Biological impact of antibodies to Histoplasma capsulatum antigens

Abstract

Monoclonal antibodies (mAbs) are powerful tools for studying diverse aspects of the biology of pathogenic microbes. We have shown that mAbs to cell surface antigens of Histoplasma capsulatum, including histone 2B and the M antigen, can modify the pathogenesis of histoplasmosis. MAbs to hsp60 can also modify H. capsulatum pathogenesis in part by altering the intracellular fate of the fungus, with reduced intracellular fungal survival characterized by increased phagolysosomal fusion within macrophages in vitro. The protective mAbs significantly prolong the survival of mice infected with H. capsulatum and induce the production of Th1-associated cytokines. Interestingly, the mAbs induce different degrees of yeast cell agglutination in vitro, which we characterized by light microscopy/imaging analysis, flow cytometry, dynamic light scattering (DLS), Zeta-Potential and Optical tweezers. We have found that the amount of Hc aggregation due to Hsp60-binding IgGs is dependent on the (1) concentration of mAbs, (2) mAb binding constant, and (3) IgG subclass. We have further determined that the capacity of IgG mAbs to agglutinate Hc significantly impacts the pathogenesis of histoplasmosis and the effect is isotype and epitope dependent. The mAbs also have facilitated the exploration of protein-protein interactions, allowing us to gain new insights into the regulation and trafficking of key cellular proteins under different temperature stress conditions (i.e. such as dimorphism, stress and pathogenesis). Hence, mAbs are an extraordinary component of our toolbox for the exploration of H. capsulatum. In sum, these results show the complexity of antibody-antigen interactions and the Hsp60 function. We expect that these results will provide a better understanding of H. capsulatum biology that may lead to new avenues for the management of histoplasmosis.