A longitudinal study of local and peripheral isotype/subclass antibodies in Dictyocaulus viviparus-infected calves.

Although infection with the bovine lungworm, Dictyocaulus viviparus, stimulates high levels of resistance, the mechanisms involved in immunity to this parasite remain poorly understood. In an attempt to address the possible role of antibody in protective immunity, a longitudinal study was carried out in which the levels of both local and peripheral parasite-specific IgG, IgG1, IgG2, IgM and IgA were measured by ELISA. Five calves were infected orally with ten third stage larvae per kilogram on days 0, 65 and 112. Three challenge controls remained uninfected until day 112. Peripheral responses were measured in serum collected weekly and local responses were measured in bronchoalveolar lavage fluid (BALF) collected pre-infection and on two occasions after each infection. After the secondary infection, there were increases in respiratory rates in all the calves, but four of five calves had no first stage larvae (L1) in their faeces, suggesting that the parasites reached the lungs but did not develop to patency. Respiratory rates remained within normal limits after the tertiary infection and there were no parasites in the lungs at postmortem. Locally, in BALF, levels of all the antibody isotypes/subclasses increased after the primary infection, then again after the secondary infection. The highest levels of antibody were detected after the tertiary infection, when the calves were fully immune. In contrast, serum antibody levels increased from day 21 after primary infection and rose again after secondary infection, but thereafter slowly declined, with no increases after tertiary infection. Our findings suggest that the local antibody response was important in the immune response to D. viviparus infections in calves.