MHC Class II Activation and Interferon-γ Mediate the Inhibition of Neutrophils and Eosinophils by Staphylococcal Enterotoxin Type A (SEA).

Anelize S. Pinheiro-Torres,Antônio Condino-Neto,Ana P. Ferreira-Duarte,Gabriel F. Anhê,Edson Antunes,Ivani A. DeSouza

doi:10.3389/fcimb.2017.00518

Abstract

Staphylococcal enterotoxins are classified as superantigens that act by linking T-cell receptor with MHC class II molecules, which are expressed on classical antigen-presenting cells (APC). Evidence shows that MHC class II is also expressed in neutrophils and eosinophils. This study aimed to investigate the role of MHC class II and IFN-γ on chemotactic and adhesion properties of neutrophils and eosinophils after incubation with SEA. Bone marrow (BM) cells obtained from BALB/c mice were resuspended in culture medium, and incubated with SEA (3–30 ng/ml; 1–4 h), after which chemotaxis and adhesion were evaluated. Incubation with SEA significantly reduced the chemotactic and adhesive responses in BM neutrophils activated with IL-8 (200 ng/ml). Likewise, SEA significantly reduced the chemotactic and adhesive responses of BM eosinophils activated with eotaxin (300 ng/ml). The inhibitory effects of SEA on cell chemotaxis and adhesion were fully prevented by prior incubation with an anti-MHC class II blocking antibody (2 μg/ml). SEA also significantly reduced the intracellular Ca2+ levels in IL-8- and eotaxin-activated BM cells. No alterations of MAC-1, VLA4, and LFA-1α expressions were observed after SEA incubation. In addition, SEA elevated by 3.5-fold (P < 0.05) the INF-γ levels in BM cells. Incubation of BM leukocytes with IFN-γ (10 ng/ml, 2 h) reduced both neutrophil and eosinophil chemotaxis and adhesion, which were prevented by prior incubation with anti-MHC class II antibody (2 μg/ml). In conclusion, SEA inhibits neutrophil and eosinophil by MHC class II-dependent mechanism, which may be modulated by concomitant release of IFN-γ.

Highlights

Staphylococcus aureus is one of the most important human pathogen associated with severe hospital-acquired infections, including pneumonia, endocarditis, and sepsis (Adhikari et al, 2012; Nair et al, 2014)
Activation of bone marrow (BM) neutrophils with IL-8 (200 ng/ml) markedly enhanced the cell adhesion on both VCAM1 and intercellular adhesion molecule 1 (ICAM-1) pre-coated plates in comparison with non-stimulated cells (P < 0.05; Figures 1A–D)
Our present study demonstrates that Staphylococcal enterotoxin types A (SEA) markedly reduces the in vitro chemotactic and adhesive responses of activated BM neutrophils and eosinophils, an effect associated with reduced intracellular Ca2+ levels

Summary

Introduction

Staphylococcus aureus is one of the most important human pathogen associated with severe hospital-acquired infections, including pneumonia, endocarditis, and sepsis (Adhikari et al, 2012; Nair et al, 2014). Staphylococcus aureus infections have been strongly associated to its ability to produce several virulent factors such as adhesins, collagenases, protein A, coagulases, hemolysins, SEA Inhibits Granulocyte Functional Properties and leukocidins (Krakauer and Stiles, 2013). Staphylococcal enterotoxins are superantigens due its properties to induce extensive proliferation of T cells mediated by cross-linking of the variable region of the β chain of the T-cell receptor (TCR) with MHC class II molecules on antigenpresenting cells (APC) such as macrophages and dendritic cells (Fraser, 2011). Human and murine neutrophils (Ostanin et al, 2012; Pliyev et al, 2014) and eosinophils express MHC Class II (Wang et al, 2007; Farhan et al, 2016), but little is known about the role of this glycoprotein in these granulocytes

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