Laurie R. Hall

CXC Chemokine Receptor 2 But Not C-C Chemokine Receptor 1 Expression Is Essential for Neutrophil Recruitment to the Cornea in Helminth-Mediated Keratitis (River Blindness)

Infiltration of neutrophils and eosinophils into the mammalian cornea can result in loss of corneal clarity and severe visual impairment. To identify mediators of granulocyte recruitment to the corneal stroma, we determined the relative contribution of chemokine receptors CXC chemokine receptor (CXCR)-2 (IL-8R homologue) and CCR1 using a murine model of ocular onchocerciasis (river blindness) in which neutrophils and eosinophils migrate from peripheral vessels to the central cornea. CXCR2−/− and CCR1−/− mice were immunized s.c. and injected into the corneal stroma with Ags from the parasitic helminth Onchocerca volvulus. We found that production of macrophage-inflammatory protein (MIP)-2, KC, and MIP-1α was localized to the corneal stroma, rather than to the epithelium, which was consistent with the location of neutrophils in the cornea. CCR1 deficiency did not inhibit neutrophil or eosinophil infiltration to the cornea or development of corneal opacification. In marked contrast, neutrophil recruitment to the corneas of CXCR2−/− mice was significantly impaired (p < 0.0001 compared with control, BALB/c mice) with only occasional neutrophils detected in the central cornea. Furthermore, CXCR2−/− mice developed only mild corneal opacification compared with BALB/c mice. These differences were not due to impaired KC and MIP-2 production in the corneal stroma of CXCR2−/− mice, which was similar to BALB/c mice. Furthermore, although MIP-1α production was lower in CXCR2−/− mice than BALB/c mice, eosinophil recruitment to the cornea was not impaired. These observations demonstrate the critical role for CXCR2 expression in neutrophil infiltration to the cornea and may indicate a target for immune intervention in neutrophil-mediated corneal inflammation.

Immune mechanisms in Onchocerca volvulus-mediated corneal disease (river blindness).

Infection with the parasitic nematode Onchocerca volvulus can lead to severe visual impairment and blindness. In an effort to characterize the molecular basis for the inflammatory response in the cornea, we have developed a murine model for O. volvulus‐mediated keratitis in which parasite antigens are injected into the corneal stroma of sensitized mice. This model reproduces the two main clinical features of human disease, corneal opacification and neovascularization. Histological analysis of corneas from these mice reveals a biphasic recruitment of neutrophils and eosinophils to the central cornea, along with a small, but persistent number of CD3+ cells. In this review, we present evidence that production of antigen‐specific T cell and antibody responses are essential for development of O. volvulus keratitis, and we propose a sequence of molecular and cellular events that lead to migration of inflammatory cells to the cornea and to loss of corneal clarity.

A Dominant Role for Fcγ Receptors in Antibody-Dependent Corneal Inflammation

Although production of specific Ab is a critical element of host defense, the presence of Ab in tissues leads to formation of immune complexes, which can trigger a type III Arthus reaction. Our studies on a mouse model of river blindness showed that Ab production is essential for recruitment of neutrophils and eosinophils to the cornea and for development of corneal opacification. In the current study, we determined the relative contribution of complement and FcγR interactions in triggering immune complex-mediated corneal disease. FcγR−/− mice, C3−/− mice, and immunocompetent control (B6/129Sj) mice were immunized s.c. and injected intrastromally with Onchocerca volvulus Ags. Slit lamp examination showed that control mice, C3−/− mice, and control mice injected with cobra venom factor developed pronounced corneal opacification, whereas corneas of FcγR−/− mice remained completely clear. Furthermore, recruitment of neutrophils and eosinophils to the corneal stroma was significantly impaired in FcγR−/− mice, but not in C3−/− mice or cobra venom factor-treated mice. We therefore conclude that FcγR-mediated cell activation, rather than complement activation, is the dominant pathway of immune complex disease in the cornea. These findings demonstrate a novel role for FcγR interactions in mediating ocular inflammation.

Reciprocal immunomodulatory effects of gamma interferon and interleukin-4 on filaria-induced airway hyperresponsiveness

