Associations between clinical disease, circulating antibodies and C1q‐binding immune complexes in human onchocerciasis

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Abstract
Summary Onchocerciasis is a disease where often there are high levels of serum antibodies and high parasitic loads. The role of immune complexes in the development of the disease is investigated here by studying non‐specific and Onchocerca volvulus specific immune complex levels, as well as the antibody concentrations, in the sera of 372 people living in either Southern (199) or Northern (173) Sudan; sera from Sudanese individuals (31) and Caucasians (21) living outside the onchocerciasis endemic area were also tested. The levels of non‐specific immune complexes (NS‐IC) in these sera were measured by a solid phase radio‐immunoassay and those of O. volvulus‐specific immune complexes (OV‐IC) by an assay measuring antibody‐excess complexes using Clq‐coated plates. The concentrations of O. volvulus IgG antibodies were measured by ELISA. Immune complex and antibody levels of the serum donors were compared with regard to their clinical status due to onchocerciasis. These clinical changes were classified according to onchocercal lesions related to either (a) the active destruction of microfilariae (acute changes), or (b) the long term tissue alterations (chronic changes). Data was analysed using the Odds Ratio method. A negative association between microfilarial load and immune complex level was found, with the higher levels of OV‐IC present in patients with the lower levels of dermal microfilariae (i.e., less than 10 mf/mg). Significant associations between immune complex levels and the severity of onchocercal disease were also found. Levels of OV‐IC specific immune complexes were higher in infected individuals carrying dermal onchocercal lesions than in those without such clinical changes; there was no apparent relationship between these levels and the