Regulation of Immune Function by the Lymphatic System in Lymphedema.

The lymphatic vasculature has traditionally been thought to play a passive role in the regulation of immune responses by transporting antigen presenting cells and soluble antigens to regional lymph nodes. However, more recent studies have shown that lymphatic endothelial cells regulate immune responses more directly by modulating entry of immune cells into lymphatic capillaries, presenting antigens on major histocompatibility complex proteins, and modulating antigen presenting cells. Secondary lymphedema is a disease that develops when the lymphatic system is injured during surgical treatment of cancers or is damaged by infections. We have used mouse models of lymphedema in order to understand the effects of chronic lymphatic injury on immune responses and have shown that lymphedema results in a mixed T helper cell and T regulatory cell (Treg) inflammatory response. Prolonged T helper 2 biased immune responses in lymphedema regulate the pathology of this disease by promoting tissue fibrosis, inhibiting formation of collateral lymphatics, decreasing lymphatic vessel pumping capacity, and increasing lymphatic leakiness. Treg infiltration following lymphatic injury results from proliferation of natural Tregs and suppresses innate and adaptive immune responses. These studies have broad clinical relevance since understanding how lymphatic injury in lymphedema can modulate immune responses may provide a template with which we can study more subtle forms of lymphatic injury that may occur in physiologic conditions such as aging, obesity, metabolic tumors, and in the tumor microenvironment.

Allergens produce serine proteases-dependent distinct release of metabolite DAMPs in human bronchial epithelial cells.

BACKGROUND: The respiratory epithelium is a major site for disease interaction with inhaled allergens. Additional to IgE-dependent effects, allergens contain proteases that may stimulate human bronchial epithelial cells (HBECs) through protease-activated receptors, causing the release of mediators important in driving Th2-mediated immune responses. OBJECTIVE: We aimed to investigate whether different allergens induce metabolite DAMPs such as ATP and uric acid (UA) release in HBECs. METHODS: HBECs (BEAS-2B cell line) were exposed to different allergen extracts; house dust mite (HDM), Alternaria alternata, Artemisia vulgaris and Betula pendula and UA, ATP, IL-8 and IL-33 release were measured. Allergen extracts were heat-inactivated or pre-incubated with serine (AEBSF) or cysteine (E64) protease inhibitors to study the involvement of protease activity in ATP, UA and IL-8 release. HDM-induced release of UA was studied in a mouse model of allergic inflammation. RESULTS: All allergens caused dose-dependent rapid release of ATP and IL-8, but only HDM induced UA release from HBECs. HDM also caused release of UA in vivo in our mouse model of allergic inflammation. ATP release by all 4 allergen extracts was significantly reduced by heat-inactivation and by serine protease inhibitors. Similarly, the HDM-induced UA release was also abrogated by heat-inactivation of HDM extract and dependent on serine proteases. Furthermore, allergen-induced IL-8 mRNA expression was inhibited by serine protease inhibitors. CONCLUSIONS AND CLINICAL RELEVANCE: ATP was released by all 4 allergens in HBECs supporting the role of ATP involvement in asthma pathology. However, HDM stands out by its capacity to cause UA release, which is of interest in view of the proposed role of UA in early initiation of allergic asthma. Although serine proteases may be involved in the activity of all the studied allergens, further work is warranted to explain the differences between HDM and the other 3 allergens regarding the effects on UA release.

High-throughput proteomics reveal alarmins as amplifiers of tissue pathology and inflammation after spinal cord injury.

Spinal cord injury is characterized by acute cellular and axonal damage followed by aggressive inflammation and pathological tissue remodelling. The biological mediators underlying these processes are still largely unknown. Here we apply an innovative proteomics approach targeting the enriched extracellular proteome after spinal cord injury for the first time. Proteomics revealed multiple matrix proteins not previously associated with injured spinal tissue, including small proteoglycans involved in cell-matrix adhesion and collagen fibrillogenesis. Network analysis of transcriptomics and proteomics datasets uncovered persistent overexpression of extracellular alarmins that can trigger inflammation via pattern recognition receptors. In mechanistic experiments, inhibition of toll-like receptor-4 (TLR4) and the receptor for advanced glycation end-products (RAGE) revealed the involvement of alarmins in inflammatory gene expression, which was found to be dominated by IL1 and NFκΒ signalling. Extracellular high-mobility group box-1 (HMGB1) was identified as the likely endogenous regulator of IL1 expression after injury. These data reveal a novel tissue remodelling signature and identify endogenous alarmins as amplifiers of the inflammatory response that promotes tissue pathology and impedes neuronal repair after spinal cord injury.