Vitronectin binds to Pneumocystis carinii and mediates organism attachment to cultured lung epithelial cells

Abstract

Pneumocystis carinii attaches to alveolar epithelial cells during the development of pneumonia. Adhesive proteins found within the alveolar space have been proposed to mediate P. carinii adherence to lung cells. Vitronectin (Vn), a 75-kDa glycoprotein present in the lower respiratory tract, has substantial cell-adhesive properties and might participate in the host-parasite interaction during P. carinii pneumonia. To address whether Vn binds to P. carinii, we studied the interaction of radiolabeled Vn with purified P. carinii organisms. Vn bound to P. carinii, occupying an estimated 5.47 x 105 binding sites per organism, with an affinity constant, Kd, of 4.24 x 10-7 M. Interestingly, the interaction of Vn with P. carinii was not mediated through the Arg-Gly-Asp cell-adhesive domain of Vn. Addition of Arg-Gly-Asp-Ser (RGDS) peptides did not inhibit binding. In contrast, Vn binding to P. carinii was substantially inhibited by the addition of heparin or by * Corresponding author. significance of Vn-microbe interactions in the pathogenesis of infection has not yet been established. Although P. carinii organisms encounter substantial concentrations of Vn in both normal and diseased lung, the role of Vn in P. carinii pneumonia has not been fully studied. Accordingly, this investigation was undertaken to determine whether Vn interacts with purified P. carinii and to determine which regions of Vn interact with the organism. To also determine the potential role of Vn in mediating P. carinii attachment to host epithelial cells, we assessed the impact of Vn in mediating P. carinii attachment to cultured A549 lung cells. MATERIALS AND METHODS Materials. All organic chemicals were of analytical grade and obtained from Sigma Chemical Co. (St. Louis, Mo.) or Fischer Scientific Co. (Pittsburgh, Pa.) unless otherwise specified. Iodo-Beads were obtained from Pierce Chemical Co., Rockford, Ill.; fetal bovine serum was from GIBCO, Grand Island, N.Y.; and carrier-free Na'251 and Rainbow

Translocation of surface antigen genes to a unique telomeric expression site in Pneumocystis carinii

“…Switching may be preprogrammed, particular MSG isoforms being expressed during certain environmental conditions or life-cycle stages (Cushion et al, 1988), or it may be induced by environmental differences encountered by the individual organisms. Even a population of P. c. carinii isolated from the same rat may be subjected to different environments within the animal, perhaps by interacting with any of a number of mammalian proteins known to bind MSG (Pottratz and Martin, 1990;Ezekowitz et al, 1991;Limper et al, 1993). Another possibility is that organisms may vary at random, in which case selection of organisms presenting a particular set of surface determinants could be a factor.…”

Pneumocystis carinii induces interleukin 6 production by an alveolar epithelial cell line

“…Previous work has demonstrated that IL-6 induces production of extracellular matrix proteins from epithelial cells [25]. In addition, other studies have demonstrated that PC attachment to alveolar epithelial cells is primarily mediated by the extracellular matrix proteins Fn [5] and Vn [7]. To determine the effects of IL-6 on A549 cell production of Fn and Vn, A549 cells were incubated in the presence of IL-6 (0-100 ng mL -1 ) for 24 h and levels of both Fn and Vn were quantified in the supernatants.…”

“…Ultrastructural studies have demonstrated close apposition and interdigitation between the outer membrane of PC trophozoites and the cell membrane of type I alveolar epithelial cells [3][4]. Previous studies have demonstrated the importance of the extracellular matrix proteins fibronectin (Fn) and vitronectin (Vn) as mediators of PC attachment to lung epithelial cells in vitro [5][6][7].…”

XVI. The Pneumocystis carinii major surface glycoprotein (MSG): its potential involvement in the pathophysiology of pneumocystosis

“…Several in vitro studies using the human epithelial alveolar cell line A549 (with type II pneumocyte-like properties) have demonstrated that whole P. carinii organisms attach to A549 cells [15,15,16,16]. Binding is mediated by at least two adhesive glycoproteins, ¢bronectin and vitronectin, that bind to both P. carinii and A549 cells, and, thereby, are presumed to facilitate attachment to alveolar epithelium [16,17]. Further, MSG has been identi¢ed as a ¢bronectin binding protein required for P. carinii attachment [18].…”