Larval ascariasis elicits a prominent IgA and IgG1/2 antibody response to adult Ascaris excretory/secretory antigens in pigs

Roundworm infections result in morbidity, causing significant health and economic concerns in humans and pigs, respectively. We investigated the humoral responses of <i>Ascaris suum</i> infected pigs before and after transition from larval to adult stage and confirmed our previous report on the diagnostic value of human <i>Ascaris</i>-specific antibodies. We evaluated the systemic and mucosal humoral responses in <i>Ascaris</i> infected pigs at 14- and 35-days post-infection (dpi). <i>Ascaris</i>-specific antibodies against larval and adult worm antigens and adult excretory/secretory (ES) products in serum, broncho-alveolar lavage fluid and intestinal mucus were quantified by ELISA. IgA⁺ B cells in jejunal/ileal mesenteric lymph nodes (mLNs) were investigated using flow cytometry. ES products reliably reported parasite-specific IgM, IgA, IgG and IgG1/2 present in sera at 35 dpi (adult stage) and even at 14 dpi (larval stage). Neither variable worm burdens nor the coinfection with <i>Salmonella</i> affected the ES-specific antibody profiles. Extracts of the third-stage larvae (L3) were less suited but clearly reported L3-specific secretory IgA in lung and intestine. IgA⁺ B cells expanded in lymph nodes draining jejunum and ileum at day 14 post infection but leveled down to background controls at 35 days after primary infection. A strong correlation between sIgA and eosinophil numbers was seen in the lung, validating previous observations in mice for the definite host. The balanced targeting of L3-somatic antigens and adult ES by sIgA in mucosal sites contrasted with prominent parasite-specific IgA in sera which exclusively reacted to ES products. Collectively, our data indicate extensive antigenic overlap between <i>Ascaris</i> life stages, facilitating the detection of pre-patent and larval stage infection. We further point out distinct mucosal/systemic IgA responses in <i>Ascaris</i> infection which deserve further functional investigations.