Lymphocyte subsets in the young and aging marmoset (Callithrix jacchus).

T lymphocytes were studied in healthy young and old marmosets (Callithrix jacchus). Data indicate that monoclonal antisera to human T lymphocyte antigens can be used to identify these cells in marmosets. Total T and suppressor T cells were lower in the older group; there were no differences in helper T or in B cells. Helper/suppressor ratios (T4/T8) were increased in the older group. Thus, immune system alternations with aging and/or immune deficiency syndromes may be studied in this animal model using available reagents.