γδ T cells, αβ T cells, and B cells are present together in all but the most primitive vertebrates, suggesting that each population contributes to host immune competence uniquely and that all three are necessary for maintaining immune competence. Functional and molecular analyses indicate that in infections, γδ T cells respond earlier than αβ T cells do and that they emerge late after pathogen numbers start to decline. Thus, these cells may be involved in both establishing and regulating the inflammatory response. Moreover, γδ T cells and αβ T cells are clearly distinct in their antigen recognition and activation requirements as well as in the development of their antigen-specific repertoire and effector function. These aspects allow γδ T cells to occupy unique temporal and functional niches in host immune defense. We review these and other advances in γδ T cell biology in the context of their being the major initial IL-17 producers in acute infection.

Pigment epithelium-derived factor (PEDF) is an extracellular multifunctional protein belonging to the serpin superfamily with demonstrable neurotrophic, gliastatic, neuronotrophic, antiangiogenic, and antitumorigenic properties. We have previously provided biochemical evidence for high affinity PEDFbinding sites and proteins in plasma membranes of retina, retinoblastoma, and CNS cells. This study was designed to reveal a receptor involved in the biological activities of PEDF. Using a yeast two-hybrid screening, we identified a novel gene from pigment epithelium of the human retina that codes for a PEDFbinding partner, which we term PEDF-R. The derived polypeptide has putative transmembrane, intracellular and extracellular regions, and a phospholipase domain. Recently, PEDF-R (TTS-2.2/independent phospholipase A 2 (PLA 2 ) and mouse desnutrin/ATGL) has been described in adipose cells as a member of the new calcium-independent PLA 2 /nutrin/patatin-like phospholipase domain-containing 2 (PNPLA2) family that possesses triglyceride lipase and acylglycerol transacylase activities. Here we describe the PEDF-R gene expression in the retina and its heterologous expression by bacterial and eukaryotic systems, and we demonstrate that its protein product has specific and high binding affinity for PEDF, has a potent phospholipase A 2 activity that liberates fatty acids, and is associated with eukaryotic cell membranes. Most importantly, PEDF binding stimulates the enzymatic phospholipase A 2 activity of PEDF-R. In conclusion, we have identified a novel PEDF-R gene in the retina for a phospholipase-linked membrane protein with high affinity for PEDF, suggesting a molecular pathway by which ligand/receptor interaction on the cell surface could generate a cellular signal.

Pigment epithelium-derived factor (PEDF), a neurotrophic and antiangiogenic serpin, is identified in tissues rich in collagen, e.g. cornea, vitreous, bone, and cartilage. We show that recombinant human PEDF formed complexes with collagens from the bovine cornea and vitreous. We have examined the direct binding of PEDF to collagen I and found that interactions were ionic in nature and occurred when PEDF and collagen I were both in solution, when either one was immobilized, or even when collagen I was denatured under reducing conditions. 125 Pigment epithelium-derived factor (PEDF) 1 is an extracellular protein that has neurotrophic and antiangiogenic activities expressed mainly in compartments of the eye. It acts in neuronal survival and differentiation on photoreceptor cells and on neuronal cells of the retina and central nervous system (1-5). Several reports show that PEDF is a major inhibitor of neovascularization and is responsible for excluding vessels from invading the cornea, vitreous, and retina (6 -8). These biological activities are of great importance for the development, morphology, and vision process in the eye.PEDF is highly secreted by a variety of cells and associates intimately with extracellular matrix (5, 9 -12). In particular, cells of the retinal pigment epithelium secrete PEDF protein, which associates with the interphotoreceptor matrix consistent with its affinity for binding glycosaminoglycans, e.g. heparin and heparan sulfate (13,14). Other areas in the eye that contain PEDF include the vitreous gel and the cornea. In the bovine vitreous, PEDF accumulates at 20 nM accounting for Ͻ1% of the total protein of cell-free extracts (15). In the human cornea, PEDF immunolabeling has been detected in the epithelium and endothelium (16). Outside of the eye, PEDF has been detected in teeth, bone, and cartilage matrix (10). It is worth noting that in addition to containing PEDF and being rich in collagen, the adult vitreous, cornea, and bone and cartilage matrixes are vessel-free.Collagens comprise a family of 19 proteins with a broad range of structural and physiological functions, which are strictly located in the extracellular space. They are composed of three chains that fold to form at least one triple helical domain. All collagens are present in tissues as homotrimeric and/or heterotrimeric assemblies and have specific tissue distributions and functions, e.g. they are involved in hemostasis, wound healing, cell adhesion, and migration. In the cornea and vitreous they are known to give transparency, strength, and elasticity. Collagen type I is the major protein of the cornea (94% of the total collagen in the bovine cornea) and coassembles in heterotypic fibrils with collagen type V. Collagen type II is the main protein of the vitreous (70 -80%) followed by collagens type V/XI and IX (17).Studies on structure-function relationships have revealed that PEDF is a glycoprotein of 50 kDa that folds like members of the superfamily of serine protease inhibitors (serpins) (13,18,19), but its neurotroph...

No abstract