Activation of innate immune response in human macrophages by Herpes simplex virus-1 and crystallized monosodium urate

Innate immunity provides the first line of defence against invading pathogens, and can also be activated by endogenous danger signals released upon tissue damage or injury. Macrophages play an important role in innate immunity. They perform the immune surveillance of their immediate surroundings seeking out tissue damage and/or invading pathogens via pattern recognition receptors. Macrophages are activated upon detection of an invading pathogen or tissue damage, leading to the expression, and secretion of the proteins required for an efficient innate immune response. Herpes simplex virus-1 (HSV-1) is a common human pathogen. It is a master of evading the host immune response leading to its ability to cause a life-long infection in its host. In most cases, HSV-1 does not cause any symptoms in the host, or causes nothing more than an occasional painful blister in the orofacial region. However, in certain cases when the host immune system is compromised, it can cause severe, even lethal, infections. Uric acid can act as an endogenous danger signal that cells can produce and release into the extracellular space after encountering a stress, including that caused by certain viral infections. A high amount of uric acid in cells can also be attributed to certain dietary habits. In the extracellular space if present at high enough concentrations and in the presence of sodium, uric acid can become crystallized into monosodium urate (MSU). MSU is the causative of gouty inflammation in the joints and is known to be phagocytosed by macrophages. In this work, human monocyte-derived macrophages infected with HSV-1, or stimulated with MSU were studied using several proteomic methods combined with functional assays. The main goals were: to characterize the protein secretion pathways and the proteins being secreted from macrophages upon (1) HSV-1 infection, and (2) MSU stimulation; and (3) to characterize the functional mechanisms of HSV-1 infected cell protein 27 (ICP27) in the inhibition of the interferon (IFN) response and also inhibition of apoptosis during HSV-1 infection. The results revealed that robust extracellular vesicle-mediated unconventional protein secretion is induced by IFN-b priming in HSV-1-infected, and by MSU stimulation in Toll-like receptor 4 ligand, bacterial cell wall component lipopolysaccharide-primed human macrophages. The secreted proteins included endogenous danger signal proteins, and interferon-stimulated gene-encoded proteins. In addition, HSV-1 ICP27 protein requires both the nuclear localization sequence (NLS) and nuclear export sequence (NES) in order to inhibit the IFN response, whereas the NES, but not NLS, is required for the inhibition of apoptosis. The results also demonstrate that pattern recognition receptors RIG-I and/or MDA5 are involved in the HSV-1-induced activation of apoptosis. To conclude, this thesis provides new information on the innate immune response induced by HSV-1 infection, and MSU stimulation, and also on the evasion mechanisms deployed by HSV-1 to avoid the innate immune response in human macrophages. These new results presented in this thesis may be exploited in several ways; in the development of new therapies against viral infections, and in the treatment of autoinflammatory diseases.