Role of fibronectin in Pneumocystis carinii attachment to cultured lung cells.

Abstract

Attachment of pathogens to host cells is a prerequisite for the development of many infections. Pneumocystis cainfif (PC) pneumonia is characterized by attachment of PC trophozoites to the alveolar epithelium. The mechanism of this process is unknown. Fibronectin (Fn) is a glycoprotein present in the alveolar space known to mediate cell-cell attachment, including the attachment of certain pathogens to host epithelial cells. In this study the binding of Fn to PC trophozoites has been characterized in vitro using '25I-Fn. Fn binds saturably and specifically to 6.4 X 105 binding sites per organism with an apparent binding constant, Kd, of 1.2 X 10-8 M. Fn binding to PC was inhibited by the addition of Arg-Gly-Asp-Ser (RGDS), a tetrapeptide containing the active site of the cell-binding domain of Fn. PC attachment to an alveolar epithelial cell line was quantified using 51Cr-labeled PC trophozoites. Attachment was decreased from 24±1.9% to 12.1±1% (P < 0.01) by the addition of an anti-Fn antibody, an effect that could be overcome by the addition of excess free Fn. It is concluded that binding of Fn to PC may be an important initial step in the attachment of the organism to alveolar epithelial cells. Furthermore, it appears that PC recognizes and binds to the RGDS cell attachment site of Fn. (J. Clin. Invest. 1990.

Pneumocystis carinii attachment to cultured lung cells by pneumocystis gp 120, a fibronectin binding protein.

“…Previous work from our laboratory has demonstrated that Fn binding to P. carinji organisms is a saturable and specific process that is essential for optimal P. carinii attachment (13).…”

“…carinii attachment assay. As previously described (13,21), P. carinii attachment to an alveolar epithelial cell line was quantified using 5"Cr-labeled P. carinii organisms. Freshly isolated P. carinii trophozoites were incubated for 18 h in 2 ml of DME containing 0.5 ml of FCS and 50 MCi of 5"Cr sodium chromate (New England Nuclear, Boston, MA).…”

“…P. carinii trophozoites were incubated for 18 h in DME supplemented with glutamine 0.6 mg/ml, penicillin 100 U/ml, streptomycin 100 ,g/ml, amphotericin B 0.5 Mug/ml, gentamicin 4 ,ug/ml, and 0.6 mM EDTA. 1251-Fn (ICN Pharmaceuticals, Inc., Irvine, CA) binding to P. carinii was quantified as previously described (13). Following the 18-h incubation, the P. carinii suspension was centrifuged (1,600 g X 15 min), the supernatant discarded, and the P. carinii-rich pellet was resuspended in DME at 20 X 106/ml.…”

“…carinii mediates attachment ofthe organism to alveolar epithelial cells. Previous work from our laboratory (13) has demonstrated that the cell-adhesive glycoprotein fibronectin (Fn)' binds to P. carinji organisms and is necessary for the optimal attachment of P. carinii to the alveolar epithelial cell line, A549. The results of this study indicate that gp 12O is the site of Fn binding on P. carinji and that gp120, at least in part, is responsible for the attachment of the organism to the alveolar epithelium.…”

Host Cell Invasion by Medically Important Fungi

“…However, this fungus does not invade these cells to any significant degree and intracellular fungi are observed only within macrophages and granulocytes (Hoyte et al 1997;Limper et al 1997). The adherence of P. jirovecii to epithelial cells is mediated through the binding of the extracellular macromolecules fibronectin and vitronectin, which serve as bridging molecules linking the fungus to host cells (Pottratz and Martin 1990b;Pottratz et al 1991Pottratz et al , 1994Limper et al 1993). Vitronectin and fibronectin both interact with b-glucans on the surface of the fungus (Vassallo et al 2001), and fibronectin is also bound by the major surface glycoprotein ( previously termed gp120) of P. jirovecii (Pottratz et al 1991).…”