Selection of the T cell repertoire during ontogeny: Limiting dilution analysis

Abstract

The relative frequencies of cytotoxic T lymphocyte precursors (CTL‐P) specific for minor histocompatibility antigens that are restricted to either k or b major histocompatibility complex antigens in normal B6 mice and in B6 → (B6 CBA)F₁ radiation chimeras were estimated. The ratio of k‐restricted to b‐restricted CTL‐P determined for the radiation chimeras served as a base value to which the ratio of k: b‐restricted CTL from normal B6 mice can be compared. The frequencies of allorestricted CTL‐P in B6 mice were determined after the B6 cells had been depleted of k‐reactive cells by filtration through irradiated B6.H−2^k mice. Lymphocytes from immunized animals were used to obtain frequency estimates of CTL‐P specific for minor H antigens. The cultures contained nu/nu spleen cells syngeneic to the responder, but no exogenous interleukin 2 (T cell growth factor) since a high degree of nonspecific killing was found in IL2‐supplemented cultures. It was found that the CTL‐P frequency of B6 mice to BALB.B antigens in the lymph node cells of normal or immune B6 mice were 1 in 300000 and 1 in 8000, respectively. In B6→ (B6 × CBA)F₁ radiation chimeras, the ratio of BALB.B/BALB.K‐specific CTL‐P was 3 :1s ratio was 17 :1 in normal B6 mice. Twenty‐five percent of CTL clones from normal B6 mice lysing BALB.K target also lysed BALB.B target whereas less than 1% of CTL clones lytic on BALB.K target from the chimeras showed this cross‐reaction The results are compatible with the idea of complete positive selection of self MHC‐restricted CTL‐P in the absence of priming effects by foreign antigen.