DIFFERENT REQUIREMENTS OF ICAM-1 LFA-1 ADHESION IN ALLORECOGNITION AND SELF-RESTRICTED ANTIGEN RECOGNITION BY CLASS II-SPECIFIC T-CELL CLONES/

We have analyzed the influence of non-antigen-specific interactions be tween ICAM-1 and LFA-1 in target recognition by allospecific and antig en-specific T cells at the clonal level, using human and mouse fibrobl asts transfected with HLA-DR1 or DR2 with or without co-expression of ICAM-1, as antigen-presenting cells. The results show a great heteroge neity in the requirements for ICAM-1/LFA-1 interactions for antigen-sp ecific and alloreactive T cell responses and this requirement may depe nd on the avidity of any particular interaction. The data also show th at for most alloreactive clones, ICAM-1/LFA-1 adhesion is not sufficie nt to facilitate efficient T cell recognition of its target molecule. HLA class II recognition by a large proportion of the DR1- and DR2-spe cific alloreactive clones studied was different for class II molecules expressed on murine or human fibroblasts compared to human lymphoid c ells, and was independent of ICAM-1 expression on the stimulator cells . The inability of some T cell clones to recognize HLA-class II expres sed on non-lymphoid cells suggests the absence of specific epitopes an d could be due to the lack of the relevant peptides, either because th ey are derived from species-specific proteins or to differences in pro cessing of endogenous antigen in the transfected stimulator cells.