Lymphocytes bearing Fc gamma receptors in rheumatoid arthritis. II. Phenotypic characterisation of mononuclear cells forming Facb rosettes in RA.

We have previously reported an increased proportion of Facb-rosette forming cells in the peripheral blood of patients with rheumatoid arthritis in comparison with healthy controls. The present study investigates the surface phenotype of these cells by means of monoclonal antibodies and a variety of rosetting and lymphocyte fractionation techniques. Facb-R+ cells were found to lack surface markers characteristic of T and B lymphocytes. Studies with monoclonal reagents showed a positive reaction with OKIa1, OKM1, and another monocyte-specific antibody. Fac-R+ cells were recognised by anti-HLA-DR reagents but did not bind the monoclonal antibody 17.15 that recognises a determinant on HLA-DR antigens expressed by lymphocytes but not monocytes. These results show that Facb-R+ cells share certain surface characteristics with monocytes, though they are not phagocytic. These observations are consistent with an accessory role for Facb-R+ cells in the immune response.