Abstract
The adaptive immune system is critical to an effective response to infection in vertebrates, with T-helper (Th) cells pivotal in orchestrating these responses. In natural populations where co-infections are the norm, different Th responses are likely to play an important role in maintaining host health and fitness, a relationship which remains poorly understood in wild animals. In this study, we characterised variation in functionally distinct Th responses in a wild population of Soay sheep by enumerating cells expressing Th-subset specific transcription factors and quantifying Th-associated cytokines. We tested the prediction that raised Th1 and Th2 responses should predict reduced apicomplexan and helminth parasite burdens, respectively. All measures of Th-associated cytokine production increased with age, while Th17- and regulatory Th-associated cytokine production increased more rapidly with age in males than females. Independent of age, sex, and each other, IL-4 and Gata3 negatively predicted gastro-intestinal nematode faecal egg count, while IFN-γ negatively predicted coccidian faecal oocyst count. Our results provide important support from outside the laboratory that Th1 and Th2 responses predict resistance to different kinds of parasites, and illustrate how harnessing specific reagents and tools from laboratory immunology will illuminate our understanding of host-parasite interactions in the wild.
Highlights
The adaptive immune system is critical to an effective response to infection in vertebrates, with T-helper (Th) cells pivotal in orchestrating these responses
Previous studies in wild Soay sheep found that strongyle faecal egg counts (FEC) was positively associated with coccidian FOC8, we found no evidence for significant associations in our smaller data set
Our results provide important evidence that measuring immune phenotypes associated with different functional arms of the Th response can help us to predict the parasite burden of wild mammals
Summary
The adaptive immune system is critical to an effective response to infection in vertebrates, with T-helper (Th) cells pivotal in orchestrating these responses. A shortcoming of many field studies of immunity to date has been the inability to quantify variation in these functionally different cell types, often relying instead on generic measures of immunity, such as skin swelling or natural antibody responses to novel antigen challenge[4,5]. This has largely been due to the lack of suitable immunological tools in non-model systems which would enable the abundance and functionality of immune cells to be quantified. A broad understanding of adaptive immune function can obtained by quantifying the master transcription factors expressed by Th cells and the cytokines released upon activation (Fig. 1)
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