Differential Interaction of the Staphylococcal Toxins Panton–Valentine Leukocidin and γ-Hemolysin CB with Human C5a Receptors

Abstract

Staphylococcus aureus is well adapted to the human host. Evasion of the host phagocyte response is critical for successful infection. The staphylococcal bicomponent pore-forming toxins Panton-Valentine Leukocidin (PVL) and γ-Hemolysin CB (HlgCB) target human phagocytes through interaction with the complement receptors C5aR1 and C5aR2. Currently, the apparent redundancy of both toxins cannot be adequately addressed in experimental models of infection since mice are resistant to PVL and HlgCB. The molecular basis for species specificity of the two toxins in animal models is not completely understood. We show that PVL and HlgCB feature distinct activity towards neutrophils of different mammalian species, where activity of PVL is found to be restricted to fewer species than that of HlgCB. Over-expression of various mammalian C5a receptors in HEK cells confirms that cytotoxicity towards neutrophils is driven by species-specific interactions of the toxins with C5aR1. By taking advantage of the species-specific engagement of the toxins with their receptors, we demonstrate that PVL and HlgCB differentially interact with human C5aR1 and C5aR2. In addition, binding studies illustrate that different parts of the receptor are involved in the initial binding of the toxin and the subsequent formation of lytic pores. These findings allow a better understanding of the molecular mechanism of pore formation. Finally, we show that toxicity of PVL, but not HlgCB, is neutralized by various C5aR1-antagonists. This study offers directions for the development of improved preclinical models for infection, and the design of drugs antagonizing leukocidin toxicity.

Critical Role of Alpha-Toxin and Protective Effects of Its Neutralization by a Human Antibody in Acute Bacterial Skin and Skin Structure Infections

“…In the rabbit model of ABSSSI, rabbits that received prophylaxis with MEDI4893* 24 h before infection exhibited a significant reduction in dermonecrotic ulceration compared to rabbits immunized with c-IgG, a human IgG1 isotype-matched control (P Ͻ 0.01). These results indicate that MEDI4893* can prevent disease not only in mice (18)(19)(20)(21) but also in rabbits, a species that is susceptible to a greater array of S. aureus toxins (7)(8)(9)(10)36).…”

“…Rabbit models have been used since the late 1800s for the study of staphylococcal infection because the course of disease in rabbits closely mimics that in humans (6). Rabbits exhibit susceptibilities to staphylococcal toxins and superantigens remarkably similar to those of humans, whereas mice, rats, and even nonhuman primates are resistant to many of these toxins (7)(8)(9)(10)(11). The pathogenic roles of many staphylococcal toxins, including alpha-toxin, have been validated in different rabbit infection models (6).…”

Safety and immunogenicity of a recombinant Staphylococcus aureus α-toxoid and a recombinant Panton-Valentine leukocidin subunit, in healthy adults

“…43 However, the species-specific interaction between toxins and complement receptors have called into question the applicability of mouse models for evaluating potential virulence factors as vaccine targets. 44,45 Despite these limitations, PVL could play a role as a target for active and passive immunization, due to the structural homology of subunits among members of the bi-component cytotoxin family. 46 This structural homology allows for cross-neutralization of several virulence factors with antibodies generated against a single virulence factor.…”

Targeting fundamental pathways to disrupt Staphylococcus aureus survival: clinical implications of recent discoveries

“…For example, LukAB is highly lytic to human phagocytes but only weakly toxic to murine cells due to species-specific differences in the LukAB receptor CD11b (60,63,64). Similarly, PVL and HlgCB do not bind murine C5aR1/2, the myeloid receptor for these toxins (65,66). The species-specific disparity in receptor binding has likely led to an underestimation of the importance of these toxins for human disease.…”

“…In particular, in emerging community-associated MRSA strains, PVL expression strongly correlates with necrotizing human diseases but is not required for pathologic phenotypes in mice (158). The long-standing controversy over the role of PVL in disease was unraveled after the discovery that PVL binds strongly to human, but not mouse, C5aR (66). The failed clinical trials of S. aureus component vaccines that were successfully developed in mice have also been unsettling (14) and have raised serious concerns regarding key differences between human and mouse immune responses to S. aureus.…”