Composition and Function of Haemolymphatic Tissues in the European Common Shrew

Bray, Daniel P.; Bennett, Malcolm; Stockley, Paula; Hurst, Jane L.; Kipar, Anja

We hypothesised that common shrews, which are not expected to survive beyond the first breeding season, would gain little benefit from investing their limited resources in immunity and immune system maintenance, at the expense of reproduction. Instead, we predicted that wild shrews would demonstrate only limited responses to parasites, and that their immune system would show signs of deterioration with age. The aim of the study was therefore to evaluate the capacity of sub-adult and adult shrews to mount immunological responses. We examined and compared the structure, composition and function of relevant haemolymphatic tissues including the pancreas of Aselli, in wild-caught common shrews of different ages pre and post maturation, and the extent and type of inflammatory reactions produced in response to naturally occurring parasitic infections. Light and electron microscopy were applied in conjunction with immunohistological characterisation of leukocyte populations. Contrary to our predictions, our results indicated that shrews are capable of mounting immune/inflammatory responses throughout their entire life span. While some degree of lymphatic exhaustion was obvious in adult animals (perhaps as a result of age-related changes, or reduced investment in immunity as a consequence of breeding effort), there was also evidence of some degree of compensation, in the form of storage of plasma cells particularly in the pancreas of Aselli, possibly as a defence against previously encountered parasites.