Surfactant protein D interacts with Pneumocystis carinii and mediates organism adherence to alveolar macrophages.

TLDR

Pneumocystis carinii uses its mannose‑rich gpA to interact with lower respiratory tract glycoproteins, while surfactant protein D, a calcium‑dependent lectin in the airspace lining, can bind microbial glycoconjugates. The study aimed to determine SP‑D distribution in the lower respiratory tract during Pneumocystis pneumonia in immunosuppressed rats and to assess its influence on organism–macrophage interactions. Using an immunosuppressed rat model of Pneumocystis pneumonia, the authors quantified SP‑D presence in alveolar exudates and investigated its binding to P. carinii and subsequent effects on macrophage adhesion.

Abstract

Pneumocystis carinii interacts with glycoproteins present in the lower respiratory tract through its mannose-rich surface antigen complex termed gpA. Surfactant protein D (SP-D) is a recently described component of the airspace lining material that possesses a calcium-dependent lectin domain capable of interacting with glycoconjugates present on microorganisms and leukocytes. Accordingly, we evaluated the extent and localization of SP-D in the lower respiratory tract during Pneumocystis pneumonia in an immunosuppressed rat model and examined its role in modulating interaction of P. carinii with macrophages. We report that SP-D is a major component of the alveolar exudates that typify P. carinii pneumonia and is present bound to the surface of P. carinii organisms in vivo. We further demonstrate that SP-D binds to P. carinii through saccharide-mediated interactions with gpA present on the surface of the organism. Lastly, we show that SP-D augments binding of P. carinii to alveolar macrophages, but does not significantly enhance macrophage phagocytosis of the organism. The interaction of SP-D with gpA represents an additional important component of the host-parasite relationship during P. carinii pneumonia.