ROLE OF HUMAN T LYMPHOTROPIC VIRUS TYPE I ON PATHOGENESIS OF SJOGREN'S SYNDROME

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Human T-cell lymphotropic virus type I (HTLV-I) is a human retrovirus, originally identified as an aetiological agent of adult T cell leukemia, and closely associated with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). We previously demonstrated that the HTLV-I seroprevalence in Sjogren's syndrome (SS) patients was 23.0%, which was significantly higher than those of the normal blood donors (3.4%). The age-adjusted summary odds ratio of HTLV-I infection in SS patients as compared with normal blood donors, estimated by the Mantel-Haenszel procedure, was 3.1. Furthermore, etiologic fraction, the proportion of SS patients attributable to HTLV-I infection, was estimated to be 17.6%.At first, we investigated whether SS was complicated with HAM patients. The clinical feature and histological findings of SS and the prevalence of serum autoantibodies were examined 14 patients with HAM.All patients with HAM histologically showed a mononuclear cell infiltration in the labial … More salivary glands. According to the preliminary criteria for SS proposed by the European Community, definitive SS was diagnosed in 8 patients and probable SS in 4 patients. There was no significant difference in the prevalence of autoantibodies including rheumatoid factor, anti-nuclear, anti-SS-A (Ro) and anti-SS-B (La) antibodies among 8 HAM patients with definitive SS,HTLV-I-seropositive and- seronegative SS patients. The CD4^+ T cells preferentially infiltrated into the salivary glands in HAM patients as well as the salivary glands of patients with HTLV-I-seropositive and -seronegative patients.Next, apoptosis in labial salivary glands from HTLV-I-seropositive and -seronegative SS patients was studied. Apoptotic cell death was detected in epithelial cells (acinus and ducts) of labial salivary glands. Fas antigen was found on epithelial cells in labial salivary glands. Fas ligand was stained in the infiltrated lymphocytes. There was no significant difference in above findings between HTLV-I-seropositive and -seronegative SS patients.We examined the presence of HTLV-I provirus DNA of both peripheral blood lymphocytes and labial salivary glands form 7 HTLV-I seropositive patients with SS by nested two-step PCR.All 4 independent regions of the HTLV-I genomic, including LTR,gag, pol and pX,were readily amplified from DNA of peripheral blood lymphocytes and tissues of all the seropositive patients. Next, we studied the copy number of HTLV-I in each sample DNA by semiquantitative PCR.The ratio of the copy number between tissue and lymphocytes was variable, but 3 out of 4 SS patients without HAM gene very high values. These findings suggest that HTLV-I infected cells may accumulate in the salivary gland of these patients. From the above findings, it seems likely that peripheral blood T cells from HAM patients preferentially infiltrate into the salivary glands, and then the infiltrated T cells induce SS the pathological changes in the exocrine organs. We studied, therefore, transmigratory activity of circulating T cells from HAM patients through reconstituted basement membrane. Transmigratory activity of lymphocytes was assayd in Transwell cell-culture chambers. We applied the circulating CD4^+ cells from patients with HAM and normal subjects on Transwell cell-culture chambers, and then counted the number of transmigrated cells. The percentage of transmigrated CD4^+ cells from HAM patients was significantly higher than that from normal subjects. Furthermore, HTLV-I proviral DNA quantified in the transmigrated CD4^+ cells from HAM patients were 2 to 8 fold more frequent than that in the non-transmigrated CD4^+ cells. These findings indicate that HTLV-I infected CD4^+ cells of HAM patients have up-regulated transmigratory activity through reconstituted basement membrane.In summary, our findings strongly support the idea that HTLV-I is involved in the pathogenesis of the disease in a subset of patients with SS in endemic areas. Less