REGULATION OF U-937 MONOCYTE ADHESION TO CULTURED HUMAN MESANGIAL CELLS BY CYTOKINES AND VASOACTIVE AGENTS

Leukocyte adhesion to kidney cells is an early event in renal inflammation, such as glomerulonephritis. We developed an experimental model of monocyte adhesion to cultured human mesangial cells. U-937 myelomonocytic leukaemia cells, similar to peripheral blood human monocytes, irreversibly bound to mesangial cell monolayers upon 30-180 min coincubations (to a max. of 13 600+/-1100/cm(2) monolayer), as assessed by cell counting, U-937 labelling with H-3-thymidine, and colorimetry of nuclear staining with crystal violet. Adhesion was enhanced in mesangial cells proliferating in response to 17% fetal bovine serum, indicating expression of a proinflammatory phenotype. E. coli lipopolysaccharide (LPS), tumour necrosis factor-alpha (TNF-alpha) and protein kinase C activation with phorbol myristate acetate (PMA) potentiated monocyte binding during either coincubation or 24-h pretreatment (0.1 mu M PMA, +200+/-21%). Binding was also promoted by pretreatment with vasoconstrictors, such as the thromboxane A(2) mimetic, U-46619 (10 nM-1 mu M, max. +35+/-3%), or 1 mu M angiotensin II (+61+/-4%). To elucidate the mechanisms of monocyte adhesion, we analysed the adhesion molecules expressed by human mesangial cells, employing reverse transcription/polymerase chain reaction to detect ICAM-1, VCAM-1 and E-selectin gene expression. Proliferating cells express VCAM-1 and ICAM-1, confirmed by immunocytochemical staining and 79+/-3% inhibition of stimulated adhesion by pretreatment of mesangial cells with an anti-ICAM-1 monoclonal Ab. E-selectin transcription was not detectable. VCAM-1, but not ICAM-1, mRNA content was increased by LPS and TNF-alpha, while immunostaining of fixed cells indicated stimulation of ICAM-1 and VCAM-1 protein by LPS, TNF-alpha. and, to a lesser extent, U-46619. Thus, post-transcriptional regulation of ICAM-1/VCAM-1 or expression of other adhesion molecules may account for vasoconstrictor-enhanced binding of monocytes to human mesangial cells. These findings underscore the importance of mesangial 'priming' by inflammatory or vasoactive mediators in leukocyte chemoattraction during glomerular disease.