ABSTRACT Tropical pulmonary eosinophilia (TPE) is a severe asthmatic syndrome of lymphatic filariasis, in which an allergic response is induced to microfilariae (Mf) in the lungs. Previously, in a murine model for TPE, we have demonstrated that recombinant interleukin-12 (IL-12) suppresses pulmonary eosinophilia and airway hyperresponsiveness (AHR) by modulating the T helper (Th) response in the lungs from Th2- to Th1-like, with elevated gamma-interferon (IFN-γ) production and decreased IL-4 and IL-5 production. The present study examined the immunomodulatory roles of IL-4 and IFN-γ in filaria-induced AHR and pulmonary inflammation using mice genetically deficient in these cytokines. C57BL/6, IL-4 gene knockout (IL-4−/−), and IFN-γ−/− mice were first immunized with soluble Brugia malayi antigens and then inoculated intravenously with 200,000 live Mf. Compared with C57BL/6 mice, IL-4−/− mice exhibited significantly reduced AHR, whereas IFN-γ−/− mice had increased AHR. Histopathologically, each mouse strain showed increased cellular infiltration into the lung parenchyma and bronchoalveolar space compared with naı̈ve animals. However, consistent with changes in AHR, IL-4−/− mice had less inflammation than C57BL/6 mice, whereas IFN-γ−/− mice had exacerbated pulmonary inflammation with the loss of pulmonary architecture. Systemically, IL-4−/− mice produced significantly higher IFN-γ levels compared with C57BL/6 mice, whereas IFN-γ−/− mice produced significantly higher IL-4 levels. These data indicate that IL-4 is required for the induction of filaria-induced AHR, whereas IFN-γ suppresses AHR.

CD4(+) depletion selectively inhibits eosinophil recruitment to the cornea and abrogates Onchocerca volvulus keratitis (River blindness).

ABSTRACT Previous studies demonstrated that in the murine model ofOnchocerca volvulus keratitis, neutrophils and eosinophils are recruited into the cornea in a biphasic manner in response to intrastromal injection. To determine if CD4+ T cells regulate migration of neutrophils and eosinophils into the cornea, CD4+ cells were depleted using monoclonal antibody GK1.5 before intrastromal injection of parasite antigens. Depletion of CD4+ cells abrogated corneal opacification at later but not early stages of disease. Consistent with this observation, CD4 depletion significantly impaired recruitment of eosinophils to the cornea but had no effect on neutrophils. These data indicate that CD4+ T cells mediate sustained O. volvuluskeratitis by regulating eosinophil recruitment to the cornea.

Interleukin-12 suppresses filaria-induced pulmonary eosinophilia, deposition of major basic protein and airway hyperresponsiveness

Tropical Pulmonary Eosinophilia (TPE) is a severe form of allergic asthma caused by the host inflammatory response to filarial helminths in the lung microvasculature, and is characterized by pulmonary eosinophilia, increased filarial‐specific IgG and IgE antibodies, and airway hyperresponsiveness. The current study examined the effect of IL‐12 on pulmonary eosinophilia, deposition of eosinophil major basic protein and airway hyperresponsiveness in mice inoculated i.v. with Brugia malayi microfilariae. Injection of recombinant murine IL‐12 modulated the T helper (Th) response in the lungs from Th2‐ to Th1‐like, with elevated IFN‐γ, and decreased IL‐4 and IL‐5 production. Consistent with this shift in cytokine response, antigen‐specific IgG2a was elevated, and IgG1 and total serum IgE were decreased. In addition, eosinophils in BAL fluid from IL‐12 treated mice were reduced from 56% to 11%, and there was no detectable MBP on respiratory epithelial cells. Importantly, IL‐12 suppressed airway hyperresponsiveness compared with saline‐injected control animals. Taken together, these data clearly demonstrate that by modulating Th associated cytokine production, IL‐12 down‐regulates filaria‐induced lung immunopathology.

Onchocerca volvulus keratitis (river blindness) is exacerbated in BALB/c IL-4 gene knockout mice

To determine the outcome of Onchocerca volvulus keratitis in IL-4(-/-) BALB/c mice, animals were immunized subcutaneously and injected into the corneal stroma with soluble O. volvulus antigens. IL-4(-/-) BALB/c mice had a deviated cellular response, with decreased serum IgE and IgG1 and elevated IgG2a compared with control BALB/c mice. In marked contrast to control BALB/c, C57BL/6, and IL-4(-/-) C57BL/6 mice, IL-4(-/-) BALB/c mice developed severe corneal opacification and neovascularization that was associated with a pronounced neutrophil infiltrate to the corneal stroma. STAT-6(-/-) BALB/c mice had the same phenotype as IL-4(-/-) BALB/c mice, and complement depletion had no effect on the severity of O. volvulus keratitis in these mice. These findings indicate that on a BALB/c background, IL-4 has a critical role in regulating neutrophil recruitment to the cornea and development of O. volvulus keratitis.

Cytokine Regulation of Filaria: Induced Airway and Corneal Disease

Approximately 200 million individuals are infected with filarial helminths, the parasitic helminths that cause lymphatic filariasis and onchocerciasis (river blindness). Filariae are thread-like nematodes that are transmitted by the bite of blood-sucking arthropods (mosquitoes transmit lymphatic filariae and black flies transmit onchocerciasis). Adult males and females are viviparous, and the early first stage larvae, termed microfiariae, are present in either the blood (lymphatic filariae) or the skin (onchocerciasis).