Absence of Macrophage Inflammatory Protein-1α Prevents the Development of Blinding Herpes Stromal Keratitis

Abstract

Prior studies in our laboratory have suggested that the CC chemokine macrophage inflammatory protein-1α (MIP-1α) may be an important mediator in the blinding ocular inflammation which develops following herpes simplex virus type 1 (HSV-1) infection of the murine cornea. To directly test this hypothesis, MIP-1α-deficient (−/−) mice and their wild-type (+/+) counterparts were infected topically on the scarified cornea with 2.5 × 105 PFU of HSV-1 strain RE and subsequently graded for corneal opacity. Four weeks postinfection (p.i.), the mean corneal opacity score of −/− mice was 1.1 ± 0.3 while that of the +/+ mice was 3.7 ± 0.5. No detectable infiltrating CD4+ T cells were seen histologically at 14 or 21 days p.i. in −/− animals, whereas the mean CD4+ T-cell count per field (36 fields counted) in +/+ hosts was 26 ± 2 (P < 0.001). In addition, neutrophil counts in the −/− mouse corneas were reduced by >80% in comparison to the wild-type controls. At 2 weeks p.i., no interleukin-2 or gamma interferon could be detected in six of seven −/− mice, whereas both T-cell cytokines were readily demonstrable in +/+ mouse corneas. Also, MIP-2 and monocyte chemoattractant protein-1 protein levels were significantly lower in MIP-1α −/− mouse corneas than in +/+ host corneas, suggesting that MIP-1α directly, or more likely indirectly, influences the expression of other chemokines. Interestingly, despite the paucity of infiltrating cells, HSV-1 clearance from the eyes of −/− mice was not significantly different from that observed in +/+ hosts. We conclude that MIP-1α is not needed to control virus growth in the cornea but is essential for the development of severe stromal keratitis.

Ocular Tropism of Respiratory Viruses

“…Similarities in the elicitation of host responses to influenza virus, RSV, and adenovirus infection of corneal and conjunctival epithelial cells, notably with regard to the induction of the NF-B pathway, provide insight into potential shared mechanisms of inflammation following virus infection (55)(56)(57)196). While the mammalian species used to model ocular infection differ somewhat between viruses, shared protocols for virus inoculation, tissue harvesting, and sample manipulation underscore the ability to use advances from research with other respiratory pathogens with ocular complications or with pathogens such as herpes simplex virus, for which abundant data using a murine model are available, as a resource when further building on existing and nascent in vitro and in vivo ocular models of virus infection (80,197,198).…”

“…While host restrictions limit the permissiveness of some viruses to select species, these models have nonetheless provided valuable information (Table 2). Mouse models, used extensively to study herpesvirus keratitis, have further been adapted to study ocular complications from numerous viral respiratory diseases (27,66,71,80). The rabbit has long been used for the assessment of eye irritation and has since been utilized to study ocular disease following respiratory virus infection (65,73,81).…”

Viral Infection of the Lungs through the Eye

“…A similarly diluted sucrose solution was used in sham-infected control mice. We followed the inoculation procedure optimized for other ocular pathogens such as herpes simplex virus (HSV) (42), which results in a consistent infection without causing "blepharitis" (eyelid inflammation). In brief, mice were anesthetized by intraperitoneal injection of pentobarbital (50 mg/kg), and the right eye was lightly scarified by two twists of a 2-mm corneal trephine.…”

“…The chemokines are subdivided into four groups (CXC, CX 3 C, CC, and C) according to the positioning of the first two closely paired and highly conserved Cys residues of their amino acid sequences (36). The CC chemokines, generally involved in inflammation through monocyte-macro-phage activation and recruitment, play particularly important roles in the pathology of the RSV-infected lung and in various ocular diseases and infections (23,28,41,42,44). The clinical benefit stems from the discovery of proteins, antibodies, and small-molecule antagonists that inhibit chemokine activities and thereby reduce allergy and inflammation (1,15,39,42).…”

“…The CC chemokines, generally involved in inflammation through monocyte-macro-phage activation and recruitment, play particularly important roles in the pathology of the RSV-infected lung and in various ocular diseases and infections (23,28,41,42,44). The clinical benefit stems from the discovery of proteins, antibodies, and small-molecule antagonists that inhibit chemokine activities and thereby reduce allergy and inflammation (1,15,39,42). We reasoned that development of a rational intervention for the ocular pathology may benefit from an understanding of the cytokines response activated in the RSV-infected eye, which is currently unknown.…”