Abstract

Age-related reductions in the DNA replication of human peripheral blood B cells have been reported after stimulation by cross-linking surface immunoglobulins (sIg) with the polyclonal activator Staphylococcus aureus Cowan I (SAC). However, little is known about the mechanisms of these age-related impairments. To examine whether these impairments represented defects unique to sIg mediated signalling, B cells from elderly humans were stimulated with SAC, immobilized anti-IgM and with monoclonal antibodies (mAbs) specific for B cell CD20 and CD40 determinants. Regardless of the stimuli or combinations of stimuli, the proliferative responses of B cells from elderly subjects remained 50% or less of the values observed for B cells from young subjects. Also, the failure to fully restore the age-related impairments of B cells could not be attributed to an absolute lack of potentially reactive cells. Supplementation of anti-IgM stimulated B cells from elderly subjects with IL-2, IL-4 or B cell growth factor (BCGF) revealed that BCGF was able to improve the reduced responses to levels approximating B cells of young subjects. The age-related defects were not restricted to B cell DNA replication because reductions in G1 progression of stimulated B cells from elderly subjects were directly demonstrated by decreased [3H]uridine incorporation into de novo RNA synthesis. However, the age-related impairments in RNA synthesis were less severe than those in DNA replication consistent with progressively greater reductions in the abilities of B cells to traverse the entire cell cycle. Other results showed that the reduced DNA replication of B cells from elderly subjects to immobilized anti-IgM with and without IL-2 did not represent a premature exit of B cells from DNA replication and accelerated maturation into antibody producing cells. Thus, these studies demonstrate that age-related impairments exist in activation signals mediated by several types of human B cell determinants and that abnormalities can be detected during pre-S phase events.