Larval Exposure Rather than Adult Worm Burden Shapes Systemic and Mucosal Th2 Immunity in Ascaris suum Infected Pigs

Ascariasis is a prevalent parasitic infection in both humans and pigs, resulting in significant human morbidity and economic losses in the porcine industry. Experimental infections are often studied by mimicking natural settings, exposing the host to frequent, small doses (trickle infection) or by administering a single (bolus) dose of infective eggs. However, the impact of infection schemes and doses on the host immune response inA. suum infected pigs is still unclear. Using trickle and bolus infections and applying different doses, we found systemic GATA3+CD4+ T cells and eosinophils increased dose-dependently during A. suum body migration, while CD4+ T cells that specifically recognize A. suum antigens showed no association with the infection dose. In contrast, all dose-dependent differences were resolved by 8-9 weeks post infection, when adult worms were present. The results further showed that adult worm burden did not differ detectably across all groups, though a high intragroup variability was observed. Local type 2, germinal center B cell, and Tfh cell responses were dose-dependent in bolus infected animals only. Our data suggest that the initial immune response generated during A. suum larval migration is pivotal in determining the fate of the antiparasite response and adult worm population. Moreover, our results indicate that the host can regulate the worm load independent of the infection dose and scheme.