HUMAN ONCHOCERCIASIS IN NIGERIA - ISOTYPIC RESPONSES AND ANTIGEN RECOGNITION IN INDIVIDUALS WITH DEFINED CUTANEOUS PATHOLOGY

Antigen (AE)-specific isotype responses to Onchocerca volvulus Ag (OvA g) were assessed by enzyme-linked immunosorbent assay and immunoblot i n 123 residents of a mesoendemic area in northern Nigeria and 16 Niger ians from a nonendemic area. Individuals from an endemic area were div ided into Six groups on the basis of cutaneous onchocercal pathology: acute papular onchodermatitis (APOD), chronic papular onchodermatitis (CPOD), lichenified onchodermatitis (LOD), atrophy (ATR), depigmentati on (DPM) and normal skin, high microfilarial load (NSHMF). Immunoglobu lin (Ig) G1-4 levels were all significantly associated with residence in an endemic area after controlling for age and sex (all P values = 0 .0001). Both IgG1 and IgG3 were significantly associated with onchocer cal clinical category after controlling for age, sex, and microfilaria l load (P = 0.0031 and 0.0035, respectively). The IgG1 and IgG3 respon ses were both highest in LOD and lowest in NSHMF and ATR, respectively . A significant inverse association was found between IgG1 levels and microfilarial load after controlling forage, sex, and clinical categor y (P = 0.0061), On immunoblotting, 20 (44.4%) of 45 individual onchoce rciasis sera contained IgG4 antibodies against a band of 29-31 kD, whi ch was not recognized by pooled sera from individuals with other filar ial infections. There was heterogeneity of antigen recognition within each of the onchocercal clinical groups, which together with the small numbers examined by immunoblotting, limits interpretation Nevertheles s, some differences in patterns of antigen recognition were found betw een the onchocercal groups. The LOD group demonstrated prominent immun oreactivity in IgG1 and IgG3 while a general paucity of low molecular weight reactivity was seen with NSHMF in IgG1-3 subclasses, but there was no specific banding pattern that differentiated NSHMF from those w ith pathology. Comparison of microfilariae-positive (mf+) and mf- indi viduals with onchocercal skin disease revealed significantly higher le vels of all IgG subclasses and higher overall scores on semiquantitati ve assessment of immunoblots for IgG1. IgG2, and IgG4 for mf+ individu als. Differing isotypic responses may play a role in the pathogenesis of the clinical spectrum of cutaneous onchocerciasis.