High levels of parasite-specific IgG4 in the absence of microfilaremia in Loa loa infection.

The specificity of IgG4 as marker of infection has been investigated. The study was based on two well defined clinical groups: amicrofilaremic individuals with verified ocular passage of adult worms of Loa loa, and microfilaremic patients. Both groups were compared to Africans not exposed to loiasis infection and to Europeans. The study revealed that there is no significant difference in the level of parasite-specific IgG4 between individuals with occult infection (i.e. amicrofilaraemic, but infected) and microfilaremic individuals, but there is a significant difference between L. loa infected individuals and Mansonella perstans exposed people. IgG4 of individuals exposed to L. loa infection recognised specific antigens in the molecular weight range 12-30 kDa. We conclude that the elevated level of filarial-specific IgG4 is therefore not dependent upon the presence of circulating microfilariae and that serology using homologous L. loa low molecular weight antigens, can facilitate specific diagnosis of occult loiasis in an endemic area with mixed filarial infections.