Contribution of Each of Four Superantigens toStreptococcus equi-Induced Mitogenicity, Gamma Interferon Synthesis, and Immunity

Abstract

Streptococcus equi is the causative agent of strangles, the most frequently diagnosed infectious disease of horses worldwide. The disease is characterized by abscessation and swelling of the lymph nodes of the head and neck, which can literally strangle the horse to death. S. equi produces four recently acquired phage-associated bacterial superantigens (sAgs; SeeH, SeeI, SeeL, and SeeM) that share homology with the mitogenic toxins of Streptococcus pyogenes. The aim of this study was to characterize the contribution of each of these S. equi sAgs to mitogenic activity in vitro and quantify the sAg-neutralizing capacity of sera from naturally infected horses in order to better understand their role in pathogenicity. Each of the sAgs was successfully cloned, and soluble proteins were produced in Escherichia coli. SeeI, SeeL, and SeeM induced a dose-dependent proliferative response in equine CD4 T lymphocytes and synthesis of gamma interferon (IFN-␥). SeeH did not stimulate equine peripheral blood mononuclear cells (PBMC) but induced proliferation of asinine PBMC. Allelic replacement mutants of S. equi strain 4047 with sequential deletion of the superantigen genes were generated. Deletion of seeI, seeL, and seeM completely abrogated the mitogenic activity and synthesis of IFN-␥, in equine PBMC, of the strain 4047 culture supernatant. Sera from naturally infected convalescent horses had only limited sAg-neutralizing activities. We propose that S. equi sAgs play an important role in S. equi pathogenicity by stimulating an overzealous and inappropriate Th1 response that may interfere with the development of an effective immune response.

Exacerbated Type II Interferon Response Drives Hypervirulence and Toxic Shock by an Emergent Epidemic Strain of Streptococcus suis

“…Gene gain via the horizontal acquisition of mobile genetic elements is a key factor in the emergence of new pathogenic strains of streptococci. For example, acquisition of superantigen-encoding genes by S. pyogenes has been associated with increased morbidity and mortality in humans (39,40). The emergence of a new, epidemic ST of S. suis during the Chinese outbreak leading to unusual clinical manifestations related to STSLS allowed the hypothesis of the acquisition of superantigens by this important zoonotic pathogen to arise as well.…”

Identification of Three Novel Superantigen-Encoding Genes in Streptococcus equi subsp. zooepidemicus , szeF , szeN , and szeP

“…equi did not stimulate equine PBMCs in vitro and that deletion of seeI, seeL, and seeM abolished the mitogenic activity of S. equi subsp. equi strain 4047 culture supernatants (33). SeeH was found to stimulate PBMCs isolated from 6 out of 8 donkeys and is hypothesized to increase the ability of S. equi subsp.…”

“…Functional activities of S. equi subsp. zooepidemicus sAgs were measured as previously described (33). Briefly, equine peripheral blood mononuclear cells (PBMCs) were purified from heparinized blood by centrifugation on a Ficoll density gradient.…”

“…equi sAgs stimulate equine T-cell proliferation in vitro and likely play an important role in S. equi subsp. equi pathogenicity (2,4,33). Interestingly, S. equi subsp.…”

Streptococcus equi: a pathogen restricted to one host

“…These data suggest that SLS plays a role in S. equi virulence, but indicate that other factors are also important to the ability of this organism to cause disease. Two other prophage of S. equi strain 4047 encode four bacterial sAgs -SeeL and SeeM encoded on QSeq3, and SeeH and SeeI encoded on QSeq4, which share homology with the mitogenic toxins of S. pyogenes Paillot et al, 2010b;. sAgs are potent immuno-stimulatory molecules that disrupt innate and adaptive immune responses through non-specific T lymphocyte proliferation and the generation of an overzealous pro-inflammatory response (Llewelyn & Cohen, 2002;Sriskandan et al, 2007).…”