In addition, GM-CSF appears in the serum. The production of functionally distinct macrophage populations gives the nonspecific immune system added flexibility to respond to immunological or inflammatory stimuli. In addition, the orchestration and regulation of cytokine production during inflammatory responses constitute a key determinant of both the resolution of challenge and the limitation of host tissue damage. Hence, the sequential appearance within inflammatory lesions may allow the most appropriate response at a given stage of an immune response. Analysis of temporal production of cytokines during immune responses suggests that different macrophage populations participate at various stages, or that the changing conditions within the lesion differentially affect the functions of distinct macrophage populations.
Several studies correlate the presence of certain macrophage populations with disease states.
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.