Differential CD4/CD8 subset-specific expression of highly homologous rat Tcrb-V8 family members suggests a role of CDR2 and/or CDR4 (HV4) in MHC class-specific thymic selection

Role of human and porcine MHC DRB1 alleles in determining the intensity of individual human anti-pig T-cell responses

BACKGROUND

Differences in quality and strength of immune responses between individuals are mainly due to polymorphisms in major histocompatibility complex (MHC) molecules. Focusing on MHC class-II, we asked whether the intensity of human anti-pig T-cell responses is influenced by genetic variability in the human HLA-DRB1 and/or the porcine SLA-DRB1 locus.

METHODS

ELISpot assays were performed using peripheral blood mononuclear cells (PBMCs) from 62 HLA-DRB1-typed blood donors as responder and the porcine B cell line L23 as stimulator cells. Based on the frequency of IFN-γ-secreting cells, groups of weak, medium, and strong responder individuals were defined. Mixed lymphocyte reaction (MLR) assays were performed to study the stimulatory capacity of porcine PBMCs expressing different SLA-DRB1 alleles.

RESULTS

Concerning the MHC class-II configuration of human cells, we found a significant overrepresentation of HLA-DRB1*01 alleles in the medium/strong responder group as compared to individuals showing weak responses to stimulation with L23 cells. Evaluation of the role of MHC class-II variability in porcine stimulators revealed that cells expressing SLA-DRB1*06 alleles triggered strong proliferation in approximately 70% of humans. Comparison of amino acid sequences indicated that strong human anti-pig reactivity may be associated with a high rate of similarity between human and pig HLA/SLA-DRB1 alleles.

CONCLUSION

Variability in human and porcine MHC determines the intensity of individual human anti-pig T-cell responses. MHC typing and cross-matching of prospective recipients of xenografts and donor pigs could be relevant to select for donor-recipient combinations with minimal anti-porcine immunity.

The Complementarity Determining Region 2 of BV8S2 (Vβ8.2) Contributes to Antigen Recognition by Rat Invariant NKT Cell TCR

Invariant NKT cells (iNKT cells) are characterized by a semi-invariant TCR comprising an invariant alpha-chain paired with beta-chains with limited BV gene usage which are specific for complexes of CD1d and glycolipid Ags like alpha-galactosylceramide (alpha-GalCer). iNKT cells can be visualized with alpha-GalCer-loaded CD1d tetramers, and the binding of mouse CD1d tetramers to mouse as well as to human iNKT cells suggests a high degree of conservation in recognition of glycolipid Ags between species. Surprisingly, mouse CD1d tetramers failed to stain a discrete cell population among F344/Crl rat liver lymphocytes, although comprised iNKT cells are indicated by IL-4 and IFN-gamma secretion after alpha-GalCer stimulation. The arising hypothesis that rat iNKT TCR recognizes alpha-GalCer only if presented by syngeneic CD1d was then tested with the help of newly generated rat and mouse iNKT TCR-transduced cell lines. Cells expressing mouse iNKT TCR reacted to alpha-GalCer presented by rat or mouse CD1d and efficiently bound alpha-GalCer-loaded mouse CD1d tetramers. In contrast, cells expressing rat iNKT TCR responded only to alpha-GalCer presented by syngeneic CD1d and bound mouse CD1d tetramers only poorly or not at all. Finally, CD1d-dependent alpha-GalCer reactivity and binding of mouse CD1d tetramers was tested for cells expressing iNKT TCR comprising either rat or mouse AV14 (Valpha14) alpha-chains and wild-type or mutated BV8S2 (Vbeta8.2) beta-chains. The results confirmed the need of syngeneic CD1d as restriction element for rat iNKT TCR and identified the CDR2 of BV8S2 as an essential site for ligand recognition by iNKT TCR.