Macrophages activated by the Th2 cytokines IL-4 and IL-13 are found in high numbers at the site of helminth infection.  Macrophage accumulation in this setting can result either from local expansion of the resident population or recruitment of blood monocytes. Proliferative expansion of macrophages in response to IL-4 receptor signalling occurs in a broad range of tissues in both helminth infection and non-infectious settings such as tissue injury.  Depending on the infectious agent, host genotype or site of infection/injury, the increase in macrophage number may be due predominantly to proliferation of resident cells or recruitment of monocytes from the blood. Critically, the capacity of macrophages to respond to IL-4 or IL-13 at the site of infection or injury is dictated by local tissue-specific signals. These signals are needed to amplify the type 2 immune response to a level sufficient for parasite control or tissue repair, but may also result in excessive or inappropriate collagen deposition, i.e fibrosis.