Quantitative studies on the precursors of cytotoxic lymphocytes. IV. Specificity and cross-reactivity of cytotoxic clones.

Murine cytotoxic lymphocyte precursor cells (CLP) appear to be specificity restricted, yet 2 to 4% of the total pool appears to be activated in a response against a single foreign H-2 alloantigen. The simplest model that provides enough CLP for all possible reactions is that H-2 antigens have cross-reacting determinants. Experimentally, we observed that activation of RNC-nu/+ (H-2k) LN cells with H-2b spleen cells activated 1200 to 1800 CLP per 10(6) LN cells capable of lysing H-2b target cells. Of these, 3 to 4% could also lyse H-2d target cells. In addition, a small number of clones (approximately 25/10(6) LN cells) were activated which could lyse H-2d but not H-2b target cells. However, the total number of such apparent nonspecifically activated clones is small since greater than 80% of all the CLP activated on culturing with H-2b alloantigens will lyse H-2b targets. The results are discussed in terms of specificity restriction and possible subpopulations of CLP.