With the exception of the alveolar macrophages, which are uniquely dependent on aerobic metabolism for energy production, monocytes and macrophages are facultative anaerobes. Like phagocytosis in neutrophils, phagocytosis in monocytes and macrophages is associated with an oxidative burst and stimulation of the hexose monophosphate shunt. Adhesion, chemotaxis, and activation of phagocytosis are also similar in the two types of cells, although the macrophage is better than the neutrophil at phagocytosis and performs chemotaxis less rapidly and efficiently. The macrophage is also capable of oxygen-independent bactericidal activity that may depend on lytic activity. Furthermore, stimulated macrophages are capable of producing nitric oxide.
Macrophages can also present processed antigen to B cells to elicit a humoral response.
The cytotoxicity involves oxidative metabolism, the production of nitric oxide and cytokines, and the secretion of cytotoxic mediators. They also are required for angiogenesis and wound healing and are able to induce neovascularization and endothelial cell proliferation. These disorders predominantly affect infants and young children but have also been described in young adults. Because the LCH syndromes represent a continuum of disease that frequently cannot be broken down into these rigid and arbitrary designations, other classification systems that relate to age at diagnosis, extent of disease, and presence of organ dysfunction have been developed. The signs and symptoms of the LCH syndromes depend on the organs involved.