Figure 4.

App1 regulates phagocytosis of C. neoformans. (a and b) Absence of App1 (Δapp1) increases attached and ingested cells by AMs. Reconstitution of APP1 gene (Δapp1^Rec) as well as treatment with App1 recombinant protein restores the WT phenotype (a) as compared with the control (b). (c) App1 treatment decreases phagocytosis of C. neoformans WT cells. (d) Ex vivo phagocytosis. Downregulation of Ipc1 and absence of App1 increase phagocytosis of fungal cells by AMs after 2 hours of infection as compared with the WT strain. IPC1^Rec and Δapp1^Rec strains reconstitute the WT phenotype. (e) App1 does not inhibit phagocytosis of antibody-coated erythrocytes. (f) Treatment with App1 inhibits phagocytosis of iC3b/IgM-IgG–coated erythrocytes. WT, WT C. neoformans H99 strain; Δapp1, C. neoformans lacking App1 protein; Δapp1^Rec, Δapp1 reconstituted strain; IPC1^Rec, Ipc1 reconstituted strain; App1 1×, 8 ng of App1 recombinant protein plus 14 ng of contaminating proteins; App1 2×, 3×, 4×, and 5×, two-, three-, four-, and fivefold App1 1× concentration; control 1×, 14 ng of contaminating proteins; control 2×, 3×, 4×, and 5×, two-, three-, four-, and fivefold control 1× concentration.