Characterization of host responder types after a single Cooperia oncophora infection: kinetics of the systemic immune response.

After primary infection with 100,000 third stage larvae of the intestinal nematode Cooperia oncophora in 3-month-old calves, a high variability in egg output and worm counts is observed. Based on this variability, infected animals can be divided in different responder types. The three major phenotypes can be classified as high, intermediate and low responder animals. We investigated whether calves classified into different responder types show different immune responses during infection. Peripheral blood eosinophil counts and flow cytometric analysis of different lymphocyte subsets of the blood did not reveal major differences between infected and control animals, nor between responder types. However, the levels of Cooperia-specific immunoglobulin (Ig)G1 and IgA during primary infection were significantly higher in intermediate responders than in low responders. In the intermediate responders, isotype specific responses were negatively correlated with parasitological parameters expressing worm expulsion and influence on worm fecundity. Total serum IgE levels were elevated in most of the infected animals. A quantitative positive relationship between worm counts and total serum IgE levels was observed. Based on the observed correlations, we propose a role for the humoral response against the maintenance of the infection in the gut.