Secretory phopholipase A2 is an enzyme that hydrolyses the Sn-2 ester bond of phospholipids, generating free fatty acids and lysophospholipids. Most secretory PLA2s are stored in cytoplasmic granules and are released in the extracellular environment on appropriate cell activation. Thus, they are present at higher concentration in the plasma and biologic fluids of patients with systemic inflammatory, autoimmune, or allergic disease, such as acute pancreatitis, rheumatoid arthritis, bronchial asthma, and allergic rhinitis. Also known as Lp-PLA2, PLA2G-VII is a plasma enzyme bound to lipoproteins: 80% bound to LDL, 15%-20% to HDL, and the remainder to VLDL (4-6). It is produced in major by mature macrophages and activated platelets. In contrast to other classical sPLA2s, PLA2G VII has poor specificity toward Sn-2 long chain fatty acids, unless heavily oxidized, and undergoes the catalysis of its substrates in the aqueous phase rather than at the interfacial surface of lipids. Thus, it has high specificity for water-soluble phospholipids in plasma including oxidatively modified phospholipids and platelet-activating factor (PAF). Because of the latter activity, it is also known as PAF acetylhydrolase (PAF-AH).
L-selectin (SELL) , also known as CD62L , is a key adhesion molecule that regulates both the migration of leukocytes at sites of inflammation and the recirculation of lymphocytes between blood and lymphoid tissues. It belongs to the selectin family of proteins , and consisting of a large , highly glycosylated , extracellular domain , a single spanning transmembrane domain and a small cytoplasmic tail. L-selectin is the only selectin expressed on leukocytes and mediates a number of leukocyte-endothelial interactions. L-selectin acts as a "homing receptor" for leukocytes to enter secondary lymphoid tissues via high endothelial venules. Ligands present on endothelial cells will bind to leukocyte expressing L-selectin , slowing leukocyte trafficking through the blood , and facilitating entry into a secondary lymphoid organ at that point. L-selectin-mediated lymphocyte recirculation is required for maintaining the appropriate tissue distribution of lymphocyte subpopulations including naïve and effector subsets such as regulatory T cells. In addition , L-selectin-mediated entry into peripheral lymph nodes is required for optimal induction of lymphocyte homeostatic proliferation during lymphopenia. Importantly , L-selectin has been shown to have both adhesive and signaling functions during leukocyte migration. L-selectin has also been shown to mediate leukocyte recruitment during chronic inflammatory and autoimmune diseases and thus is a potential therapeutic target for drug development.
LTBR (lymphotoxin beta receptor (TNFR superfamily, member 3)) is a member of the tumor necrosis factor (TNF) family of receptors. Tumor necrosis factor receptor is a trimeric cytokine receptor that binds tumor necrosis factors. The receptor cooperates with an adaptor protein (such as TRADD, TRAF, RIP), which is important in determining the outcome of the response. LTBR is expressed on the surface of most cell types, including cells of epithelial and myeloid lineages, but not on T and B lymphocytes. LTBR specifically binds the lymphotoxin membrane form (a complex of lymphotoxin-alpha and lymphtoxin-beta). LTBR and its ligand play a role in the development and organization of lymphoid tissue and tranformed cells. Activation of this protein can trigger apoptosis. Not only does the LTBR help trigger apoptosis, it can lead to the release of the cytokine interleukin 8. Overexpression of LTBR in HEK293 cells increases IL-8 promoter activity and leads to IL-8 release. It is also essential for development and organization of the secondary lymphoid organs and chemokine release.
Mannose-binding lectin (MBL), also named mannose or mannan-binding protein (MBP), is a C-type lectin which participates in the innate immune system as an activator of the complement system and as opsonin after binding to certain carbohydrate structures on microorganisms and pathogens. Its function appears to be pattern recognition in the first line of defense in the pre-immune host. MBL recognizes carbohydrate patterns found on the surface of a large number of pathogenic micro-organisms including bacteria, viruses, protozoa and fungi. Binding of MBL to a micro-organism results in activation of the lectin pathway of the complement system. Two forms of MBL, MBL-A and MBL-C, were characterized in rodents, rabbits, bovine and rhesus monkeys, whereas only one form was identified in humans, chimpanzees and chickens. The two forms are encoded by two distinct genes named MBL1 and MBL2, which have been identified in many species including the pig. The MBL1 and MBL2 genes encode mannan-binding lectins (MBL) A and C, respectively, that are collagenous lectins (collectins) produced mainly by the liver. The MBL1 gene encodes MBL-A, which has bacteria-binding properties in pigs and rodents but is mutated to a pseudogene in humans and chimpanzees. Deficiency of MBL is probably the most common human immunodeficiency and is associated with an increased risk of mucosally acquired infections including meningococcal disease. MBL could modify disease susceptibility by modulating macrophage interactions with mucosal organisms at the site of initial acquisition.
The chemokine (C-C motif) ligand 2 (CCL2), also known as monocyte chemoattractant protein (MCP)-1 and small inducible cytokine A2 (SCYA2)), is a small cytokine that belongs to the CC chemokine family responsible for monocyte attraction. Its cognate receptor, CCR2, play a critical role in regulating nociceptive processes during neuropathic pain. Both CCL2 and CCR2 are implicated in induction of autoimmunity. CCL2 recruits monocytes, memory T cells, and dendritic cells to the sites of inflammation produced by either tissue injury or infection. Recently research also showed that CCL2 might be useful as a biomarker of fibrosis as well as a target for therapeutic intervention.
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