Distribution of integrins on human peripheral blood mononuclear cells

Abstract

The receptors for fibronectin (FN-R) and vitronectin (VN-R) belong to a family of integral membrane glycoproteins known to be involved in cell-extracellular matrix and cell-cell interactions named integrins (FN-R = ß1 integrin and VN-R = ß3 integrin). Adhesion studies using FN-coated plastic dishes and highly purified subpopulations of peripheral blood mononuclear cells (PBMCs) showed a strong binding of monocytes and T lymphocytes to FN but virtually no binding of B cells to FN. Binding of monocytes and T cells to FN could be partially inhibited by a hexapeptide (GRGDSP) containing the adhesive peptide sequence Arg-Gly-Asp (RGD) as well as by an anti-FN-R antibody. The distribution of ß1 and ß3 integrin complexes on PBMCs was characterized by immunoprecipitation of detergent extracts of125I-labeled cells using polyclonal antibodies against these two receptors. Two surface polypeptides corresponding to the a and ß chains of FN-R and VN-R were found on all three cell types. To characterize these receptors further, monoclonal antibodies (MoAbs) against the very late antigens (VLAs) 1, 3 and 5 were used for immunoprecipitation studies. Monocytes and T cells reacted with VLA 5 that was previously identified as the human FN receptor, whereas no labeling with anti-VLA 5 could be shown for B cells. When cell populations were cultured in 10% human serum for 24 hours, an increase in ß1-integrin+ monocytes and T cells was observed. The number of ß3-integrin+ cells remained essentially unchanged. The presence of ß1 and ß3 integrins on monocytes as well as on T and B lymphocytes may be of significance in the ability of these cells to interact with each other and participate in hematopoiesis and certain immune reactions.