Human CD1d functions as a transplantation antigen and a restriction element in mice

To study the potential functions of human CD1d (hCD1d), we developed transgenic (Tg) mice that ectopically express hCD1d under the control of H-2K^b promoter. High levels of hCD1d expression were detected in all Tg tissues tested. Skin grafts from the K^b/hCD1d Tg mice were rapidly rejected by MHC-matched non-Tg recipient mice, suggesting that hCD1d can act as transplantation Ags. Furthermore, we were able to elicit hCD1d-restricted CD8⁺ CTLs from mice immunized with K^b/hCD1d Tg splenocytes. These CTLs express TCR rearrangements that are distinct from invariant TCR of NK T cells, and secrete significant amounts of IFN-γ upon Ag stimulation. Analysis with various hCD1d-expressing targets and use of Ag presentation inhibitors indicated the recognition of hCD1d by CTLs did not involve species or tissue-specific ligands nor require the processing pathways of endosomes or proteasomes. Additionally, the reactivity of hCD1d-specific CTLs was not affected by acid stripping followed by brefeldin A treatment, suggesting that CTLs may recognize a ligand/hCD1d complex that is resistant to acid denaturation, or empty hCD1d molecules. Our results show that hCD1d can function as an alloantigen for CD8⁺ CTLs. The hCD1d Tg mice provide a versatile model for the study of hCD1d-restricted cytolytic responses to microbial Ags.