Alternatively activated macrophages in helminth infections

Helminthic parasites can trigger highly polarized immune responses typically associated with increased numbers of CD4(+) Th2 cells, eosinophils, mast cells, and basophils. These cell populations are thought to coordinate an effective response ultimately leading to parasite expulsion, but they also play a role in the regulation of associated pathologic inflammation. Recent studies suggest that macrophages, conventionally associated with IFN-gamma-dominant Th1-type responses to many bacteria and viruses, also play an essential role in the Th2-type inflammatory response. These macrophages are referred to as alternatively activated macrophages (AAM phi s) as they express a characteristic pattern of cell surface and secreted molecules distinct from that of classically activated macrophages (CAM phi s) associated with microbe infections. In this review, we will discuss recent findings regarding the role of AAM phi s in the development of disease and host protection following helminth infection.