Expression of HLA antigens on the human uvea

Acute anterior uveitis and HLA-B27

Acute anterior uveitis is the most common form of uveitis. HLA-B27-associated acute anterior uveitis is a distinct clinical entity that has wide-ranging medical significance due to its ocular, systemic, immunologic, and genetic features. The association between HLA-B27 and the spectrum of HLA-B27-associated inflammatory diseases remains one of the strongest HLA-disease associations known to date. This review examines acute anterior uveitis with particular focus on HLA-B27-associated acute anterior uveitis, including the epidemiology, immunopathology, association with HLA-B27 and its subtypes, clinical features, complications, prognosis, and potential new therapies such as anti-TNFalpha therapy and oral HLA-B27-peptide tolerance. There have been substantial recent advances in both clinical and basic scientific research in this field, including studies of the various animal models of acute anterior uveitis and the HLA-B27 transgenic animals, and these are summarized in this review. To the ophthalmologist, HLA-B27-associated acute anterior uveitis is an important clinical entity that is common, afflicts relatively young patients in their most productive years, and is associated with significant ocular morbidity due to its typically recurrent attacks of inflammation and its potentially vision-threatening ocular complications. Furthermore, to the ophthalmologist and the internist, HLA-B27-associated acute anterior uveitis is also of systemic importance due to its significant association with extraocular inflammatory diseases.

Measurement of HLA class I expression in ankylosing spondylitis

The importance of HLA-B27 in the pathogenesis of ankylosing spondylitis is uncertain: current evidence favours a role for the B27 molecule itself. The possibility that quantitative differences in HLA-B27 expression may exist between patients with ankylosing spondylitis, family members, and control subjects positive for B27 was examined using appropriate monoclonal antibodies, flow cytometry, and a 'model lymphocyte' coated with a known number of mouse immunoglobulin binding sites. No differences were found between the groups. HLA-A2, examined for comparison, was expressed in greater amounts than HLA-B27, but each contributed only 10-20% of the total class I antigens. Homozygotes expressed twice the amount of antigen expressed by heterozygotes. Synovial lymphocytes expressed more class I antigens than peripheral lymphocytes.

The expression of class I major histocompatibility antigens by human retinal pigment epithelium in vitro

Since the expression of class I major histocompatibility antigens by the retinal pigment epithelium (RPE) may be important with regard to ocular immune responses, we investigated this using flow cytometry and compared the RPE cells with the colon carcinoma cell line SW742. Six cultured RPE cell lines were examined. All showed strong basal expression of class I antigen. However, this expression was not maximal, and all the RPE lines tested showed a marked capacity for up-regulation of expression by culture in the presence of interferon-alpha, interferon-gamma, or tumour necrosis factor alpha, cytokines involved in immunological responses.

Acute anterior uveitis and HLA-B27

Acute anterior uveitis is a common ocular disease characterized by inflammation of the iris and ciliary body. In the majority of patients presenting with an acute attack of anterior uveitis, the only clues to the pathogenesis of this disease are its close association with the genetic marker HLA-B27 and the likely triggering role of a variety of gram negative bacteria. HLA-B27 acute anterior uveitis appears to be a distinct clinical entity frequently associated with the seronegative arthropathies, such as ankylosing spondylitis and Reiter's syndrome. Recent advances in our understanding of the structure and function of class I HLA molecules have revealed their fundamental function in antigen presentation and this has led to a reevaluation of their role in disease predisposition.

Differential enhancement of HLA-B27 by interferon

To further examine the role of the HLA-B27 antigen in the pathogenesis of disorders such as anterior uveitis and ankylosing spondylitis, we have measured the level of enhancement of this antigen on peripheral blood lymphocytes and compared it with that of the class I HLA antigens HLA-A2 and HLA-B7 following interferon treatment. We found that the level of enhancement of HLA-B7 was greater than that of HLA-A2 or -B7 following treatment by alpha or gamma interferon (p less than 0.002). Similarly, the level of enhancement of HLA-B7 was greater than that of HLA-A2 (p less than 0.002) (Mann Whitney U-test). A differential enhancement of HLA-B27 by lymphokines may be important in the pathogenesis of HLA-B27-related disorders.