Moonlighting Cell Stress Proteins in Microbial Infections by Brian Henderson

Author:Brian Henderson
Language: eng
Format: epub
Publisher: Springer Netherlands, Dordrecht

12.4.2 Targeting Heat Shock Protein 60 with Antibodies

As Hc Hsp60 is an immunogenic molecule, it has been described as a potential target for antibody therapy (Guimaraes et al. 2009, 2011b). MAbs were generated against recombinant Hsp60 and their protective efficacy characterized in mouse models (Guimaraes et al. 2009). Interestingly, IgG2a and IgG1 mAbs to Hsp60 were protective whereas an IgG2b was disease enhancing. Protection was correlated to a reduction of fungal burden, decreased tissue damage, and prolongation in survival (Guimaraes et al. 2009, 2011c). Cytokine analyses revealed that the protective IgG2a mAbs induced a strong Th1-type host response. Notably, the IgG2b recognized the same region on the protein to which a protective IgG1 also bound in a competitive manner, suggesting that protection was strictly regulated by isotype. This finding was supported by data from mice treated with methamphetamine that developed significant increases in their IgG2b levels and also had accelerated and exacerbated disease (Martinez et al. 2009).

The protective mAbs to Hsp60 modified the intracellular fate of the yeast. IgG1 and IgG2a mAbs to surface Hsp60 activated the antifungal properties of macrophages in a dose dependent manner similar to what has been described in other pathogen-antibody models, including antibody interactions with other fungi (Mukherjee et al. 1996; Guimaraes et al. 2009) and for antibodies to heat shock proteins in other pathogens (Zugel and Kaufmann 1999; Macura et al. 2007). Interestingly, increased rates of Hc yeast cell phagocytosis by the IgG1 subclass mAbs was primarily via Fc receptors whereas the IgG2a mAbs utilized both Fc and CR3 receptors to augment phagocytosis (Guimaraes et al. 2009). Phagosomal maturation was significantly increased in the presence of the protective mAbs and correlated with a reduction in intracellular yeast survival. In contrast, yeast cultured with the disease enhancing IgG2b mAb replicated at an enhanced rate within macrophages.

Interestingly, the protective mAbs were noted to induce aggregation of Hc yeast cells (Guimaraes et al. 2011b). Despite the negative charge on the Hc surface due to the presence of α-1,3-glucans on the cell wall, which increases the electrostatic potential surrounding the cells leading to repulsion, agglutination occurred only when cells were brought together due to a result of Brownian movement during which cellular collision permitted interaction. However, Hc yeast aggregation was an effect of concentration, but the magnitude of aggregation efficiency was dependent on the dissociation constant and subclass of each mAb characterized (Guimaraes et al. 2011a). Additionally, we used an optical tweezer to measure real-time interactions between single cells in the presence of opsonins and found a correlation of time for aggregation and binding constant, with the protective mAb being more effective than the non-protective mAb. This study also shows a cooperative function of Fc and CR3 receptor for the phagocytosis of large particles while small aggregates can be phagocytosed mainly through Fc receptors. Overall, it is unclear what the impact of agglutination potential of the antibodies is during infection. However, the antibodies may keep replicating cells agglutinated, which can reduce the dissemination of the fungus, and these clusters of cells may be more effectively targeted by host responses.

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