Preferential distribution of surface immunoglobulins on microvilli

Abstract

MOST lymphocyte surface molecules including surface immunoglobulin (s-Ig) are mobile and essentially randomly dispersed in the plane of the membrane (reviewed in ref. 1). It has been recently shown, however, that a spontaneous non-uniform redistribution of surface molecules such as s-Ig (ref. 2), θ antigens³ and concanavalin A receptors¹ can occur in moving cells², or in cells forming spontaneously a uropod^1,2. These phenomena, which cannot be explained by considering the membrane purely as a fluid, have been attributed to direct or indirect effects of interactions of membrane proteins with the cytoplasmic structures responsible for locomotion and for the change in cell shape^1–3. Here I describe another situation in which a non-uniform distribution of s-Ig is generated during an alteration of the spherical shape of the cell, that is, during formation of microvilli. Such a distribution was not detected in previous transmission immuno-electron microscopy studies, but the microvilli were usually poorly developed. A preferential staining of s-Ig on microvilli has been observed by immunofluorescence⁴, whereas contrasting results (either a uniform⁵ or a non-uniform⁶ distribution) were obtained by scanning electron microscopy using large polyvalent immunolatex particles as markers. I have reinvestigated the point by thin section electron microscopy using a monovalent immunoferritin label in conditions in which microvilli formation, and hence the fraction of membrane on microvilli, is greatly enhanced by ATP deprivation (compare ref. 6). The results show that the label is preferentially concentrated on microvilli.