HUMAN cluster-of-differentiation 1 (CD1) is a family of cell surface glycoproteins of unknown function expressed on immature thymocytes, epidermal Langerhans cells and a subset of B lymphocytes1-3. Three homologous proteins, CD la, b and c, have been defined serologically4, and the CD1 gene locus on human chromosome 1 contains five potential CD1 genes5. Analysis of the predicted amino-acid sequences of CD1 molecules reveals a low but significant level of homology to major histocompatibility complex (MHC) class I and class II molecules5,6, and, like MHC class I molecules, CD1 molecules are associated non-covalently with (β2-microglobulin7. These structural similarities to known antigen-presenting molecules, together with the expression of CD1 on cells capable of antigen presentation, suggest a role for CD1 molecules in antigen recognition by T cells. Here we demonstrate the specific recognition of CDla by a CD4-CD8- αβ T-cell receptor (TCR) expressing cytolytic T lymphocyte (CTL) line and the specific recognition of CD1c by a CD4-CD8minus;γδTCR CTL line. The interaction of GDI-specific CTLs with CD1+ target cells appeared to involve the CD3-TCR complex, and did not show evidence of MHC restriction. These results suggest that for a subset of T cells, GDI molecules serve a function analogous to that of MHG class I and II molecules.
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