Antibodies to a cell surface histone-like protein protect against Histoplasma capsulatum
Joshua D. Nosanchuk, Judith N. Steenbergen, Li Shi, George S. Deepe Jr., Arturo Casadevall
Joshua D. Nosanchuk, Judith N. Steenbergen, Li Shi, George S. Deepe Jr., Arturo Casadevall
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Article Infectious disease

Antibodies to a cell surface histone-like protein protect against Histoplasma capsulatum

Abstract

A protective role for antibodies has not previously been described for host defense against the pathogenic fungus Histoplasma capsulatum (Hc). Mouse mAb’s were generated from mice immunized with Hc yeast that binds the cell surface of Hc. Administration of mAb’s before Hc infection reduced fungal burden, decreased pulmonary inflammation, and prolonged survival in a murine infection model. Protection mediated by mAb’s was associated with enhanced levels of IL-4, IL-6, and IFN-γ in the lungs of infected mice. The mAb’s increased phagocytosis of yeast by J774.16 cells through a CR3-dependent process. Ingestion of mAb-opsonized Hc by J774.16 macrophage-like cells was associated with yeast cell growth inhibition and killing. The mAb’s bound to a 17-kDa antigen expressed on the surface of Hc. The antigen was identified as a histone H2B–like protein. This study establishes that mAb’s to a cell surface protein of Hc alter the intracellular fate of the fungus and mediate protection in a murine model of lethal histoplasmosis, and it suggests a new candidate antigen for vaccine development.

Authors

Joshua D. Nosanchuk, Judith N. Steenbergen, Li Shi, George S. Deepe Jr., Arturo Casadevall

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Figure 5

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Intracellular fate of Hc. Black bars represent 100 μg/ml mAb 9C7, white ...
Intracellular fate of Hc. Black bars represent 100 μg/ml mAb 9C7, white bars 5C11 isotype-matched control mAb, and gray bars PBS. Student’s t test was used to analyze the data in each panel. (a) Effect of IgM on Hc phagocytosis. Phagocytosis, by J774.16 macrophage-like cells, of Hc incubated with or without protective mAb in the presence or absence of mAb to CD11a, CD11b, CD11c, or CD18. Phagocytosis was performed without complement. Bars are the average of measurements from three wells (five fields each), and error bars denote SD. *P < 0.001 comparing phagocytic index of Hc with mAb 9C7 or control mAb for each condition examined. **P < 0.001 comparing phagocytic index of mAb 9C7 in the absence vs. the presence of complement receptor blockage. ***P < 0.001 comparing mAb 9C7 and PBS. (b) Phagocytosis of Hc by CHO cells. Phagocytosis of Hc incubated with protective or nonspecific mAb in the presence of CHO cells expressing CR1, CR3, CR4, LFA1, or no receptor. The experiment was done without complement. Bars are the average of measurements from three wells (five fields each), and error bars denote SD. A significant difference was seen between mAb’s in CHO cells expressing CR3 (*P < 0.001). (c) Effect of specific mAb on the growth of Hc. The incorporation of [3H]leucine was significantly lower for Hc phagocytosed by J774.16 cells in the presence of mAb 9C7 compared with controls (*P < 0.001). Bars are the average of measurements from five wells, and error bars denote SD. (d) Hc growth was inhibited and killing occurred when the yeast was phagocytosed by J77416 macrophages in the presence of protective mAb. Yeast cells replicated when phagocytosed in the absence of protective mAb. The difference in percentage growth between yeast incubated with mAb 9C7 and controls was significant (*P < 0.001). Bars are the average of measurements from five plates, and error bars denote SD. Each experiment was repeated at least once, and similar results were obtained.