NKT Cells in the Rat: Organ-Specific Distribution of NK T Cells Expressing Distinct Vα14 Chains

Rat invariant TCR α-chains and NKT cells were investigated to clarify whether CD1d-mediated recognition by NKT cells is conserved further in evolution. Rats had multiple-copies of TRAV14 genes, which can be categorized into two types according to the diversity accumulated in the CDR2 region. Rats retained invariant TCRα forms with the homogeneous junctional region similar to mouse invariant TRAV14-J281. The proportion of invariant TCR among Vα14+ clones was 12.9% in the thymus and increased in the periphery, 31% in the spleen and 95% in hepatic sinusoidal cells. The invariant TRAV14-J281 was expressed by liver sinusoidal and splenic NKT cells with CD8, CD44high, and TCR Vβ8. Type 1 invariant TCRα was expressed more frequently in hepatic lymphocytes, while type 2 invariant TCRα was expressed predominantly in the spleen. Both types of cells cytolyzed to and were stimulated to proliferate by CD1d-expressing cells in a CD1d-restricted manner. These results suggested that rat NKT cells bearing distinct Vα14 chains are distributed in a tissue-specific pattern. NKT cell populations in rats were more variable than those in mice, indicating that they play novel roles in nature. The implication of the molecular interaction between the structurally diverse invariant TCRα and CD1d/ligand complex in different organs is discussed.