CD1-RESTRICTED CD4(-CELLS IN MAJOR HISTOCOMPATIBILITY COMPLEX CLASS II-DEFICIENT MICE() T)

Rather unexpectedly, major histocompatibility complex class II-deficie nt mice have a significant population of peripheral CD4(+) T lymphocyt es. We have investigated these cells at the population and clonal leve ls. CD4(+) T lymphocytes from class II-deficient animals are thymicall y derived, appear early in ontogeny, exhibit the phenotype of resting memory cells, are potentially functional by several criteria, and have a diverse T cell receptor repertoire. They do not include substantial ly elevated numbers of NK1.1(+) cells. Hybridomas derived after polycl onal stimulation of the CD4(+) lymphocytes from class II-deficient ani mals include a subset with an unusual reactivity pattern, responding t o splenocytes from many mouse strains including the strain of origin. Most members of this subset recognize the major histocompatibility com plex class Ib molecule CD1; their heterogenous reactivities and T cell receptor usage further suggest the involvement of peptides and/or hig hly variable posttranslational modifications.