Introduction: the antigen CD28, expressed in most T cells, has co-stimulatory properties and plays a pivotal role in clonal T cell anergy mechanisms.
Methods: we have compared proliferative T cell responses after anti-CD3 or in phorbol myristate acetate activation with concomitant CD28 signal in peripheral blood mononuclear cells from healthy donors aged over 65 [elderly donors; ED] and young healthy donors (YD); mean age 30+/-2.7 years).
Results: no proliferative responses were observed in ED and YD with anti-CD28 monoclonal antibody alone. These responses both were defective in ED, particularly after anti-CD3 monoclonal antibody stimulus (7604 compared with 12,438 c.p.m. in YD, P=0.001) and were corrected when anti-CD28 monoclonal antibody was added to the culture (17,216 vs 18,536, not significant). Functional integrity of the CD28 co-stimulatory pathway was demonstrated by analysis of CD25 expression, interleukin-2 secretion and interleukin-2 gene expression on T cells from ED and YD. Age-associated phenotypic T cell changes were not crucial for an adequate CD28 response.
Conclusion: these experiments demonstrate the integrity of the CD28 pathway in elderly people, and suggest that ageing does not affect different T cell activation pathways equally.