More than 80% of urinary tract infections in adults are caused by Escherichia coli (31). For E. coli, different factors of virulence, e.g., lipopolysaccharides (LPS), hemolysins, or various types of fimbriae, have been characterized (8). Multiple lines of evidence have emerged concerning the involvement of proximal tubular epithelial cells (TEC) in the renal immune response. These cells have been shown to express major histocompatibility complex (MHC) class II antigens, which are essential for antigen presentation to CD4 ϩ lymphocytes (32) and cellular adhesion molecules crucial for leukocyte migration, e.g., intercellular adhesion molecule-1 (16, 18) and VCAM-1 (6). They are capable of processing and presenting foreign antigen (27) and, besides other cytokines, produce different chemokines, a group of low-molecular-weight cytokines with chemotactic functions. So far, the secretion of RANTES (14), MCP-1 (10), ENA-78 (28), and interleukin-8 (IL-8) (29) has been studied in TEC. Secretion of IL-8 is supposed to be of major relevance for the influx of neutrophils after bacterial contact. In earlier studies we showed that, in contrast to renal carcinoma cells (3), the expression of MHC class II molecules and intercellular adhesion molecule-1 by TEC could not be significantly enhanced by S fimbriae, LPS, or E. coli (21, 23). Furthermore, the secretion of IL-6, tumor necrosis factor alpha, and IL-8 by TEC grown as monolayers could be stimulated by cytokines, but not by S fimbriae, LPS, or E. coli (23). Concerning signalling of TEC directed to the basolateral environment, the in vitro model of monolayer cultures grown on a continuous surface has its limitations. Therefore, we tested whether basolaterally directed IL-8 secretion by TEC differs from luminal secretion and, if so, whether basolaterally directed IL-8 secretion can be stimulated by virulence factors of E. coli.
MATERIALS AND METHODSPrimary cell culture of TEC and electron microscopy. Normal renal tissue was obtained in the local Department of Urology from nephrectomies due to tumors (23). Cells were grown from 1-mm 3 pieces of renal cortex in Dulbecco's modified Eagle medium-Ham's F-12 medium (BioWhittaker, Heidelberg, Germany) supplemented with epidermal growth factor (10 ng/ml), insulin-transferrin-sodiumselenite medium supplement (5 mg/liter), hydrocortisone (37.4 g/liter), 3,3-5-triiodo-L-thyronine (40 mg/liter), penicillin (100 U/ml), streptomycin (100 g/ ml), and 1 M HEPES buffer (15 ml/liter of medium). All supplements were obtained from Sigma, Deisenhofen, Germany, except for penicillin and streptomycin (BioWhittaker). The purity and proximal tubular origin of each cell culture were determined by immunohistochemistry by using anti-cytokeratin (Dianova, Hamburg, Germany), anti-APM (kindly provided by J. E. Scherberich, Frankfurt, Germany), anti-CD68, and anti-factor VIII antibodies (both from Dako, Hamburg, Germany) (21) and by electron microscopy. The ultrastructure of TEC with a microvillus surface is presented in Fig. 1. For electron microscopy, sma...