Infection can result in two different responses by the host, one focused on elimination and the other focused on 'tolerance' (defined here as coexistence with the infection with few or no sequelae). In PLoS Biology, Begon and colleagues use a longitudinal analysis of field voles caught in the wild to examine immunological parameters, microbial burden and body condition to understand the basis of tolerance of infection. Microparasite burdens increase with age but, unexpectedly, this is associated with better condition of the animal. This improved condition is not correlated with established regulatory factors such as IL-10, TGF-β or Foxp3 but instead is correlated with only GATA-3, a classic T helper type 2 (TH2) transcription factor. GATA-3 is also strongly predictive of host survival but at the cost of diminished fecundity. Not only does this demonstrate the immunological value of studying 'true wild-type' populations, it suggests that type 2 immunity might be understood less as a macroparasite-expulsion mechanism and more as a damage-limitation exercise.

PLoS Biol. (8 July 2014) doi:10.1371/journal.pbio.1001901