Exploring the full spectrum of macrophage activation

Abstract

Macrophages exhibit remarkable plasticity, which allows them to change their physiology in response to various different environmental stimuli. The physiological characterization of each of these different macrophage populations may help to explain disease aetiologies. The identification of biochemical markers that are specific for each of these macrophage populations may allow us to delete specific populations of macrophages, or to diagnose disease progression or resolution by the presence or absence of these populations. Three populations of activated macrophages have been identified with unique characteristics. In addition, examples from disease states are given, in which macrophages share characteristics of more than one population. This provides a conceptual framework for a large number of different macrophage subpopulations based on this simple three-cell scaffold. Some pathogens can exploit these changes in macrophage physiology and use macrophages for intracellular growth. During disease progression, it is probable that macrophage populations will shift their phenotype, and this shift can contribute to disease resolution or progression.