Anti-citrullinated peptide antibodies and rheumatoid factor in Sudanese patients with Leishmania donovani infection

Abstract

Objective: The present study evaluated the presence of anti-cyclic citrullinated peptides antibodies (anti-CCP), rheumatoid factor (RF), and circulating immune complexes (CIC) in Sudanese patients infected with the Leishmania donovani parasite.

Patients and methods: Sera were collected from Leishmania infected patients (n = 116) and healthy Sudanese (n = 93). Nineteen Sudanese anti-CCP+ RA patients were included as positive controls. Levels of CIC and anti-CCP were measured by ELISA. Control plate with cyclic control peptides containing arginine instead of citrulline was used to evaluate citrulline specifi c reactivity.

Results: Among Leishmania-infected patients and anti-CCP+ RA patients, most were RF positive (86%), while the frequency of CIC positivity was higher among visceral leishmaniasis (VL) patients (VL 38%; anti-CCP+ RA 24%). When anti-CCP reactivity was analysed, 12% of VL patients were found to be positive. The levels of anti-CCP among VL patients correlated well with the CIC levels found (r = 0.65, P < 0.0001). In RA group, no association was found between CIC and anti-CCP. The possibility that anti-CCP positivity was due to cross reactions with CIC was experimentally ruled out. Contrary to what was seen in Sudanese RA sera, the CCP reactivity was not restricted to citrulline but reacted equally well with the arginine control peptide.

Conclusion: The finding that CCP reactivity was not restricted to citrulline argues that this is more an effect of extensive inflammation and immune activation than a sign of shared pathogenic characteristics with anti-CCP arthritis. Our fi ndings stress the importance to interpret a positive CCP test carefully when evaluated in non-rheumatic conditions or in areas where such infections predominate.