CD8aa TCRab intraepithelial lymphocytes MHC restriction (P1462)

Abstract

T lymphocytes develop in the thymus into two major lineages characterized by expression of ab and gd TCR. Each lineage can be further subdivided into distinct subsets that differ in TCR specificity, phenotype and function. CD8aa TCRab intraepithelial lymphocytes (T-IEL) located in the epithelium of the small intestine is phenotypically different from conventional T cells. CD8aa T-IEL have been studied for years however the question of their MHC restriction has not been elucidated. Therefore, we decided to clone TCR isolated from naturally arising CD8aa T-IEL and retrovirally express these TCRs in BM chimera. First, we cloned four TCRab that were expressed retrovirally in RagKO BM chimera. Analysis of the chimera showed that all TCR clones gave rise to T cells. The T cell that developed were CD4-CD8b- but CD8a+ and phenotypically identical to CD8aa T-IEL isolated from wild type mice. In addition, they were preferentially found in the gut. In order to define the MHC restriction of these particular TCRs, BM chimeras in various MHC-deficient backgrounds were generated. Subsequent analysis of the chimera for the presence of CD8aaTCRab IEL demonstrated that they are dependent either on Kb or Db MHC I or b2m-dependent MHC I aside from KbDb. In conclusion, our results indicate that CD8aa T-IEL develops from precursors expressing particular TCRs that allow their engagement in this unique T cell lineage. In addition, CD8aa T-IEL can harbor clones selected on different MHC molecules.