Systemic immunity in herpetic keratitis

Expression of herpes virus entry mediator (HVEM) in the cornea and trigeminal ganglia of normal and HSV-1 infected mice

PURPOSE

Herpes virus entry mediator (HVEM) plays a critical role in the regulation of inflammation through interaction with its natural ligands LIGHT and lymphotoxin alpha and also serves as one of the entry receptors of herpes simplex virus (HSV). The purpose of this study was to better understand the expression of HVEM in the cornea and trigeminal ganglia (TG), which are important targets of HSV infection.

MATERIALS AND METHODS

Immunohistochemistry was used to define HVEM expression in the cornea and TG of normal and HSV-1 infected mice euthanized 2 to 5 days or 7 months following corneal inoculation of virus.

RESULTS

We found that HVEM is widely expressed in the normal corneal epithelium and endothelium, is weakly and focally expressed in the corneal stroma, and is expressed in a portion of neurons and non-neuronal cells in the TG. Acute HSV-1 keratitis and ganglionitis were associated with increased HVEM expression in the corneal epithelium and stroma and in neurons and non-neuronal cells of TG, and many inflammatory cells in these tissues also expressed HVEM. TG derived from mice 7 months after virus inoculation demonstrated latent HSV-1 infection that was associated with increased HVEM expression in neurons and non-neuronal cells relative to uninfected control tissues. Latent TG also contained focal infiltrates of mononuclear inflammatory cells, many of which expressed HVEM. Corneas derived from latently infected mice demonstrated chronic keratitis, with no evidence of virus replication or increased HVEM expression in the corneal epithelium, and inflammatory cells present showed only weak HVEM expression.

CONCLUSIONS

HVEM is expressed in the cornea and TG and therefore may serve as an HSV entry receptor in these tissues. Furthermore, these findings raise the possibility that changes in HVEM expression following ocular HSV-1 infection can modulate HSV spread and infection-induced inflammation in the cornea and TG.

Comparative study of ocular herpes simplex virus in patients with and without self-reported atopy

PURPOSE

To compare the characteristics of ocular herpes simplex virus (HSV) in patients with and without atopy.

DESIGN

Retrospective cohort comparative study.

METHODS

Patients who presented at the Cornea Service, Wills Eye Hospital, between March 2003 and March 2004 who had been previously diagnosed in the same institution as having ocular HSV diagnosis or were just diagnosed as having the disease were asked to complete a study questionnaire that enabled categorization into atopic and nonatopic. In April 2005, 223 patients who agreed to be in the study had their charts reviewed, and 125 patients were excluded according to exclusion criteria: immunosuppression, follow-up less than one year, previous history of penetrating keratoplasty (PK) out of the Cornea Service, and no active HSV episode during follow-up.

MAIN OUTCOME MEASURES

Incidence of all types of HSV recurrences.

SECONDARY OUTCOME MEASURES

Bilaterality, visual loss, need for PK , and secondary bacterial infection in both groups. HSV episodes were classified into infectious, inflammatory, and mixed for analysis.

RESULTS

Ninety eight patients (110 eyes) were included in the study. Atopic/nonatopic (P value): the mean follow-up was 11.6 (+/- 10.6)/8.8 years (+/- 8.4) (P = .14); the mean incidence of HSV episodes per year of follow-up was: total episodes 0.32 (+/- 0.36)/0.28 (+/- 0.33) (P = .14), infectious 0.16 (+/- 0.22)/0.10 (+/- 0.14) (P < .01), inflammatory 0.11 (+/- 0.19)/0.11 (+/- 0.19) (P < .01), and mixed 0.09 (+/- 0.20)/0.07 (+/- 0.16) (P = .06); bilateral HSV was present in 9/3 patients (P = .22); the mean loss of vision was four lines of Snellen in both groups; PK was performed in 14 of 16 eyes (P = .45); secondary bacterial infection was present in two of four eyes (P = .26).

CONCLUSIONS

Atopic patients had considerably more infectious and fewer inflammatory episodes when compared with nonatopics.

Cell mediated immunity in herpes simplex keratitis in man

Varied manifestations of herpes simplex keratitis are postulated to be related to alterations or paucity of protective immune response to the virus. In this study lymphocyte subpopulations and macrophage inhibition factor (MIF) assay are investigated in herpes simplex keratitis. Active T-lymphocytes are detected to be significantly low in active keratitis as compared to the healed stage (P less than 0.001) and normal control subjects (P less than 0.01). Active T-cells are also lower in bilateral keratitis than in unilateral keratitis (P less than 0.01), and in stromal keratitis than in epithelial keratitis (P less than 0.05). Total E-rosette-forming cells and leucocyte migration inhibition factor (MIF) assay demonstrates significantly lower values in bilateral keratitis than in unilateral keratitis, and in stromal keratitis than in epithelial keratitis. On healing, total E-RFC, active T-cells and MIF values improved and are comparable to those found in normal subjects. Enumeration of absolute lymphocyte counts and EAC rosette-forming cells (B-lymphocyte cells) did not yield any differences. Our observations demonstrate paucity of cell-mediated immune response in stromal keratitis. More marked deficiency is demonstrable in bilateral keratitis. Manifestations of herpes simplex keratitis and their healing is observed to be relatable to the level of cell mediated immune response.

