Fine specificity of a rabbit antibody interacting with human IgG Fc receptor-like molecules

A polyclonal rabbit antibody raised against an Fc receptor (FcR)-like membrane glycoprotein fraction of chronic leukaemic lymphocytes has previously been prepared and partially characterized [1]. This antibody, called AbA, was found to precipitate a 70-kDa and a 45-kDa fraction of the detergent lysate of U937 cells and to inhibit ligand binding to FcγR on the P388D1 murine macrophage cell line. In the present work we have characterised this antibody further. All FcγRII-positive B lymphoblastoid cell lines, as well as resting human B lymphocytes, were positively stained with the AbA antibody. U937 cells were found to be negative, but after stimulation with phorbol ester (PMA), 50% of the cells became positive. AbA antibody did not react with human T cell lines or with the T+0 cell subset of peripheral blood. Monocytes were also negative. On the other hand, AbA antibody exhibited a dose-dependent inhibition of antibody-mediated cytotoxic reaction (ADCC) of monocytes, while not affecting K cell-mediated ADCC. It had an inhibitory effect of EA rosette formation of B cells and stimulated U937 cells. Furthermore, it interacted with the soluble form of FcγRII released by activated B lymphocytes, and - similarily to IgG - precipitated a 33 kDa fraction from the supernatant of B cells. © 1990.