Histoplasma capsulatum Cyclophilin A Mediates Attachment to Dendritic Cell VLA-5

Histoplasma capsulatum (He) is a pathogenic fungus that replicates in macrophages (M phi). In dendritic cells (DC), He is killed and fungal Ags are processed and presented to T cells. DC recognize He yeasts via the VLA-5 receptor, whereas M phi recognize yeasts via CD18. To identify ligand(s) on He recognized by DC, VILA-5 was used to probe a Far Western blot of a yeast freeze/thaw extract (F/TE) that inhibited He binding to DC. VLA-5 recognized a 20-kDa protein, identified as cyclophilin A (CypA), and CypA was present on the surface of He yeasts. rCypA inhibited the attachment of He to DC, but not to M phi. Silencing of He CypA by RNA interference reduced yeast binding to DC by 65-85%, but had no effect on binding to M phi. However, F/TE from CypA-silenced yeasts still inhibited binding of wild-type He to DC, and F/TE from wild-type yeasts depleted of CypA also inhibited yeast binding to DC. rCypA did not further inhibit the binding of CypA-silenced yeasts to DC. Polystyrene beads coated with rCypA or fibronectin bound to DC and M phi and to Chinese hamster ovary cells transfected with VLA-5. Binding of rCypA-coated beads, but not fibronectin-coated beads, was inhibited by rCypA. These data demonstrate that CypA serves as a ligand for DC VLA-5, that binding of CypA to VLA-5 is at a site different from FN, and that there is at least one other ligand on the surface of He yeasts that mediates binding of Hc to DC. The Journal of Immunology, 2008, 181: 7106-7114.