Human bone marrow-derived IgA is produced by IgA-committed B cells in vitro.

Although human bone marrow has been implicated in the production of serum immunoglobulins, little information is available concerning the kinetics of antibody production (primary- or secondary-type humoral response) or the cells that are responsible for antibody production in human bone marrow. In this study, the kinetics of and cells responsible for antibody production in the bone marrow were investigated. Previous studies have demonstrated that human bone marrow mononuclear cells secrete a significant amount of IgA in vitro. This finding led to the focus of the present investigation on bone marrow IgA production. The results reported here demonstrate that IgA was synthesized de novo in cultures of bone marrow mononuclear cells; its peak concentration in the culture supernatants preceded that of IgM; its production was totally inhibited by the addition of microgram quantities of anti-alpha-chain antiserum, while milligram quantities of anti-mu-chain antiserum were required for even partial inhibition of IgA production; and the culture of isolated IgA-bearing cells resulted in a greater than 13-fold increase in IgA concentration in the culture supernatants as compared with those from unseparated bone marrow mononuclear cells. From this study, it was concluded that bone marrow produces IgA as a secondary or anamnestic response to some undetermined stimulus and that IgA-committed B cells residing in, although probably not stimulated in, the bone marrow compartment were responsible for the IgA synthesis and secretion in vitro.