Anti-citrullinated peptide antibodies in Sudanese patients with Leishmania donovani infection exhibit reactivity not dependent on citrullination.

Abstract

African patients with Leishmania donovani infections have signs of strong systemic inflammation and high levels of circulating immune complexes (IC) and rheumatoid factor (RF), all serologic markers of rheumatic disease. As inflammation in general is associated with citrullination, we sought to investigate ACPA responses in Sudanese Leishmania patients. Serum samples were collected from Sudanese patients with visceral leishmaniasis (VL) and post-kala-azar dermal leishmaniasis (PKDL) as well as from ACPA-positive Sudanese rheumatoid arthritis patients and compared to healthy Sudanese controls. Levels of circulating C1q-binding IC and anticyclic citrullinated peptide 2(CCP2) were investigated using ELISA, and RF was measured with nephelometry. C1q adsorption was carried out to investigate anti-CCP2 content in IC. Citrulline specificity was evaluated with control plates with cyclic arginine-containing control peptides. Leishmania-infected patients had elevated levels of RF and circulating IC but also a significant increase in anti-CCP2 (12%) as compared to healthy controls. Anti-CCP2-positive Leishmania patients displayed lower anti-CCP2 levels than Sudanese patients with rheumatoid arthritis (RA), and anti-CCP2 levels in Leishmania patients showed a continuum not resembling the dichotomous pattern seen in patients with RA. Whereas the anti-CCP reactivity of Sudanese RA sera was strictly citrulline dependent, anti-CCP2-positive Leishmania sera reacted equally well with ELISA plates containing arginine control peptides. There was a strong correlation between anti-CCP2 and circulating IC among the Leishmania patients, but IC depletion only marginally diminished anti-CCP2 levels. Our findings stress the importance to interpret a positive CCP test carefully when evaluated in non-rheumatic conditions associated with macrophage activation.