Three day neonatal thymectomy selectively depletes NK1.1+ T cells.

Neonatal thymectomy of mice 3 days after birth but not at birth leads to T cell-mediated, organ-specific, autoimmune disease in a strain-dependent manner. The mechanisms that lead to disease in this model remain unknown, but the answer may lie in a deficiency of thymus-dependent cells or factors. One candidate is the relatively rare population of NK1.1 + T cells (NKT cells). Conventional alphabetaTCR+ T cells appear in the thymus from days 17-18 of embryogenesis and start emigrating to the periphery around birth, whereas the development of NKT cells is thought to be delayed until at least 1 week after birth. We have confirmed this to be the case in both (BALB/c x C57BL/6)F1 (autoimmune susceptible) and C57BL/6 (autoimmune resistant) mice. Moreover, examination of T cells (in spleen, lymph nodes, liver and bone marrow) from mice following 3 day neonatal thymectomy revealed a significant reduction in the presence of NKT cells in all tissues. However, the extent of depletion was generally more pronounced in (BALB/c x C57BL/6)F1 than in C57BL/6 mice, and the few remaining NKT cells in C57BL/6 mice were enriched for a CD4-CD8int subset which is absent from the thymus and may represent a distinct lineage of thymus-independent NKT cells. Given mounting evidence of a role for NKT cells in protection from autoimmune disease, it is possible that their specific removal by neonatal thymectomy may contribute to the susceptibility of these mice to autoimmune disease.