Decreased surface antigen density on lymphocytes of elderly humans

The aim of our study was to analyze some poorly investigated and controversial aspects of senescent lymphocyte phenotype and functions. We examined 100 healthy aging individuals, divided into 4 age groups, and 30 young controls, correlating lymphocyte responsiveness to mitogenic stimulation with membrane phenotypic pattern and surface molecular densities of the main functional lymphoid markers. Stability of values in the period of study was established. No age-related differences in the parameters evaluated were detected among aging subjects. Phytohemagglutinin-induced lymphocyte proliferation was found severely impaired (about halved) in all elderly individuals with respect to controls. There was no significant difference between elderly group and controls in CD2, CD3, CD4, CD8, CD19, CD25 and HLA-DR antigen distribution. CD56 positive cell percentages were slightly decreased in the elderly groups. In apparent correlation with reduced lymphocyte responsiveness, CD2, CD3, CD4 and CD8 molecular densities, to different extents, were found relevantly (about 1 to 3-fold) lower in all aging groups than in controls. We could not ascertain if those antigens were poorly synthesized, defectively transported to membrane or shed in excess. However, we suggest that decreased surface molecular densities of antigens involved in functional processes of immune responses may be responsible for an abnormal costimulatory pattern during lymphocyte activation, leading to apoptotic rather than proliferative signals in a greater proportion of cells than normal.