Differential actions of pituitary adenylyl cyclase-activating polypeptide and interferon gamma on Th2- and Th1-associated chemokine expression in cultured murine microglia.

Microglia are the immune cells that reside in the central nervous system (CNS). Following the facial nerve injury in the mouse, microglia are activated in the facial motor nucleus, coincident with an increase in the proinflammatory cytokine interferon-gamma (IFN-γ). The authors have previously shown that maximal facial motoneuron (FMN) survival after injury depends on the CD4(+)T-cell interaction with microglia. Furthermore, it appears that the anti-inflammatory T helper (Th) 2 CD4(+) T-cell subset is required in the facial nucleus, although the mechanism of CNS recruitment is not known. Pituitary adenylyl cyclase-activating polypeptide (PACAP) is a neuropeptide that has previously been demonstrated to be expressed by injured FMN. Interestingly, PACAP has been shown to act on peripheral macrophages by inducing chemokine expression capable of recruiting Th2 cells. Whether CNS-resident microglia, a related lineage to peripheral macrophages, respond to PACAP by expressing Th2-associated chemokines is not known. In this study, fluorescence-activated cell sorting was utilized to measure the frequency of microglia positive for different chemokines after exposure to various treatments. The results indicate that PACAP increases the frequency of microglia expressing Th2-associated chemokine, CCL11, and decreases the frequency of microglia expressing Th1-associated chemokine, CXCL11. In contrast, IFN-γ decreases the frequency of microglia expressing Th2-associated chemokine, CCL11, and increases the frequency of microglia expressing Th1-associated chemokine, CXCL11. Treatment with both PACAP and IFN-γ reversed the proinflammatory effect of IFN-γ. Given the recent focus on the therapeutic value of Th2 cells in the CNS during neurode-generative disease, PACAP may be a future therapeutic target for improving neuroregeneration after injury.