Fixed macrophages are found where microbial invasions are likely to occur, thus, providing a rapid response. The differentiated macrophages possess an enhanced cellular protein synthesis as well as secretory mechanism (Takashiba et al. 1991). Also a tissue macrophage is structurally larger than its precursor (monocyte) and can live for several months. .
Macrophages play a central role in the immune response, since they are important for both innate and adaptive systems. There are clearly four crucial and distinct functions activated macrophages can perform. Firstly, macrophages are involved in the innate defense inflammatory response by phagocytizing pathogens and excreting several cytokines and chemicals that attract other cells to the injured tissue called "chemotactic factors" as well as supporting the repair of tissue. Secondly, macrophages act as "accessory" cells to initiate the lymphocytes of the adaptive immune response; not only by secreting various cytokines, but also by the presentation of antigens to the T cells in order to recognize them and eliminate the pathogen. Thirdly, macrophages function as effectors in the humoral response by possessing cell surface receptors for immunoglobulin substances and are able to phagocytosis antigens that are bound by soluble antibodies. Fourthly, macrophages function in cell mediated immunity, in which the macrophage responds to the cytokines secreted by the activated T cells. The "hyper activated" macrophage gains the ability to become highly antiparasitic and antimicrobial immune cells, specifically against tumor cells. Since macrophages have the ability to perform diverse roles, they exhibit heterogeneous phenotypes in morphology and functions. .
Macrophages perform vital roles during the process of inflammation. Inflammation is the innate first line of defense; it is mainly initiated by resident macrophages.