Myeloid C-type lectin receptors that recognize fungal mannans interact with Pneumocystis organisms and major surface glycoprotein

Myeloid C-type lectin receptors (CLRs) are innate immune recognition molecules that bind to microorganisms via their carbohydrate recognition domains. In this study, we utilized a library of CLRs that recognize fungal mannans. We used this library to screen against Pneumocystis carinii (Pc) homogenates or purified Pc major surface glycoprotein (Msg) present on Pneumocystis. The results demonstrated that all of the mammalian CLR hFc-fusions tested displayed significant interaction/binding with Pc organisms, and furthermore to isolated Msg. Highest Pc organism and Msg binding activities were with CLR members Mincle, Dectin-2, DC-SIGN and MCL. An immunofluorescence assay with the respective CLR hFc-fusions against whole Pc life forms corroborated these findings. Although some of these CLRs have been implicated previously as important for Pneumocystis pathogenesis (Dectin-1/Dectin-2/Mincle), this is the first analysis of head-to-head comparison of known fungal mannan binding CLR-hFc fusions with Pc. Lastly, heat treatment resulted in reducted CLR binding.