Rickettsial disease IFA-IgG titres in Auto-Immune diseases; what do they imply?

Abstract

INTRODUCTION: Rickettsial infections are known to present mimicking autoimmune disorders. The gold standard diagnostic test for rickettsial diseases is based on the detection of IgM and or IgG antibodies against these infections by immuno-fluorescent technique (IFA). During the IFA test, patient sera containing anti rickettsial antibodies are made to react with rickettsial antigens that are grown in cell culture media. However, presence of nuclear material in these cell cultures may react with anti-nuclear antibodies that are produced in autoimmune disorders and cause a false positive immunofluorescent signal. OBJECTIVES: To evaluate the reactivity of rickettsial disease among patients with auto immunity diseases. METHOD: In order to evaluate the reactivity of rickettsial disease IFA-IgG test [IFA-IgG-OT (Orientia tsutsugamushi) and IFA-IgG-SFG (spotted fever group)] among patients with autoimmune diseases, an analytical cross-sectional study was carried out using sera of 38 patients with confirmed auto-immune diseases. RESULTS: The 38 patients included 15 systemic lupus erythematosus (SLE), 5 autoimmune-thyroiditis, 13 idiopathic-thrombocytopenia (ITP), 4 autoimmune-haemolytic-anaemia (AIHA), 1 polymyositis, 1 polyglandular syndrome and 1 Anti-phospholipid syndrome. The IFA-IgG reactivity of ≥ 1:128 was noted in 14/38 (37%); IFA-IgG-SFG in 7, IFA-IgG-OT in 3 and for both in 4. Of the 14 patients who had shown reactivity to IFA-IgG 2 had a titre of 1:128, four had a titre of 1:256, five had a titre of 1:512, three had >1: 1024 . 57% among the 14 who had shown reactivity were diagnosed as SLE, 21.4 % had ITP, 14.3% had AIHA, and 7.1% had polymyositis. None were diagnosed with thyroiditis. CONCLUSIONS: There was a significant reactivity of Rickettsial disease IFA-IgG assay in auto-immune diseases. Further studies are needed in order to ascertain whether this is due to recent rickettsial infections, false positive cross reactivity of autoimmune antibodies with rickettsial antigens or with cell culture nuclear antigens.