Phospholipase B activity enhances adhesion of Cryptococcus neoformans to a human lung epithelial cell line

Abstract

Secreted phospholipase B (PLB1), which contains three enzyme activities in the one protein, is necessary for the initiation of pulmonary infection by Cryptococcus neoformans and for dissemination from the lung via the lymphatics and blood. Adhesion to lung epithelium is the first step in this process, therefore we investigated the role of PLB1 in adhesion to a human lung epithelial cell line, A549, using C. neoformans var. grubii wild-type strain H99, a PLB1 deletion mutant (Δ plb1), and a reconstituted strain (Δ plb1 rec ). Adhesion of H99 and Δ plb1 rec was approximately 69% greater than Δ plb1 at 4 h. Adhesion of Δ plb1 significantly increased after killing by chemicals or heat, and Fourier-transformed analysis by FTIR spectroscopy indicated this was due to changes in capsular and/or cell wall polysaccharides and proteins. Inhibition by specific PLB1 antibodies, or inhibitors of phospholipase B (PLB), but not lysophospholipase (LPL) or lysophospholipase transacylase (LPTA) activities decreased the adhesion of H99 and Δ plb1 rec by 33–58%. Growth under conditions of osmotic stress and high glucose concentration increased both PLB secretion and subsequent cryptococcal adhesion. Dose-dependent increases (to 67%) in adhesion of live Δ plb1 were observed in the presence of 0.1–2 mM palmitic acid. We conclude that PLB1 plays a role in the binding of C. neoformans to host lung epithelial cells, possibly due to production of fatty acids from plasma membranes and/or surfactant by PLB activity.