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 inflamma tion, such as glomerulonephritis. We developed an experimental model o f monocyte adhesion to cultured human mesangial cells. U-937 myelomono cytic leukaemia cells, similar to peripheral blood human monocytes, ir reversibly bound to mesangial cell monolayers upon 30-180 min coincuba tions (to a max. of 13 600+/-1100/cm(2) monolayer), as assessed by cel l counting, U-937 labelling with H-3-thymidine, and colorimetry of nuc lear 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 a ctivation with phorbol myristate acetate (PMA) potentiated monocyte bi nding during either coincubation or 24-h pretreatment (0.1 mu M PMA, 200+/-21%). Binding was also promoted by pretreatment with vasoconstri ctors, such as the thromboxane A(2) mimetic, U-46619 (10 nM-1 mu M, ma x. +35+/-3%), or 1 mu M angiotensin II (+61+/-4%). To elucidate the me chanisms of monocyte adhesion, we analysed the adhesion molecules expr essed by human mesangial cells, employing reverse transcription/polyme rase chain reaction to detect ICAM-1, VCAM-1 and E-selectin gene expre ssion. Proliferating cells express VCAM-1 and ICAM-1, confirmed by imm unocytochemical 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 L PS, TNF-alpha. and, to a lesser extent, U-46619. Thus, post-transcript ional regulation of ICAM-1/VCAM-1 or expression of other adhesion mole cules may account for vasoconstrictor-enhanced binding of monocytes to human mesangial cells. These findings underscore the importance of me sangial 'priming' by inflammatory or vasoactive mediators in leukocyte chemoattraction during glomerular disease.