JAC Advance Access originally published online on October 28, 2006
Journal of Antimicrobial Chemotherapy 2007 59(1):157-159; doi:10.1093/jac/dkl430
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Correspondence |
Comment on: Human intravenous immunoglobulin for experimental streptococcal toxic shock: bacterial clearance and modulation of inflammation
1 Department of Immunology, Mayo Clinic College of Medicine 200 First Street, SW, Rochester, MN 55905, USA 2 Divisions of Infectious Diseases and Clinical Microbiology, Mayo Clinic College of Medicine Rochester, MN 55905, USA 3 INSERM Unité 681 and Université Pierre et Marie Curie, Institut des Cordeliers Paris, France
*Corresponding author. Tel: +1-507-284-8180; Fax: +1-507-266-0981; E-mail: rajagopalan.govindarajan{at}mayo.edu
Keywords: superantigens , IVIg , HLA class II transgenic mice
Sir,
In a recent report, Sriskandan et al.,1 evaluated human intravenous immunoglobulin (IVIg) in streptococcal toxic shock using the HLA-DQ8 transgenic mouse model. They observed that human IVIg neutralized streptococcal superantigens in vitro as well as in vivo and concluded that human IVIg could have potential therapeutic benefit in streptococcal toxic shock syndrome.1 Using a similar system we have observed that IVIg did not neutralize purified streptococcal superantigen-induced lymphocyte proliferation in vitro as well as in vivo. While Sriskandan et al.1 used streptococcal bacterial culture supernatants as the source of bacterial superantigens, we used purified individual streptococcal bacterial superantigens for our study.
For in vitro studies, splenic mononuclear cells, collected from naive Aßo. HLA-DQ8 transgenic mice,2 were cultured with medium alone, indicated concentrations of superantigens or superantigen plus IVIg (1 mg/mL) for 48 h. Cell proliferation was determined by a standard thymidine incorporation assay. IL-2 and IFN-
present in the culture supernatant were quantified by sandwich ELISA. The following purified superantigens were used in vitro (Toxin Technology, Sarasota, FL, USA): streptococcal pyrogenic exotoxin (SPE) A, SPEB (not a superantigen, used as an internal control), SPEC, streptococcal mitogenic exotoxin (SME) Z2 (a gift from John D. Fraser, University of Auckland, New Zealand) and staphylococcal enterotoxin B (SEB). As sources of IVIg, we used several commercially available IVIg preparations including Tegeline (LFB, France), Octagam (Octapharma, Austria), Immunovenin (Bulgaria), Gammagard (Baxter) and Endobulin (Immuno, Austria). All experiments were approved by the Mayo Clinic Institutional Animal Care and Use Committee.
As shown in Figure 1(a), IVIg, even at a 1000- to 10 000-fold higher concentration than the superantigens, was not capable of abolishing superantigen-induced T cell proliferation and nor was it capable of suppressing superantigen-induced IL-2 and IFN- production in the culture supernatants (not shown).
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Next, we evaluated the ability of IVIg to neutralize superantigen activity in vivo. HLA-DQ8 transgenic mice were challenged with 10 µg of SPEA or SMEZ2 intraperitoneally followed by 1 g/kg of IVIg, also given intraperitoneally. PBS-challenged mice and experimental mice were sacrificed on day 3 and the distribution of CD4+ and CD8+ T cells expressing specific TCR Vß families was analysed by flow cytometry using commercial antibodies. As shown in Figure 1(b) (SPEA) and Figure 1(c) (SMEZ), administration of IVIg did not reduce the extent of superantigen-induced expansion of either CD4+ or CD8+ T cell subsets expressing specific TCR Vß families. SPEA predominantly stimulates T cells expressing TCR Vß8 but not TCR Vß6 or 11. Accordingly, HLA-DQ8 mice challenged with SPEA showed a significant increase in the TCR Vß8+ T cells in both CD4+ and CD8+ subsets. HLA-DQ8 transgenic mice challenged with SPEA and administered IVIg showed similar or even slightly higher expansion of TCR Vß8+ T cells in both CD4+ and CD8+ subsets, indicating that IVIg did not neutralize immune activation by SPEA. All IVIg preparations lacked suppressive activity against SPEA in vivo. The same was true for SMEZ2 which primarily activates T cells expressing TCR Vß11.
