Association between mast cells and the development of experimental autoimmune uveitis in different rat strains

Ocular mast cells and mediators

Mast cells have long been recognized for their role in immediate hypersensitivity reactions, by virtue of the presence of high affinity receptors for IgE (FcepsilonRI) on their surface. More recently, mast cells have been postulated to be involved in a variety of chronic inflammatory disorders as numerous mediators released by activated mast cells are characterized. This article summarizes current information on mast cell mediators, heterogeneity, and differentiation, and it reviews studies of mast cells in the normal eye and various ocular disorders.

Basic pathogenic mechanisms operating in experimental models of acute anterior uveitis

Acute anterior uveitis is a recurrent inflammatory disease of the eye that occurs commonly, is distressing for the patient, and may have potentially blinding sequelae. The pathogenesis of the disease is poorly understood, and anti-inflammatory treatment is consequently non-specific and may be associated with significant complications. Animal models are a possible key to a better understanding of this disease. In one model, rats and mice develop a relatively short-lived anterior uveal inflammation almost immediately after systemic injection of bacterial endotoxin. Accumulating evidence suggests that cytokine production by resident uveal macrophages initiates endotoxin-induced uveitis which is characterized by an infiltration of neutrophils and mononuclear cells. A second model displays features in keeping with a delayed-type hypersensitivity immune response. Experimental melanin-induced uveitis is an acute recurrent uveitis with delayed onset but extended duration, observed when rats are immunized with bovine ocular melanin. Both animal models have clinical features in common with acute anterior uveitis, although experimental melanin-induced uveitis appears to mimic the human disease more closely. Novel treatment options to target implicated inflammatory cells and molecules are currently under consideration.

Strain differences in histamine release from peritoneal mast cells in rats

1. Peritoneal mast cells from Brown-Norway (BN) rats were compared with those from Wistar and Sprague-Dawley (SD) rats. 2. Peritoneal mast cells from BN rats showed the smallest values in number, cell diameter and histamine contents compared with those from Wistar and SD rats. 3. BN rat peritoneal mast cells were more sensitive to compound 48/80 and anti-IgE than were those from Wistar and SD rats, and they showed a higher response to A23187 than did cells from Wistar rats. 4. The histamine release from passively sensitized peritoneal mast cells was weaker in BN rats than was that from Wistar and SD rats.

The distribution of immune cells in the uveal tract of the normal eye

Inflammatory and immune-mediated diseases of the eye are not purely the consequence of infiltrating inflammatory cells but may be initiated or propagated by immune cells which are resident or trafficking through the normal eye. The uveal tract in particular is the major site of many such cells, including resident tissue macrophages, dendritic cells and mast cells. This review considers the distribution and location of these and other cells in the iris, ciliary body and choroid in the normal eye. The uveal tract contains rich networks of both resident macrophages and MHC class II+ dendritic cells. The latter appear strategically located to act as sentinels for capturing and sampling blood-borne and intraocular antigens. Large numbers of mast cells are present in the choroid of most species but are virtually absent from the anterior uvea in many laboratory animals; however, the human iris does contain mast cells. Small numbers of what are presumed to be trafficking lymphocytes are present in the uveal tract of normal eyes. There is little data available on the presence or absence of eosinophils. The role of these various cell types in immune homeostasis and ocular inflammation is briefly considered.

Murine autoimmune exocrinopathy: the minor salivary gland network shows a dichotomous pattern of histopathologic involvement

The minor salivary gland network of the MRL/l mouse was investigated in a kinetic study and compared with the major submandibular gland. We report that minor salivary glands adopt two mutually exclusive patterns of inflammatory lesions depending on the gland. The first pattern is characteristic of human Sjogren's syndrome. It developed during the second month, affected 89% of the animals over 20 weeks old, and consisted of an accumulation of mononuclear cells around the duct system. Only the anterior buccal gland (ABG) showed this pattern, which is shared by the major salivary glands. The ratio of CD4+ to CD8+ cells was the same in lesions and in healthy tissue. No neutrophils were found in these lesions. The second pattern affected all the minor salivary glands except the ABG. These lesions were never observed before the age of 20 weeks and affected 38% of MRL/l mice between the ages of 10-32 weeks. In this pattern, neutrophils were frequently found, but mainly gathered at the periphery of the gland lobules. That a systemic immunoregulatory defect may be expressed as two different patterns of histopathology in the minor salivary glands suggest that the network behaves as a dichotomous entity depending on particular microenvironmental influences.