Eosinophils and Eosinophilia in parasitic infections

Eosinophilia represents a hallmark of many parasitic infections, particularly those caused by helminthes. Although eosinophils have been shown to be potent in killing parasites, especially at the larval stage in vitro; their precise function in parasitic infection in vivo remains poorly understood. It has long been held that the primary function of the eosinophil is protection against helminth parasites but few data are available to prove this unequivocally. Moreover, eosinophils are responsible for a considerable amount of the inflammatory pathology accompanying helminth infections. Recent data from the literature suggests other functions for this cell population, such as acting as antigen presenting cells or as regulatory cells with a down-regulating effect of the Th1 immune response. This chapter will provide an overview of our current knowledge concerning eosinophil role and function in parasitic infections.