We have shown in previous studies that while systemic administration of bacterial superantigens causes expansion of peripheral mature T cells, it causes massive apoptosis of CD4CD8 double positive thymocytes in the thymus. We observed that administration of IVIg did not rescue superantigen-induced CD4CD8 double positive thymocyte apoptosis in vivo in HLA-DQ8 transgenic mice (data not shown). We have shown previously that HLA-DQ8 transgenic mice with targeted disruption of the IL-10 gene are extremely sensitive to bacterial superantigen-induced toxic shock and mortality.3 Mortality in DQ8.IL-10–/– mice challenged with superantigen alone was no different from the group challenged with superantigen along with IVIg treatment (SPEA alone, 2/2; SPEA+IVIg, 3/4; SEB alone, 4/4; SEB+IVIg, 3/3). We determined whether administration of IVIg prior to superantigen challenge would have any protective effect on superantigen-induced immune activation and mortality. For this, we first administered 1 g/kg of IVIg intraperitoneally in to HLA-DQ8 and HLA-DQ8.IL-10–/– mice, followed 30 min later by 10 µg of SPEA. The extent of T cell expansion was comparable between HLA-DQ8 transgenic pretreated with IVIg or not (data not shown). Similarly, the extent of mortality was similar in HLA-DQ8.IL-10–/– mice either pre-treated or not with IVIg (3/3 in each group).
We also screened the ability of IVIg to neutralize the staphylococcal superantigen, SEB using HLA-DR3 as well as HLA-DQ8 transgenic mice. IVIg did not show any significant neutralization of SEB activity in vitro (Figure 1a) or in vivo (data not shown), similar to our previous findings.4 Sriskandan et al.,1 also showed that IVIg preparations can have opsonizing activity which may help clear bacterial infection. However, our previous study indicated a lack of benefit of IVIg in a murine model of group A streptococcal necrotizing fasciitis.5
Bacterial superantigens generally have two modes of binding to MHC class II molecules; low affinity or generic binding and high affinity or zinc-dependent binding.6 To be effective, the natural antibodies present in IVIg should be of sufficiently high affinity to prevent high affinity interactions between extremely small amounts of bacterial superantigens and their abundantly present ligands, MHC class II molecules.6 Results of our studies differ from those of Sriskandan et al.1 The IVIg preparations we studied were different from the preparation studied by Sriskandan et al.1 (Endobulin S/D, Baxter) and it has been recently shown that the ability to neutralize various bacterial superantigens varies among different IVIg preparations.7 Alternatively, differences may relate to the use of purified superantigens versus bacterial culture supernatants.
Transparency declarations
GR, RP and CSD have none to declare. SVK has received grants in the last 3 years to study various aspects of the mechanisms of autoimmune and inflammatory diseases from LFB, ZLB Behring and Talecris Biotherapeutics.
Acknowledgements
We thank Julie Hanson and her crew for excellent mice husbandry. This study was supported by NIH grant AI14764.
References
1
Sriskandan S, Ferguson M, Elliot V, et al. (2006) Human intravenous immunoglobulin for experimental streptococcal toxic shock: bacterial clearance and modulation of inflammation. J Antimicrob Chemother 58:117–24.
2
Rajagopalan G, Smart MK, Krco CJ, et al. (2002) Expression and function of transgenic HLA-DQ molecules and lymphocyte development in mice lacking invariant chain. J Immunol 169:1774–83.
3
Rajagopalan G, Sen M, David CS. (2004) In vitro and in vivo evaluation of staphylococcal superantigen peptide antagonists. Infect Immun 72:6733–7.
4 Baudet V, Hurez V, Lapeyre C, et al. (1996) Intravenous immunoglobulin (IVIg) modulates the expansion of V beta 3+ and V beta 17+ T cells induced by staphylococcal enterotoxin B superantigen in vitro. Scand J Immunol 43:277–82.[ISI][Medline]
5 Patel R, Rouse MS, Florez MV, et al. (2000) Lack of benefit of intravenous immune globulin in a murine model of group A streptococcal necrotizing fasciitis. J Infect Dis 181:230–4.[CrossRef][ISI][Medline]
6 Sundberg EJ, Li Y, Mariuzza RA. (2002) So many ways of getting in the way: diversity in the molecular architecture of superantigen-dependent T-cell signaling complexes. Curr Opin Immunol 14:36–44.[CrossRef][ISI][Medline]
7 Schrage B, Duan G, Yang LP, et al. (2006) Different preparations of intravenous immunoglobulin vary in their efficacy to neutralize streptococcal superantigens: implications for treatment of streptococcal toxic shock syndrome. Clin Infect Dis 43:743–6.[CrossRef][ISI][Medline]
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