Fibonectin is a component of the surface coat of human neutrophils

Although adherence to surfaces is central to neutrophil function many of the determinants of neutrophil adherence are still unknown. The possible involvement of cell surface material, fibronectin in particular, was therefore studied. Surface coat material was visualized ultra-structurally by the ferrocyanide-reduced osmium technique of Karnovsky (1971). Loosely attached surface coat material was seen distributed uniformly on cells in suspension. Indirect immunoftuorescence indicated the presence of fibronectin on the neutrophil surface. Distri-bution of fibronectin as determined by indirect immunoferritin localization corresponded with the distribution of cell coat material. Some, if not all, of this fibronectin was synthesized by neutrophils themselves since metabolically labelled fibronectin could be obtained by immunoprecipitarion after short-term culture with [ssS]methionine. Neutrophils also adhere to Sepharose beads to which gelatin is covalently linked (GS) but not to plain Sepharose beads (PS). In the process they transfer surface coat material to GS but not PS. Similar transfer was seen when cells were permitted to adhere to glass or plastic coverslips. Indirect immunofiuorescence showed that fibronectin-containing material was transferred from neutro-phils to GS but not PS. Parallel studies with antisera to 2 other plasma proteins, factor VIIIR and alpha1-antitrypsin showed that neutrophils did not transfer these to either GS or PS beads. The data suggest that material antigenically and functionally related to fibronectin is associated with the extracellular coat of neutrophib and is transferred with cell surface material to surfaces to which neutrophils adhere