Clinical, serologic, and immunogenetic features of familial idiopathic inflammatory myopathy.

OBJECTIVE: To describe the clinical, serologic, and immunogenetic features of familial idiopathic inflammatory myopathy (IIM) and to compare these with the features of sporadic IIM. METHODS: Clinical signs and symptoms, autoantibodies, HLA-DRB1 and DQA1 alleles, and GM/KM phenotypes were compared among 36 affected and 28 unaffected members of 16 unrelated families in which 2 or more blood relatives developed an IIM. In addition, findings in patients with familial IIM were compared with those in 181 patients with sporadic IIM. The families included 3 pairs of monozygotic twins with juvenile dermatomyositis, 11 families with other siblings or relatives with polymyositis or dermatomyositis, and 2 families with inclusion body myositis. RESULTS: The clinical features of familial IIM were similar to those of sporadic IIM, although the frequency of myositis-specific autoantibodies was lower in familial than in sporadic IIM. DRB1*0301 was a common genetic risk factor for familial and sporadic IIM, but contributed less to the genetic risk of familial IIM (etiologic fraction 0.35 versus 0.51 in sporadic IIM). Homozygosity at the HLA-DQA1 locus was found to be a genetic risk factor unique to familial IIM (57% versus 24% of controls; odds ratio 4.2, corrected P = 0.002). CONCLUSION: These findings emphasize that 1) familial muscle weakness is not always due to inherited metabolic defects or dystrophies, but may be the result of the development of IIM in several members of the same family, and 2) multiple genetic factors are likely important in the etiology and disease expression of familial IIM, as is also the case for sporadic myositis, but DQA1 homozygosity is a distinct risk factor for familial IIM.

Dual effect of ciliary body cells on T lymphocyte proliferation.

The interaction between organ-resident cells from the anterior uvea of the eye and T helper (Th) cells was investigated. Cells from Lewis rat ciliary body processes (CB cells), grown in tissue culture using an explant technique, could be induced to express major histocompatibility complex class II (Ia) antigens by incubation with rat interferon-gamma. Ia+ CB cells only poorly functioned as antigen-presenting cells (APC) for a syngeneic, uveitogenic Th cell line specific for the retinal soluble antigen (SAg). Moreover, if added to an Ag-driven lymphocyte proliferation assay in the presence of conventional APC, the rat CB cells had an inhibiting effect on Th proliferation. This inhibitory activity was not species specific, since similar effects were observed with bovine and human ciliary epithelial cells. The suppressive activity of CB cells was composed of a soluble factor, as well as a membrane-associated inhibitor. The soluble activity did not appear to be related to transforming growth factor-beta (TGF-beta), since no reversal of inhibition by a neutralizing antibody to TGF-beta was found. Part of the soluble inhibitory activity could be reversed by indomethacin treatment. The membrane-associated component was trypsin sensitive, suggesting a protein molecule. After abrogation of the inhibitory capacity by trypsin treatment and fixation by glutaraldehyde, CB cells effectively presented SAg to Th cells. These data suggest that CB cells are capable of mediating both Ag presentation and inhibition of Th cell proliferation.

Endotoxin-induced production of inflammatory mediators by cultured ciliary epithelial cells.

Systemic injection of bacterial endotoxin (Lipopolysaccharide, LPS) in experimental animals induces anterior uveitis without major pathological changes in other organs. The present study investigates the effect of LPS on production of inflammatory mediators in cultured bovine pigmented ciliary epithelial cells (CB-cells) by means of radioimmunoassays and bioassays. LPS was found to stimulate CB-cells to secrete prostaglandin E2 and prostacyclin (assayed as its stable metabolite 6-keto-prostaglandin F1a), but not leukotriene B4 or thromboxane A2 (assayed as its stable metabolite thromboxane B2). CB-cells produced membrane-associated interleukin 1-activity in response to LPS, but no tumor necrosis factor-activity was found after challenge of CB-cells with LPS. The direct effect of LPS on production of inflammatory mediators by cells from the anterior uvea could play a role in the pathophysiology of endotoxin-induced uveitis.

Induction of MHC class II antigen in cultured bovine ciliary epithelial cells.

The expression of major histocompatibility complex (MHC) class II antigens in cultured bovine ciliary epithelial cells was investigated by means of indirect immunohistochemistry and immunocytofluorometry. Ciliary epithelial cells grown in control tissue-culture medium did not express MHC class II. However, after incubation with bovine gamma-interferon (IFN-G) in concentrations as low as 0.3 units/ml, nearly all cells stained for MHC class II. Tumor necrosis factor increased IFN-G-induced MHC class II expression. A reduction in IFN-G-induced MHC class II expression was observed with dexamethasone, prostaglandin E2 and alpha-interferon. To test whether MHC class II expression in response to IFN-G was specific for the ciliary epithelium, several intraocular tissues were grown in culture and incubated with IFN-G. MHC class II expression was observed in all tissues tested for response to IFN-G, but at different sensitivities. Retinal pigment epithelium and ciliary epithelium exhibited the highest sensitivity, followed by corneal endothelium and lens epithelium; the lowest sensitivity was observed for retinal vascular pericytes. The results are discussed in the context of MHC class II expression on the ciliary epithelium in anterior uveitis.