Phenotypic characteristics of human monocytes undergoing transendothelial migration

In our study we characterised the immunophenotype of monocytes that migrate d through an endothelial cell (EC) monolayer in vitro. We found that monocy te migration led to an enhanced expression of CD11a, CD33, CD45RO, CD54 [in tercellular cell-adhesion molecule (ICAM)-1] and human leucocyte antigen-DR . The most striking increase was observed for ICAM-1 when ECs were activate d with tumour necrosis factor-alpha and interleukin-1 alpha. The results of our study indicate the following: (1) there is a characteristic immunophen otype on the surface of monocytes after transendothelial migration; (2) thi s phenotype seems to be induced by interactions between monocytes and ECs; and (3) this change is enhanced by the pretreatment of ECs with cytokines. Taken together, the results suggest that local cytokine production activati ng ECs is sufficient to enhance monocyte migration acid that this, in turn, can induce changes consistent with an activated phenotype known to be inte ractive between antigen-presenting cells and T cells. These results have im plications for our pathogenetic insights into rheumatoid arthritis.