Thymocytes can be stimulated to give a strong vaccinia virus-immune cytotoxic T lymphocyte response.

The emergence of virus-specific cytotoxic T lymphocyte (CTL) precursors in thymus can be examined directly by stimulating thymocytes for 6 days in irradiated, virus-infected recipients. Responsiveness is a characteristic of the thymocytes themselves and does not reflect the presence of contaminating, blood-bourne T cells. Strong CTL activity may be generated earlier from thymus than from spleen or lymph node of lethally irradiated, bone marrow reconstituted mice. Also, the reconstitution of virus-immune CTL function in these peripheral lymphoid organs is thymus-dependent. Use of this simple experimental protocol offers considerable possibilities for the analysis of the role of the thymus in the ontogeny of the T cell repertoire.