Mechanisms Involved in Type II Macrophage Activation and Effector Functions
Autoimmunities are extremely difficult to treat and involved in their pathogenesis are pro-inflammatory immune responses redirected against one's own tissues. Studies in our lab have shown macrophages that are induced to become type II macrophages protect against an animal model of MS, experimental autoimmune encephalomyelitis (EAE), with protection due to immune deviation. Another way to deviate immune responses away from inflammation is by infection with the parasitic helminth Schistosoma mansoni, which also protects against EAE. The contribution of type II macrophages in this protection is unknown, as are the mechanisms involved in promoting the phenotype induced by type II activation. This project investigates key mechanisms involved in type II activation, while also elucidating the possible effect of schistosome exposure on the induction of this activation state. Using a validated model of type II activation in vitro, we compared the effects of schistosome immune complexes on various macrophage properties such as cytokine, surface marker and enzymatic profiles. This thesis identified that exposure to schistosome complexes induces a macrophage state with characteristics of two distinct activation states (type II and alternative activation), as well as completely novel characteristics. This activation state shows many phenotypic properties associated with immune regulation, and may have important consequences for understanding mechanisms involved in protection against inflammatory illnesses. We also investigated key mechanisms involved in the anti-inflammatory responses induced by type II activation. Cytokine, chemokine and surface marker profiles of macrophages were assessed in response to type II activation in vitro, with the main emphasis on determining the effects of IL-10 and CD40 on the type II activation phenotype and function. This investigation found that type II activated macrophages depend on low levels of CD40/CD40L signalling to polarise Th2 development, as the expression of receptors for Th2-inducing cytokines are significantly impaired in the absence of this interaction. This suggests an important role for the low but maintained levels of CD40 on type II activated macrophages, in aiding the deviation of immune responses, while maintaining Th2 polarization. We also suggest a suppressive role of CD40/CD40L in IL-10 production, which is a novel find. The requirement of new treatments for MS is escalating as more people are affected each year. The impact of MS on the quality of life is severe and long lasting. Having a greater understanding of the mechanisms involved in deviating pro-inflammatory or anti-inflammatory responses will enable the development of much more effective treatments and therapies in the future.