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 lymphocyte compartment in healthy adults. There is evidence for their potential involvement and relative expansion in autoimmune disorders. In insulin-dependent diabetes mellitus (IDDM) CD5+ B lymphocyte counts have been found to be increased or normal. The aim of our study was to determine the percentage of both "fetal type" lymphocyte subsets in peripheral blood of 22 recently diagnosed children with IDDM, in that of 13 high risk subjects (islet cell antibody (ICA) positive non-diabetic Ist degree relatives of diabetic children) 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 compared to controls. Young children with IDDM associated antibodies carry a higher 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 controls. Since the above subpopulations are supposed to play a role in immune response to conserved structures, these observations would suggest a higher capacity of older individuals to 'natural autoimmunity" and would explain at least in part the increased risk of antibody positive young children to develop IDDM.