DOI Satoru AICHI CANCER CENTER,LAB.OF IMMUNOLOGY,SENIOR RESEARCHER, 免疫学部, 主任研究員 (60227684)
TAKAHASHI Toshitada AICHI CANCER CENTER,VICE DIRECTOR, 副所長 (00124529)
TSUJIMURA Kunio AICHI CANCER CENTER,LAB.OF IMMUNOLOGY,SENIOR RESEARCHER, 免疫学部, 主任研究員 (10227407)
To understand the role of nonclassical MHC class I molecules in the immune system, we have studied mouse TL molecules, a prototype of nonclassical MHC class I mosecules. The specific aims of this study are (a) elucidation of function of TL in T-cell differentiation, (b) identification of TL-binding molecules and (c) delineation of mechanisms for T-cell recognition of TL moleculed and for cytotoxic acitivity against TL^+ cells. The following results have been obtained :
1. Positive selection of gammadelta T-cells by TL expressed on thymocytes. Two transgenic mouse strains expressing a large amount of Tla^a-3-TL molecules have been derived on C3H background (No TL strains expression on thymocytes). One strain shows abnormal thymic develpment and the deviation of T-cell defferentiation toward the gammadelta lineage. The other strain does not show any obvious abnormalities, but gammadelta CTL was specifically induced in this strain, upon the induction of CTL recognizing TL.These results ind
icated conclusively that TL expressed on thymocytes engages in the positive selection of gammadelta T cells.
2. Identification of TL-binding mosecules. TL molecule was first isolated from TL^+ cells using TL-affinity columns. Molecules complexed with TL were then analyzed by Reverse-phase HPLC,an automated amino acid sequencer, and a tandem mass spectrometry. As a control experment, we isolated H-2K^b-binding peptides and determined their individual sequences and the binding motives. Although we isolated TL molecule amount similar to H-2K^b, the identification of TL-binding mosecules have been very difficult. Thus, the results suggested possibilities that (1) N-termini of TL-binding peptides are modified and blocked, (2) non-peptides such as lipids are binding, or (3) no molecules bind to TL.We are now testing these possibilities.
3. Cellular mechanism of CTL acitivity and invovment of CD4 T cells. (a) cytotoxic mechanism of anti-TL CTL.The majority of CTL against RL are alphabeta T-cells although some gammadelta CTL are induced in TL-transgenic mice. In the analysis of alphabeta CTL,they are found to be divided into two groups according to their cytotoxic acitivity against various TL^+ target cells. Type I CTL kills all TL^+ cells regardless of their orgins, while Type II CTL kills only Fas^+TL^+ spleen cells of Tg. Con.3-1 transgenic mouse. Type I CTL mediates its cytotoxicity by perforin/granzyme, while Type II CTL by FasL.The difference of cytotoxic mechanisms among CTL may be resulted from the differnce in the affinity between TL and TCR or from the difference in TL-binding molecules. (b) Involvement of CD4 T cells. CD4 T cells are required for the rcognition of TL as a transplantation rejectio antigen and for the generation of CTL against requires, although TL is a member of MHC class I antigen family. The results indicate that the helper function of CD4 T cells is required for full activation of CD8 effector cells, because the precursor frequency of CD8^+ recognizing TL is too low to mediate skin graft rejection or to induce CTL. Less