The mouse-primed lymphocyte typing test. III. Dissociation of T lymphocyte-stimulating determinants and antibody-defined specificities of the I region-associated Ia antigens.

The mouse-primed lymphocyte typing (mPLT) assay, based on the sequential reactivation of specific immunocompetent alloantigen-reactive T blast cells in secondary mixed leukocyte culture (MLC) has been utilized to define the major histocompatibility complex (MHC) I region-, or Class II-associated lymphocyte-stimulating (LS) determinants. The test panel of secondary stimulating cells has been expanded to include 28 B10.W lines (mouse strains carrying MHC regions derived from wild mice); thus, nearly 40 "independently derived" MHC haplotypes are now represented. Data obtained by using mPLT cells generated in primary MLC between I-AB or I-EC subregion disparate strain combinations reveal that 1) an absolute correlation between expression of the serologically defined Ia specificities and capacity to induce subsequent secondary MLC does not exist; 2) based on the apparent genetic derivations of the I-AB and I-EC subregions, T lymphocytes most likely recognize either the beta-chain per se or an interaction product of the alpha- plus beta-chains; and 3) multiple restimulations of mPLT cells with cells expressing cross-reactive serologically defined Ia specificities fail to select for cells with increased reactivity against shared specificities. Based on these observations, we conclude that t and B lymphocytes recognize different antigenic moieties expressed on the MHC Class II antigens.