Host-Parasite Interaction and Immunological Profiles in Loiasis-Infected Adults in Edo State, South South Nigeria

The immunological mechanisms underlying clinical manifestations of loiasis, including Calabar swellings and subconjunctival migration, remain incompletely characterised in Nigerian populations despite the disease's endemicity in forested southern states. This study investigated host-parasite interaction dynamics and immunological profiles in Loa loa-infected adults in Edo State, South South Nigeria. Peripheral blood samples from 160 adults (80 microfilaraemia-positive and 80 amicrofilaraemic seropositive controls from endemic communities) were collected for immunological profiling. Circulating cytokine levels including IL-4, IL-5, IL-13, IFN-gamma, and IL-10 were measured by multiplex immunoassay. Regulatory T cell and eosinophil counts were determined by flow cytometry and automated haematology analyser respectively. Anti-Loa loa IgG4 and IgE levels were measured by ELISA. Microfilaraemia-positive individuals showed significantly elevated IL-4, IL-13, and IgG4 responses with suppressed IFN-gamma compared to seropositive amicrofilaraemics. Eosinophilia above 1,500 cells per microlitre was present in 74.4 percent of microfilaraemic individuals. Calabar swelling cases showed the highest IL-5 and IgE levels. These immunological patterns suggest a Th2-dominated regulatory response facilitating microfilarial immune escape. The study contributes mechanistic insights relevant to understanding differential clinical outcomes in loiasis and to informing pre-ivermectin screening strategies. Keywords: Loa loa, loiasis, immunological profile, cytokines, Edo State.