Immune-like Phagocyte Activity in the Social Amoeba

摘要

Social amoebae feed on bacteria in the soil, but they aggregate when starved and form a migrating slug that will undergo fruiting body morphogenesis to produce terminally differentiated spores and stalk cells. We describe a new cell type in the social amoeba which appears to provide detoxification and immune-like functions, which we term Sentinel (S) cells. S cells were observed to engulf bacteria and sequester toxins while circulating within the slug, eventually being sloughed off. A Toll/Interleukin-1 Receptor (TIR) domain protein, TirA, was also required for some S cell functions and for vegetative amoebae to feed on live bacteria. This apparent innate immune function in social amoebae, and the use of TirA for bacterial feeding, suggests an ancient cellular foraging mechanism that may have been adapted to defense functions well before the diversification of the animals.