Monoclonal antibody-defined B cell subsets in aging humans and Down's syndrome.

Peripheral blood from aging and young humans and patients with Down's syndrome, and from age- and sex-matched controls, was studied for the proportions of surface immunoglobulin (SIg+) bearing and monoclonal antibodies FMC1, and FMC7 defined B lymphocytes and B lymphocyte subsets using fluorescent-activated cell sorter. In aging humans, the proportion of SIg+ and FMC1+ (that detect all B lymphocytes) were comparable to simultaneously studied healthy young controls. However, FMC7+ (that detects a subset of B cells) B cells were significantly (p less than 0.05) increased when compared to young subjects. In aging subjects, the proportions of FMC7+ B cells were comparable to their FMC1+ B cells, whereas in young subjects FMC7+ B cells were a subset of FMC1+ B cells. In Down's syndrome, a phenomenon similar to aging humans was observed, that is the proportions of FMC7+ were increased when compared to age- and sex-matched controls and were comparable to their own FMC1+ B cells. This study demonstrates the abnormality of B lymphocytes in human aging and Down's syndrome. The significance of these findings is discussed.