Passively Administered Pooled Human Immunoglobulins Exert IL-10 Dependent Anti-Inflammatory Effects that Protect against Fatal HSV Encephalitis

Abstract

HSV-1 is the leading cause of sporadic encephalitis in humans. HSV infection of susceptible 129S6 mice results in fatal encephalitis (HSE) caused by massive inflammatory brainstem lesions comprising monocytes and neutrophils. During infection with pathogenic microorganisms or autoimmune disease, IgGs induce proinflammatory responses and recruit innate effector cells. In contrast, high dose intravenous immunoglobulins (IVIG) are an effective treatment for various autoimmune and inflammatory diseases because of potent anti-inflammatory effects stemming in part from sialylated IgGs (sIgG) present at 1–3% in IVIG. We investigated the ability of IVIG to prevent fatal HSE when given 24 h post infection. We discovered a novel anti-inflammatory pathway mediated by low-dose IVIG that protected 129S6 mice from fatal HSE by modulating CNS inflammation independently of HSV specific antibodies or sIgG. IVIG suppressed CNS infiltration by pathogenic CD11b+ Ly6Chigh monocytes and inhibited their spontaneous degranulation in vitro. FcγRIIb expression was required for IVIG mediated suppression of CNS infiltration by CD45+ Ly6Clow monocytes but not for inhibiting development of Ly6Chigh monocytes. IVIG increased accumulation of T cells in the CNS, and the non-sIgG fraction induced a dramatic expansion of FoxP3+ CD4+ T regulatory cells (Tregs) and FoxP3− ICOS+ CD4+ T cells in peripheral lymphoid organs. Tregs purified from HSV infected IVIG treated, but not control, mice protected adoptively transferred mice from fatal HSE. IL-10, produced by the ICOS+ CD4+ T cells that accumulated in the CNS of IVIG treated, but not control mice, was essential for induction of protective anti-inflammatory responses. Our results significantly enhance understanding of IVIG's anti-inflammatory and immunomodulatory capabilities by revealing a novel sIgG independent anti-inflammatory pathway responsible for induction of regulatory T cells that secrete the immunosuppressive cytokine IL-10 and further reveal the therapeutic potential of IVIG for treating viral induced inflammatory diseases.

Anti-inflammatory activity of intravenous immunoglobulins protects against West Nile virus encephalitis

“…Importantly, IVIG lacking E-gp-specific antibodies still conferred significant protection, which showed that virus neutralization was not the main mechanism by which IVIG protected against WNV encephalitis. These findings extend our experience with IVIG protection against HSV1 encephalitis (Ramakrishna et al, 2011), and support the use of IVIG as an effective immunotherapeutic for treatment of suspected cases of WNV and HSV1 encephalitis.…”

“…1c) despite being incapable of neutralizing virus infectivity (Table 1). This result showed that WNV neutralizing activity of IVIG was not critical for protection from WNV encephalitis and that alternative mechanisms could mediate protection (Vogt et al, 2011), which we anticipated based on our demonstration that IVIG protection against HSV1 encephalitis was independent of neutralizing antibodies (Ramakrishna et al, 2011).…”

“…IVIG has a broad repertoire of neutralizing antibodies for various pathogens and neutralization is commonly assumed to be the mechanism of protection against viral infection. However, we have shown in the HSV1 model that IVIG devoid of neutralizing antibodies is as effective as IVIG in protection against encephalitis (Ramakrishna et al, 2011) and the reports that non-neutralizing antibodies can protect against WNV infection are consistent with this (Chung et al, 2006;Mehlhop et al, 2005;Vogt et al, 2011). Studies investigating IVIG protection from WNV infection have based dosing on its neutralizing activity and have thus used IVIG at suboptimal doses (0.1-0.6 g kg 21 ) to elicit antiinflammatory responses.…”

“…This finding suggested that optimal treatment of WNV encephalitis required both antiviral and anti-inflammatory modalities. We previously showed that IVIG could temper CNS infiltration by pathogenic Ly6C high monocytes and Ly6G + neutrophils, and thereby protect mice from lethal HSV1 encephalitis (Ramakrishna et al, 2011). Additionally, earlier studies showed that high titrated IVIG collected from WNV endemic areas, but not non-immune IVIG, was protective in mouse WNV challenge studies when given at low doses (0.1-0.6 g kg 21 ) (Ben-Nathan et al, 2009;.…”

“…We found that a single dose of IVIG or WNV convalescent sera (WNV-IVIG) protected all mice from lethal WNV encephalitis when administered 24 h p.i. IVIG suppressed CNS infiltration by inflammatory cells, particularly the pathogenic Ly6C high CD11b + monocytes and CD11c + TNF + inducible nitric oxide synthase producing (Tip) DCs (Getts et al, 2008;King et al, 2011;Ramakrishna et al, 2011;Terry et al, 2012). Importantly, IVIG lacking E-gp-specific antibodies still conferred significant protection, which showed that virus neutralization was not the main mechanism by which IVIG protected against WNV encephalitis.…”