Senescence in immunity against helminth parasites predicts adult mortality in a wild mammal

Abstract

The decline of resistance in old age Infection, immunity, and demography are rarely measured simultaneously, despite being intertwined. Froy et al. measured an immune marker of resistance to infection by worm parasites (helminths) in Soay sheep off the remote Atlantic island of St. Kilda (see the Perspective by Gaillard and Lemaître). They used a library of 2000 blood samples from 800 known individuals that have been left to run wild and unmanaged. Resistance declines as the sheep age, which reduces a sheep's chances of surviving the winter. Helminths are an important component of many natural systems, including humans, and may thus become an increasing burden on health with age. Science , this issue p. 1296 ; see also p. 1244