Macrophage polarization and bacterial infections

Macrophages are the first line of defense against pathogens, and the mode of their activation will determine the success or failure of the host response to pathogen aggression. Based on limited numbers of markers, activated macrophages can be classified as classically activated (M1) macrophages that support microbicidal activity or alternatively activated (M2) macrophages that are not competent to eliminate pathogens. The development of high-throughput gene expression methods affords a reappraisal of the concept of macrophage activation in human infectious diseases.

By combining microarray data and conventional approaches, it is becoming clear that the M1 polarization program is associated with gastrointestinal infections (e.g. typhoid fever and Helicobacter pylori gastritis) and active tuberculosis. An M2 signature is observed in lepromatous leprosy, Whipple's disease, and localized infections (keratitis, chronic rhinosinusitis). However, these findings could not be predicted from the analysis of the M1/M2 programs of macrophages stimulated in vitro.

The reappraisal of macrophage polarization by high-throughput methods is critical to understanding the role of macrophage polarization in infectious diseases. Only the identification of individual profiles will support promising therapeutic approaches based on target determination.