Soluble Components of Histoplasma Capsulatum var. Capsulatum have Hemagglutinin Activity and Induce Syngeneic Hemophagocytosis In Vitro

Abstract

Histoplasma capsulatum var. capsulatum is a thermally dimorphic fungus that causes histoplasmosis. Fungal hemagglutination activity and cases of reactive hemophagocytic syndrome (RHS) have been reported in the disseminated form of disease. In the present study, soluble components of H. capsulatum var. capsulatum have been investigated for hemagglutinin activity and the capacity to induce hemophagocytosis in the mouse system. To analyze hemagglutinating activity, mouse red blood cells (RBC) (1% v/v in PBS) were incubated (37 degrees C, 1 h) with cell-free antigen (CFAg) from H. capsulatum var. capsulatum (isolate IMT/HC128) (RBC-CFAg) or previously heated CFAg (56 degrees C, 30 min) (RBC-hCFAg) or as control with PBS (RBC-PBS). Hemophagocytosis was analyzed by incubating BALB/c mouse peritoneal phagocytic cells (5 x 10(6) cells) with syngeneic RBC, sensitized or not with CFAg. In addition, mouse polyclonal antibodies were raised against syngeneic RBC-CFAg (anti-RBC-CFAg) and used to analyze CFAg chromatographic fractions (Sephadex G75/120) by immunoenzymatic assay (ELISA). Hemagglutinin activity was observed with RBC-CFAg, but not with RBC-hCFAg or RBC. Also, hemophagocytosis was observed with RBC-CFAg, but not with RBC. The anti-RBC-CFAg antibodies reacted with CFAg fractions corresponding to a molecular mass (MM) higher than 150 kDa. In conclusion, the yeast form of H. capsulatum var. capsulatum releases thermolabile soluble components with hemagglutinin activity and it has been demonstrated for the first time that soluble components of the same fungus induce syngeneic hemophagocytosis in the in vitro mouse system. Also, indirect analysis with antibodies suggests that high-MM components (>150 kDa) are responsible for the interaction with RBC.

Carbohydrate-rich high-molecular-mass antigens are strongly recognized during experimental Histoplasma capsulatum infection

“…Tristão FSM et al -Carbohydrate-rich hMMAg recognition during experimental histoplasmosis A previous study by our group showed the in vitro hemagglutinin activity and syngeneic hemophagocy tosis induction by H. capsulatum soluble antigens, and suggested that high-molecularmass components (>150 kDa) could be responsible for the interaction with red blood cells 16 .…”

“…The CFAg chromatography was performed as previously described 16 , with some modifications. Two milliliters of CFAg (5.7mg/ml) were applied to a Sephadex G75-120 column (1.5 x 22cm, Sigma-Aldrich) buffered with PBS.…”

“…Considering the possible involvement of the high-molecular-mass components (>150kDa) in the interaction with the host red blood cells 16 , in this study we investigated the host humoral immune response against hMMAg during experimental murine histoplasmosis. Our results showed increased levels of IgG anti-hMMAg after infection, mainly at day 28 p.i.…”

“…Previous work has established that the attachment and agglutination of H. capsulatum yeast cells to human erythrocytes is carbohydrate dependent 29 . Moreover, it was suggested that H. capsulatum soluble hMMAg can be involved in the interaction with red blood cells 16 . When we partially characterized the hMMAg fraction, the carbohydrate analysis showed high amounts of carbohydrate in the hMMAg chromatography's fractions.…”

Paracoccidioides restrepiensis B339 (PS3) and P. lutzii LDR2 yeast cells and soluble components display in vitro hemolytic and hemagglutinating activities on human erythrocytes

“…capsulatum var. capsulatum releases thermolabile soluble components with hemagglutinin activity in vitro .…”