Immunoglobulin class commitment exhibited by B lymphocytes separated according to surface isotype.

In order to determine the extent to which B cells exhibit class commitment, the isotype(s) secreted by individual B cells and their progeny was studied in relation to the isotype(s) expressed on the surface of the B cell. Both primary and secondary B cells were separated according to cell surface isotypes and analyzed under optimal stimulation conditions using the T-dependent splenic focus assay. From these studies the following conclusions conclude be made: a) essentially all mature primary B cells appear to express mu on their surface; b) accordingly, the primary B cell population appears to be devoid of B cells expressing solely IgG on their surface; c) the majority of primary B cells in the presence of optimal T cell help have the potential for multiple class production; d) the secretion of IgA coincides with that of IgM and not IgG in its synthesis by immature B cells; e) a substantial proportion of memory B cells bear mu on their surface; f) memory B cells that lack s-mu are unable to yield clones secreting IgM; and g) a substantial proportion of memory B cells have the potential for multiple class production.