Arachidonic acid cascade and platelet-activating factor in the network of eye inflammatory mediators: therapeutic implications in uveitis

The cellular and biochemical events triggered by uveitis involve a complex array of cells and a heterogeneous network of mediators of intraocular inflammation. Resident cells are activated and inflammatory cells are recruited. Chemical mediators from the arachidonic acid cascade, prostaglandins, hydroxyeicosatetraenoic acids, and leukotrienes, are formed. Several of these metabolites are modulators of cellular functions, but when generated in sustained, excessive amounts, they contribute to enhanced vascular permeability and to the onset of pathophysiological responses. Another very active membrane-derived mediator is platelet-activating factor. This important mediator of immune and inflammatory responses may play a central role in uveitis due to cell priming, since interleukin-1, tumor necrosis factor, and other as yet unidentified mediators are also being generated. The concomitant accumulation of these networks of mediators in various parts of the uveal tract leads to spreading of the intraocular inflammatory response and cellular damage. At both early and late stages of uveitis, the generation of free radicals is also a major contributor to the impairment of function. Free radicals are generated in two distinct sites: in the oxidative burst of recruited white cells and in free radical formation and lipid peroxidation in resident cells. The identification of the cellular events that lead to the accumulation of networks of mediators of inflammation and their effects has important therapeutic implications in uveitis.

Management and prevention of ocular viral and chlamydial infections

A majority of cases of preventable and/or curable ocular morbidity and blindness are caused by ocular infections. They may account for 70 to 90% of all ocular morbidity seen by family doctors, general practitioners, health centers, and local ophthalmologists in both developed and developing countries. Unfortunately, most health authorities and doctors, including ophthalmologists, consider these diseases to be of little or no importance because they are not fully aware of the high prevalence of these infections and the blinding sequelae which may occur following incorrect diagnosis and treatment. Also, they are not aware of the social and economic impact of these infections in the absence of proper management and implementation of preventive measures. In this review, we examine present knowledge of chlamydial and common viral ocular infections. We discuss the problems of diagnosis, management, and prevention and propose solutions relevant to developed and developing countries.

Activity of rabbit monocytes, macrophages, and neutrophils in antibody-dependent cellular cytotoxicity of herpes simplex virus-infected corneal cells

Rabbit phagocytes were examined for their ability to kill target cells infected with herpes simplex virus by antibody-dependent cellular cytotoxicity. Two sources of rabbit corneal cells were used as targets: Staaten Seruminstitut Rabbit Cornea (a continuous cell line) and stromal keratocytes from the middle layer of corneas excised from New Zealand white rabbits. Peritoneal exudate and alveolar macrophages were found to be the most active effector cells, followed by blood neutrophils and monocytes. Peritoneal exudate and alveolar macrophages killed target cells with dilutions of antibody as high as 1:10,000. Monocyte antibody-dependent cellular cytotoxicity activity was absent in over one-third of the rabbits tested and was only weakly active in positive rabbits. In vitro aging of monocytes did not enhance activity. Antibody reactive with peritoneal exudate macrophages, alveolar macrophages, and blood neutrophil effector cells appeared 7 days after intracorneal injection of infectious herpes simplex virus. Results of these studies show that in vitro assays with a complete rabbit system (effectors cells, antibody, and target cells) can be developed to monitor herpetic disease and suggest an active role for rabbit phagocytes in cytotoxicity of herpes simplex virus-infected cells.

Experimental ulcerative herpetic keratitis. I. Systemic immune responses and resistance to corneal infection

The influence of previous infection with herpes simplex virus (HSV) on the susceptibility of rabbits to corneal inoculation of the virus was studied by means of the microtitration model for ulcerative herpetic keratitis. Systemic immune responses were assayed after skin and eye infections by means of the lymphocyte transformation (LT) and complement fixation (CF) tests. Both cutaneous and ocular primary infections resulted in cellular and humoral immune responses to HSV. In comparison to primary ocular infection, corneal disease in rabbits with previous skin infection ('secondary corneal infection') resulted in earlier initiation of cellular and humoral immune responses, while complement-fixing antibody titres reached a higher level. A previous cutaneous infection ('immunisation') provided considerable protection to the cornea and also accelerated recovery from corneal ulcerative disease. A correlation was observed between the initiation of the lymphocyte transformation response and the beginning of healing of corneal ulceration. A previous unilateral ocular infection induced an even higher degree of corneal resistance in that eye, and the opposite eye was protected to the same extent as by cutaneous immunisation.