STAPHYLOCOCCAL ENTEROTOXIN-A-INDUCED IN-VITRO ADHESION OF HL-60 CELLSTO ENDOTHELIAL-CELLS INVOLVES BOTH SELECTIN AND INTEGRIN FAMILIES OF CELL-ADHESION MOLECULES

In-vivo exposure to the bacterial superantigen Staphylococcal enteroto xin-A (SEA) induces an inflammatory response characterized by rapid,ex travasation of leucocytes and release of excessive amounts of cytokine s. We have utilized an in-vitro adhesion assay to understand the molec ular mechanisms responsible for SEA-induced extravasation of leucocyte s. Stimulation of human umbilical cord endothelial cells (HUVEC) with increasing concentrations of recombinant SEA (rSEA) did not influence the in-vitro adhesion of HL-60 cells to KUVEC, whereas stimulation of HUVEC by interleukin (IL)-1 beta supported adhesion of HL-60 cells. In creased adhesion of HL-60 cells to HUVEC was noted upon stimulation of endothelium with culture medium obtained from human peripheral blood mononuclear cells (PBM) stimulated with recombinant SEA for 24 (CM-SEA 24 h), 72 (CM-SEA 72 h) and 120 h (CM-SEA 120 h), but not after stimu lation with culture medium obtained from control human peripheral bloo d mononuclear cells (CM), suggesting that soluble factors present in t he supernatants play a major role in SEA-induced cell adhesion. While CM-SEA 24 and 72 h induced both a rapid (4 h) and delayed type of adhe sion, CM-SEA 120 h only induced a delayed type of adhesion. Stimulatio n of PBM by SEA resulted in increased levels of IL-1 beta, IL-2 and in terferon (IFN)-gamma after 24h. Further stimulation for 72-120h result ed in a significant increase in the levels of IL-1 beta, IFN-gamma and tumour necrosis factor (TNF). Stimulation of PBM with SEA also result ed in increased levels of soluble and L-selectin in the cell supernata nts. Increased cell-surface expression of E-selectin, ICAM-1, HLA-DR a nd VCAM-1 was detected on HUVEC stimulated with CM-SEA media. While E- selectin and VCAM were induced on HUVEC within a few hours, induction of ICAM and HLA-DR required a longer induction period. Adhesion of HL- 60 cells to HUVEC treated with CM-SEA was inhibited by monoclonal anti bodies (MoAbs) against both the selectin and integrin families of cell adhesion molecules, suggesting that multiple pathways contribute to S EA-induced leucocyte extravasation. The results suggested that selecti n-dependent adhesion was more prominent during the early phase while i ntegrin-induced adhesion occurred at a later stage.