Coexpression of multiple immunoglobulin isotypes on human B-lymphocytes

Endogenous immunoglobulin (Ig) determinants on blood B-lymphocytes (B-cells) were investigated in 13 healthy individuals, 9 patients with thyrotoxic Graves disease, 5 patients with chronic sarcoidosis, and 4 patients with IgA deposition in renal glomeruli. Specificities of goat antisera to Ig determinants were confirmed by studying Ig isotypes on leukemic B-cells. Absence of nonspecific attachment of the goat antisera was ascertained by reacting cells with goat IgG. Lymphocytes were distinguished from monocytes by morphology and by reacting monocytes with rhodamine-conjugated immune complexes. The endogenous nature of the cell surface Ig was established by an antibody-prelabeling technique as follows: after the surface Ig had been labelled with fluorescent antibody, the cells were cultured for 3 days. Antibody-prelabelled surface Ig diminished by the third day of incubation because of shedding. Thus restaining of the cells at the end of the culture identified the membrane Ig determinants expressed during the incubation. Our results indicated that endogenous gamma and alpha chains were present on B-cells of all donors. In Graves disease, epsilon chain was also found. In all cases of Graves disease, 2 cases of sarcoidosis and 2 normal individuals, gamma, alpha, mu and delta chains were present on the majority of B-cells suggesting coexpression of these heavy chains on a single cell. I conclude that all 5 Ig isotypes may be coexpressed on B-cells under certain clinical conditions.