Fetal type lymphocytes in insulin dependent diabetes mellitus

CD5+ B and gamma/delta T lymphocytes constituting a major population in the fetus and newborn infant, represent two small subsets of the B and T lymph ocyte compartment in healthy adults. There is evidence for their potential involvement and relative expansion in autoimmune disorders. In insulin-depe ndent diabetes mellitus (IDDM) CD5+ B lymphocyte counts have been found to be increased or normal. The aim of our study was to determine the percentag e of both "fetal type" lymphocyte subsets in peripheral blood of 22 recentl y diagnosed children with IDDM, in that of 13 high risk subjects (islet cel l antibody (ICA) positive non-diabetic Ist degree relatives of diabetic chi ldren) and in 43 healthy controls. The percentage of gamma/delta TCR+ cells and of CD5+ B lymphocytes was found to be significantly (p < 0.0001 and p = 0.03, respectively) higher in the diabetic and prediabetic groups as comp ared to controls. Young children with IDDM associated antibodies carry a hi gher risk of developing clinical IDDM than older individuals. In our hands, the percentage of both CD5+ B and gamma/delta T lymphocytes was higher in the younger population. However, age-dependent decrease for both lymphocyte subpopulations in IDDM-prediabetic patients was less than in healthy contr ols. Since the above subpopulations are supposed to play a role in immune r esponse to conserved structures, these observations would suggest a higher capacity of older individuals to "natural autoimmunity" and would explain a t least in part the increased risk of antibody positive young children to d evelop IDDM.