Monoclonal Antibodies to Heat Shock Protein 60 Alter the Pathogenesis ofHistoplasma capsulatum

Abstract

Heat shock proteins with molecular masses of ∼60 kDa (Hsp60) are widely distributed in nature and are highly conserved immunogenic molecules that can function as molecular chaperones and enhance cellular survival under physiological stress conditions. The fungus Histoplasma capsulatum displays an Hsp60 on its cell surface that is a key target of the cellular immune response during histoplasmosis, and immunization with this protein is protective. However, the role of humoral responses to Hsp60 has not been fully elucidated. We generated immunoglobulin G (IgG) isotype monoclonal antibodies (MAbs) to H. capsulatum Hsp60. IgG1 and IgG2a MAbs significantly prolonged the survival of mice infected with H. capsulatum. An IgG2b MAb was not protective. The protective MAbs reduced intracellular fungal survival and increased phagolysosomal fusion of macrophages in vitro. Histological examination of infected mice showed that protective MAbs reduced the fungal burden and organ damage. Organs of infected animals treated with protective MAbs had significantly increased levels of interleukin-2 (IL-2), IL-12, and tumor necrosis factor alpha and decreased levels of IL-4 and IL-10. Hence, IgG1 and IgG2a MAbs to Hsp60 can modify H. capsulatum pathogenesis in part by altering the intracellular fate of the fungus and inducing the production of Th1-associated cytokines.

Fungal Vaccines and Immunotherapeutics

“…For example, H1C, an IgG1 mAb specific for an uncharacterized 70-kDa protein on the surface of H. capsulatum, showed no protective effect when given 2 h before challenge, despite enhancing phagocytosis by a murine macrophage cell line (J774.16) (Lopes et al 2010). In contrast, the same group treated mice in a similar fashion with IgG1 mAbs against heat shock protein 60, and these mice were protected from infection (Guimaraes et al 2009). This discrepancy illustrates how the identity of the antigen targeted by an antibody is an important factor in determining its effectiveness.…”

Agglutination ofHistoplasma capsulatumby IgG Monoclonal Antibodies against Hsp60 Impacts Macrophage Effector Functions

“…Although MAbs to H2B increased phagocytosis of yeast through a CR3-dependent process, the intracellular growth and survival of the opsonized yeast were reduced (31,32). IgG1 and IgG2a subclass MAbs to surface Hsp60 also bound H. capsulatum and activated the antifungal properties of macrophages in a dosedependent manner, as described in other pathogen-antibody models, including with antibody interactions with other fungi (11,27) and for antibodies to pathogen heat shock proteins (21,49). Interestingly, increased rates of phagocytosis by the IgG1 subclass MAbs was primarily via Fc receptors, whereas the IgG2a MAbs utilized both Fc and CR3 receptors to augment phagocytosis (11).…”

“…However, ingestion of opsonized H. capsulatum can stimulate significant oxidant release (5,47), suggesting that induction of the respiratory oxidative burst may occur upon Fc-mediated phagocytosis. Although experimental findings suggest that the protective response against histoplasmosis is mainly cellular, we have demonstrated that monoclonal antibodies (MAbs) can modify the pathogenesis of histoplasmosis to benefit the host (11,12,31,32). However, the mechanisms involved in humoral protection against H. capsulatum yeast cells are not fully understood.…”

“…However, the mechanisms involved in humoral protection against H. capsulatum yeast cells are not fully understood. Immunoglobulin M (IgM) MAbs against the histone 2B-like protein (H2B) and IgG1 and IgG2a against the Hsp60 protein reduced the H. capsulatum fungal burden, decreased pulmonary inflammation, and prolonged survival in a murine infection model (11,31,32). In contrast, an IgG2b MAb to Hsp60 was not protective (11).…”

“…Immunoglobulin M (IgM) MAbs against the histone 2B-like protein (H2B) and IgG1 and IgG2a against the Hsp60 protein reduced the H. capsulatum fungal burden, decreased pulmonary inflammation, and prolonged survival in a murine infection model (11,31,32). In contrast, an IgG2b MAb to Hsp60 was not protective (11). Protection mediated by MAbs was associated with enhanced levels of interleukin-4 (IL-4), IL-6, and gamma interferon (IFN-␥) in the lungs of infected mice.…”