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Fc-IgM and Fc-IgG Receptors on Human Circulating B Lymphocytes

From the Metabolism Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20014

Abstract

Peripheral blood B cells from normal humans were enriched with rosette techniques (mean 93.5% surface immunoglobulin positive). We studied these purified B cells for the expression of Fc-IgG and Fc-IgM receptors by using bovine red blood cells coated with IgG (EA-IgG) or IgM (EA-IgM). Between 81 and 94% (mean 88.67%) Fc-IgG and between 79 and 97% (mean 87.5%) Fc-IgM receptor positive cells were found by using this sensitive rosette technique.

The Fc-IgG receptor values had a tendency to decrease in culutre at 37°C. In contrast, cultivation at 37°C for 24, 48, and even 72 hr enhanced Fc-IgM receptor expression. Trypsinization (0.25%) removed Fc-IgM receptors, but not Fc-IgG receptors. However, after further cultivation of the trypsinized cells, Fc-IgM receptors were re-expressed on the same or even greater percentages of cells.

Fc-IgM receptors were also detected on monoclonal B cells (chronic lymphatic leukemia cells) expressing surface immunoglobulins with either or heavy chains exclusively. The high percentage of Fc-IgM positive cells in normal peripheral blood B cells, coupled with the observation that the Fc-IgM receptors are not confined to monoclonal B cells with particular classes of surface immunoglobulins, suggests that the Fc-IgM receptor may be present on essentially all B cells. Moreover, our results suggest that most human B cells expressed both Fc-IgM and Fc-IgG receptors simultaneously.

Footnotes

¹ On leave from the University of Vienna, Austria.