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Aggregation of Cryptococcus neoformans by Surfactant Protein D Is Inhibited by Its Capsular Component Glucuronoxylomannan

Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine, Graduate School of Animal HealthUtrecht University,¹ Division of Acute Medicine and Infectious Diseases, University Medical Center, Utrecht, The Netherlands²

Received 13 June 2003/ Returned for modification 28 July 2003/ Accepted 29 September 2003

Cryptococcus neoformans is an opportunistic pathogen invading the immunocompromised host. Infection starts with the inhalation of acapsular or sparsely encapsulated cells, after which capsule synthesis is initiated. The capsule is the main virulence factor of this yeast-like fungus. Pulmonary surfactant protein D (SP-D) is an important component of the local innate defense system. In the present study, interactions of SP-D with intact C. neoformans cells and their isolated capsular components were investigated. Although encapsulated cryptococci were bound, SP-D showed the highest affinity for acapsular C. neoformans. Only acapsular cryptococci were aggregated by SP-D. Furthermore, the cryptococcal capsular components glucuronoxylomannan (GXM) and mannoprotein 1 (MP1) were bound with relatively high affinity, in contrast to GalXM and MP2. Binding as well as aggregation of acapsular C. neoformans by SP-D could be inhibited by GXM in concentrations that are likely to be present in the lung after infection, suggesting that not only the capsule hampers SP-D function within the innate defense system of the lung but also the secreted capsular component GXM.

Editor: T. R. Kozel

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