Neutrophil transmigration in renal proximal tubular LLC-PK1 cells

Background/aims: Adhesion of intratubular leukocytes to proximal tubules in biopsies of patients with rapidly progressive glomerulonephritis and the appearance of leukocytes in the urine in interstitial nephritis suggest interactions between leukocytes and tubular epithelia in renal disease. The present study was performed to investigate whether incubation of tubular epithelia with cytokines or endotoxin (LPS) does stimulate adhesion and migration of leukocytes through these epithelia in vitro.

Methods: Experiments determined adhesion of PMN to LLC-PK cells cultured on tissue culture plates and transepithelial migration (TEM) through LLC-PK monolayers cultured on microporous membranes. Measurements of transepithelial electrical resistance (TER), cytokine release into apical or basolateral compartments and chemotactic activities of apical and basolateral supernatants were performed.

Results: Preincubation of LLC-PK cells with either TNFalpha or LPS resulted in stimulation of PMN adhesion and consequently PMN migration through LLC-PK monolayers in both apical-to-basolateral and basolateral-to-apical direction. TEM was not associated with a reduction of TER. Although largely apical IL-8 secretion by LLC-PK cells was found, apical-to-basolateral migration occurred against a concentration gradient of IL-8 and could not be inhibited by IL-8 antibodies. Chemotactic activities of supernatants were slightly increased by TEM but did not show any significant differences between apical and basolateral compartments independent of the direction of PMN migration. TEM in basolateral-to-apical direction was about twice as efficient as in apical-to-basolateral direction (Transmigration Index = 3,92 +/- 0,55 and 2,28 +/-,21, respectively). Only basolateral-to-apical TEM could be partly inhibited by preincubation of basolateral membrane with IL-8 antibodies.

Conclusion: Inflammatory mediators stimulate PMN adherence to LLC-PK cells and subsequently TEM. The mechanisms involved in TEM stimulated by cytokines or endotoxin appear to be rather changes in surface receptor properties of LLC-PK cells than chemotactic stimuli. Basolateral-to-apical TEM appears to be the favored direction most likely augmented by IL-8 associated haptotactic PMN stimulation.