Identification of immunoglobulin isotypes on human B lymphocytes

Improved detection of rare CALLA-positive cells in peripheral blood using multiparameter flow cytometry

A major limitation to the detection of rare cell types in the peripheral blood using monoclonal antibodies is nonspecific binding of the antibody reagent to normal cells. Detection of rare common acute lymphoblastic leukemia antigen (CALLA)-positive cells in peripheral blood is significantly improved by using multiple flow cytometric parameters to exclude a variety of mature blood cells which may nonspecifically bind the antibody reagent. Monocytes and granulocytes are excluded by gating out cells with high 90 degrees light scatter. By gating on red fluorescence, a variety of mature cell types binding to phycoerythrin (PE)-conjugated Leu 3, Leu 2, and M3 monoclonal antibodies are also excluded. CALLA-positive lymphoblasts from 6 consecutive patients were not excluded on the basis of these parameters. Gating on log 90 degrees light scatter and log red fluorescence in this fashion reduced the incidence of nonspecific binding to peripheral blood mononuclear cells of a fluorescein-conjugated irrelevant monoclonal antibody by 98% from 308 cells per million to 5 cells per million. One CALLA-positive lymphoblast per 100,000 peripheral blood mononuclear cells could be detected in mixture experiments using this method. The normal range of CALLA-positive cells in adults is less than 16 cells per million peripheral blood mononuclear cells. This low background of CALLA-positive peripheral blood cells may permit the detection of early leukemic relapse in acute lymphoblastic leukemia by analysis of the peripheral blood. This methodology can be applied to the detection of any rare cell type by using phycoerythrin-conjugated antibodies to markers that the cell type does not possess.

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.