NF-κB. Activity in granuloma formation A granuloma is the body's way of dealing with a substance it cannot remove or sterilize. Infectious causes of granulomas (infections are typically the most common cause of granulomas) include tuberculosis, leprosy, histoplasmosis, cryptococcosis, coccidioidomycosis, blastomycosis, and toxoplasmosis. Examples of non-infectious granulomatous diseases are sarcoidosis, Crohn's disease, berylliosis, giant-cell arteritis, granulomatosis with polyangiitis, eosinophilic granulomatosis with polyangiitis, pulmonary rheumatoid nodules, and aspiration of food and other particulate material into the lung. The infectious pathophysiology of granulomas is discussed primarily here. The key association between IFN-γ and granulomas is that IFN-γ activates macrophages so that they become more powerful in killing intracellular organisms. Activation of macrophages by IFN-γ from Th1 helper cells in mycobacterial infections allows the macrophages to overcome the inhibition of phagolysosome maturation caused by mycobacteria (to stay alive inside macrophages). The first steps in IFN-γ-induced granuloma formation are activation of Th1 helper cells by macrophages releasing IL-1 and IL-12 in the presence of intracellular pathogens, and presentation of antigens from those pathogens. Next the Th1 helper cells aggregate around the macrophages and release IFN-γ, which activates the macrophages. Further activation of macrophages causes a cycle of further killing of intracellular bacteria, and further presentation of antigens to Th1 helper cells with further release of IFN-γ. Finally, macrophages surround the Th1 helper cells and become fibroblast-like cells walling off the infection. Activity during pregnancy Uterine Natural Killer cells (NK) secrete high levels of chemoattractants, such as IFN-γ in mice. IFN-γ dilates and thins the walls of maternal spiral arteries to enhance blood flow to the implantation site. This remodeling aids in the development of the placenta as it invades the uterus in its quest for nutrients. IFN-γ knockout mice fail to initiate normal pregnancy-induced modification of decidual arteries. These models display abnormally low amounts of cells or necrosis of decidua. In humans, elevated levels of IFN-γ have been associated with increased risk of miscarriage. Correlation studies have observed high IFN-γ levels in women with a history of spontaneous miscarriage, when compared to women with no history of spontaneous miscarriage. Additionally, low-IFN-γ levels are associated with women who successfully carry to term. It is possible that IFN-γ is cytotoxic to trophoblasts, which leads to miscarriage. However, causal research on the relationship between IFN-γ and miscarriage has not been performed due to ethical constraints. Production Recombinant human IFN-γ, as an expensive biopharmaceutical, has been expressed in