MUTATIONS IN HUMAN CD4 IMPAIR THE FUNCTIONAL INTERACTION WITH DIFFERENT HUMAN AND MOUSE CLASS-II ISOTYPES AND ALLELES

The structure-function of the CD4-class II MHC interaction was investi gated, Two functional assays were used to assess the responses of the 3DT52,5,8 murine T cell hybridoma expressing human CD4 (h-CD4) or muri ne CD4 (m-CD4), First, we determined the responses of the CD4(+) and C D4(-) effector cells toward DAP-3 cells co-expressing the cognate allo antigen H-2D(d) together with several human (DRw52b, DR4-Dw4, DR2A, an d DPw2) and murine (I-A(b), I-A(k), I-A alpha(b)I-A beta(k) and I-E(k) ) class II alleles and isotypes, We found that h-CD4 and m-CD4 strongl y enhance the T cell response to H-2D(d), demonstrating that interspec ies CD4/class II interactions occur efficiently, Furthermore, mutation s in h-CD4 at positions 19, 89, and 165 markedly reduced the interacti on with both human class II and mouse class II, indicating that the st ructural features of this cross-species interaction are strongly conse rved, This was further supported by the finding that a h-CD4 deletion mutant (deletion F43-S49) interacted with both human and murine class II, Moreover, as 3DT cells express the responsive V beta element for t he bacterial superantigen staphylococcal enterotoxin 8, a co-receptor assay was conducted, DAP-3 cells expressing only class II molecules we re used as APCs to present staphylococcal enterotoxin B to h-CD4(+) an d m-CD4(+) T cells, h-CD4 and m-CD4 were able to enhance the T cell re sponse to staphylococcal enterotoxin B, further demonstrating the cons ervation of the CD4-class ii MHC interaction.