Onchocerca volvulus
infection usually results in a predominantly immunopermissive reaction called generalized
onchocerciasis and characterized by high microfilarial burden and immunological tolerance to the worms. Rarely, however,
infection leads to the sowda form of the disease displaying low microfilarial numbers, i.e. microfilarial control, and a T helper 2 (Th2)-type immune response including high
immunoglobulin (Ig)E levels, and
interleukin (IL)-13 being one of the key
cytokines. The aim of this study was to investigate a possible association of a variant of the
IL-13 gene, which confers an
IgE-independent risk for
asthma and atopy, with the immunologically hyper-reactive sowda form of
onchocerciasis. Genotyping for the
IL-13 variant Arg110Gln revealed a highly significant association of Arg110Gln with the sowda form (relative risk of 2.98, n = 19 patients), whereas the frequency of the variant was significantly lower in patients with generalized
onchocerciasis (n = 92 individuals). Sowda patients had higher
IgE levels than those with generalized
onchocerciasis. Logistic regression analysis revealed that
IgE and
IL-13 are independent variables, each increasing the relative risk for sowda. Arg110Gln has been suggested to lead to enhanced
IL-13 signaling and thus may be involved in shifting the immune reaction towards the hyper-reactivity characteristic for the sowda form, thereby promoting defense mechanisms.