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 between ICAM‐1 and LFA‐1 in target recognition by allospecific and antigen‐specific Tcells at the clonal level, using human and mouse fibroblasts transfected with HLA‐DR1 or DR2 with or without co‐expression of ICAM‐1, as antigen‐presenting cells. The results show a great heterogeneity in the requirements for ICAM‐1/LFA‐1 interactions for antigen‐specific and alloreactive T cell responses and this requirement may depend on the avidity of any particular interaction. The data also show that for most alloreactive clones, ICAM‐1/LFA‐1 adhesion is not sufficient to facilitate efficient T cell recognition of its target molecule. HLA class II recognition by a large proportion of the DR1‐ and DR2‐specific alloreactive clones studied was different for class II molecules expressed on murine or human fibroblasts compared to human lymphoid cells, and was independent of ICAM‐1 expression on the stimulator cells. The inability of some T cell clones to recognize HLA‐class II expressed on non‐lymphoid cells suggests the absence of specific epitopes and could be due to the lack of the relevant peptides, either because they are derived from species‐specific proteins or to differences in processing of endogenous antigen in the transfected stimulator cells. Copyright © 1994 WILEY‐VCH Verlag GmbH & Co. KGaA