On the hunt for helminths: innate immune cells in the recognition and response to helminth parasites

The generation of protective immunity to helminth parasites is critically dependent upon the development of a CD4(+) T helper type 2 cytokine response. However, the host-parasite interactions responsible for initiating this response are poorly understood. This review will discuss recent advances in our understanding of how helminth-derived products are recognized by innate immune cells. Specifically, interactions between helminth excretory/secretory products and host Toll-like receptors and lectins will be discussed as well as the putative functions of helminth proteases and chitin in activating and recruiting innate immune cells. In addition, the functional significance of pattern recognition by epithelial cells, granulocytes, dendritic cells and macrophages including expression of alarmins, thymic stromal lymphopoetin, interleukin (IL)-25, IL-33 and Notch ligands in the development of adaptive anti-parasite Th2 cytokine responses will be examined.