Host response to simultaneous infections with Eimeria acervulina, maxima and tenella: a cumulation of single responses.

It is well known that broilers may be infected by different Eimeria strains at the same time and that different species infect specific parts of the gut. Cell mediated responses play a major role in the immune response in broilers after infection with Eimeria species. The cell mediated responses could be intestinal site specific and if this site specific cell mediated responses differ when other parts of the intestine are infected is unknown. To investigate this in the Eimeria infection model we analyzed the cell mediated responses to an infection with a single Eimeria species and with a mixture of different species of Eimeria such as E. acervulina, E. maxima or E. tenella in the duodenum, jejunum and caecum. The immune parameters we measured were intestinal T-cell and macrophage population dynamics as well as local cytokine mRNA expression. These parameters were related to the amount of Eimeria DNA that was measured in the intestine with an Eimeria strain specific quantitative PCR. The results showed that the strongest immune response was induced in the specific part of the intestine that was affected by each Eimeria strain. An E. acervulina infection mainly induced a duodenal CD8(+) T-cell and macrophage response as well as an increased IL-2, IL-4, IL-8, IL-10, and INF-gamma response. An E. maxima infection mainly induced a CD4(+) T-cell and macrophage response but also an increased IL-4, IL-8, and very strong INF-gamma (300-fold) expression in duodenum and jejunum. E. tenella induced a CD4(+) T-cell, macrophage response and an increase in the IL-2, IL-4, IL-8, IL-10, IL-18 and INF-gamma response in the caecum. The infection with a mixture of Eimeria species resulted in responses per intestinal segment that were similar to that observed following the single species infection. No synergistic or competitive effects were thus observed following a primary infection with a mixture of Eimeria species. In contrast, we observed an accumulation of the local effects of the single infections.