The relationship between responsiveness against gastrointestinal nematodes in lambs and the numbers of circulating IgE-bearing cells

The objective of this study was to determine if any relationship exists between responsiveness against gastrointestinal nematodes (GI) in lambs and circulating IgE-bearing cells. Scottish Blackface lambs that were grazing on pasture infected with Teladorsagia circumcincta (T. circumcincta) were ranked in order of their cumulative resistance to nematode infection as determined by their faecal egg counts (FECs) from material taken throughout the grazing season. The 10 lambs that had the lowest egg count rankings termed “responders” and the 10 lambs that had the highest egg count rankings termed “non-responders”, were selected using data from the whole season or the middle or end of the grazing season. The number of circulating IgE-bearing cells present in the selected responder and non-responder lambs was investigated. The study was followed for two grazing seasons. Results showed that there were higher numbers of circulating IgE-bearing cells in the blood of responder lambs when compared to non-responders in the lambs selected from the middle of the season during both grazing seasons. A significant difference in the number of these IgE-bearing cells in responder and non-responder lambs was also demonstrated at the last two time points (p < 0.05) of the initial grazing season. FACS analysis confirmed that IgE-bearing cells were found predominantly among lymphocytes/monocytes. The present study provides further evidence for an active role for IgE antibody in nematode immunity, and suggests that these circulating IgE-bearing cells might serve as additional markers for selecting animals that are responsive against T. circumcincta infections in lambs.