Human macrophages expressing an undefined antigen detected by the 27E10 monoclonal antibody are observed in acute inflammatory exudates in cases of contact dermatitis, gingivitis, and psoriasis, but are absent in chronic inflammation arising from osteoarthritis, tuberculoid leprosy, and rheumatoid arthritis. Accumulation of 25F9-positive macrophages correlates with tumour progression and poor prognosis. These studies suggest that phenotypic analysis of macrophage subsets might be of use diagnostically, even if the specific role of these macrophage populations is unclear. The term activated macrophages is reserved for macrophages possesing specifically increased functional activity. The process of differentiation is not to be confused with activation , the process trough which differentiated macrophages acquire an increase ability to perform specific functions.
Resident macrophages are, however, phagocytic and chemotaxic and retain some proliferative capacity.
There are two stages of macrophage activation, the first being a primed stage in which macrophages exhibit enhanced MHC class II expression, antigen presentation, and oxygen consumption, but reduced proliferative capacity. The agent that primes macrophages for activation is IFN- , a product of stimulated and cells. The distinction between primed and fully activated macrophages is usually arbitrary, depending in large part on the stimulus used and the functional assessed. Macrophages stimulated for tumouricidal activity show decreased MHC class II gene transcription and are generally poor presenters of antigen, despite their secretion of IL-1. Moreover, the process of tumour cell lysis is a multistep event, determined by the sensitivity of the target cell itself.