Mice deprived of exogenous antigenic stimulation develop a normal repertoire of functional T cells.

The development of T cells and the selection of the TCR repertoire in the absence of exogenous antigenic stimulation were investigated. For this purpose germfree BALB/c mice fed an ultrafiltered solution of chemically defined low m.w. nutrients (GF-CD) were used. Previous studies on B cell development and differentiation in GF-CD mice have demonstrated a high reduction in the number of cells secreting Ig of the non-IgM isotypes but an Ig-VH gene usage and a B cell specificity repertoire that is substantially different from that observed in conventional adult mice and more closely resembles that of neonatal conventional mice. In contrast, the present comparison of the various lymphocyte populations in the thymus, lymph nodes, and spleen from GF-CD and conventional mice using flow cytometry analysis revealed no significant differences. Analysis of the TCR-V beta expression on both mature thymocytes and lymph node T cells showed a high degree of similarity between GF-CD and conventional mice. These findings indicate a marked difference in the influence of exogenous antigenic stimulation on the development of B and T cells. Additionally, development in an environment free of exogenous antigenic stimulation allows for full functional maturation of T cells to occur, because MLC showed that GF-CD splenic T cells could mount allogeneic responses in a way similar to T cells generated in a conventional environment. Most importantly, full Th cell function is generated, because activation of GF-CD spleen cells by cross-linking with mAb against CD3 resulted in the induction of cells secreting IFN-gamma and Ig of the non-IgM isotypes, which cannot be detected in GF-CD sera. These findings demonstrate that functional T and B cells develop in mice that have not been exposed to exogenous Ag, and that the TCR repertoire, in contrast to the B cell compartment, is predominantly shaped by endogenously expressed Ag.