility

Abstract

The topographic distribution of ferritin-labelled concanavalin A (FT-ConA) bound to the surface membrane of mouse lymphocytes has been analysed by examining ultrathin sections and ghost membranes in the electron microscope. Binding of FT-ConA to lymphocytes at 37 °C did not induce redistribution of ConA receptors at any dose of the labelled lectin. In contrast, in cells treated with colchicine, FT-ConA induced both patch and cap formation. These findings suggest that the modulation of receptor mobility by colchicine occurs at the level of individual receptors. Ultrastructural observations revealed both microtubules and microfilaments in lymphocytes consistent with the suggestion that these cellular structures may be involved in the control of receptor mobility. Analyses using freeze-fracture methods indicated that the distribution of intramembranous particles is not correlated with either the movement of surface receptors or the modulation events. An hypothesis on the modulation of surface receptors by cytoplasmic structures is proposed on the basis of these and previous observations.