Vascular endothelial growth factor receptor‐3 (VEGFR‐3/Flt4) binds two known members of the VEGF ligand family, VEGF‐C and VEGF‐D, and has a critical function in the remodelling of the primary capillary vasculature of midgestation embryos. Later during development, VEGFR‐3 regulates the growth and maintenance of the lymphatic vessels. In the present study, we have isolated and cultured stable lineages of blood vascular and lymphatic endothelial cells from human primary microvascular endothelium by using antibodies against the extracellular domain of VEGFR‐3. We show that VEGFR‐3 stimulation alone protects the lymphatic endothelial cells from serum deprivation‐induced apoptosis and induces their growth and migration. At least some of these signals are transduced via a protein kinase C‐dependent activation of the p42/p44 MAPK signalling cascade and via a wortmannin‐sensitive induction of Akt phosphorylation. These results define the critical role of VEGF‐C/VEGFR‐3 signalling in the growth and survival of lymphatic endothelial cells. The culture of isolated lymphatic endothelial cells should now allow further studies of the molecular properties of these cells.

Orf virus, a member of the poxvirus family, produces a pustular dermatitis in sheep, goats, and humans. The lesions induced after infection with orf virus show extensive proliferation of vascular endothelial cells, dilation of blood vessels and dermal swelling. An explanation for the nature of these lesions may lie in the discovery that orf virus encodes an apparent homolog of the mammalian vascular endothelial growth factor (VEGF) family of molecules. These molecules mediate endothelial cell proliferation, vascular permeability, angiogenesis, and lymphangiogenesis via the endothelial cell receptors VEGFR-1 (Flt1), VEGFR-2 (KDR/Flk1), and VEGFR-3 (Flt4). The VEGF-like protein of orf virus strain NZ2 (ORFV2-VEGF) is most closely related in primary structure to VEGF. In this study we examined the biological activities and receptor specificity of the ORFV2-VEGF protein. ORFV2-VEGF was found to be a disulfide-linked homodimer with a subunit of ≈25 kDa. ORFV2-VEGF showed mitogenic activity on bovine aortic and human microvascular endothelial cells and induced vascular permeability. ORFV2-VEGF was found to bind and induce autophosphorylation of VEGFR-2 and was unable to bind or activate VEGFR-1 and VEGFR-3, but bound the newly identified VEGF ₁₆₅ receptor neuropilin-1. These results indicate that, from a functional viewpoint, ORFV2-VEGF is indeed a member of the VEGF family of molecules, but is unique, however, in that it utilizes only VEGFR-2 and neuropilin-1.

Orf virus is the type species of the Parapoxvirus genus of the family Poxviridae. It induces acute pustular skin lesions in sheep and goats and is transmissible to humans. The genome is G+C rich, 138 kbp and encodes 132 genes. It shares many essential genes with vaccinia virus that are required for survival but encodes a number of unique factors that allow it to replicate in the highly specific immune environment of skin. Phylogenetic analysis suggests that both viral interleukin-10 and vascular endothelial growth factor genes have been “captured” from their host during the evolution of the parapoxviruses. Genes such as a chemokine binding protein and a protein that binds granulocyte-macrophage colony-stimulating factor and interleukin-2 appear to have evolved from a common poxvirus ancestral gene while three parapoxvirus nuclear factor (NF)-κB signalling pathway inhibitors have no homology to other known NF-κB inhibitors. A homologue of an anaphase-promoting complex subunit that is believed to manipulate the cell cycle and enhance viral DNA synthesis appears to be a specific adaptation for viral-replication in keratinocytes. The review focuses on the unique genes of orf virus, discusses their evolutionary origins and their role in allowing viral-replication in the skin epidermis.

Poxviridae is a family of enveloped, brick-shaped or ovoid viruses. The genome is a linear molecule of dsDNA (128–375 kbp) with covalently closed ends. The family includes the sub-families Entomopoxvirinae, whose members have been found in four orders of insects, and Chordopoxvirinae, whose members are found in mammals, birds, reptiles and fish. Poxviruses are important pathogens in various animals, including humans, and typically result in the formation of lesions, skin nodules, or disseminated rash. Infections can be fatal. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Poxviridae, which is available at ictv.global/report/poxviridae.

Many burn interventions aim to target the inflammatory response as a means of enhancing healing or limiting hypertrophic scarring. Murine models of human burns have been developed, but the inflammatory response to injury in these models has not been well defined. The aim of this study was to profile inflammatory cell populations and gene expression relative to healing and scarring in a murine model of thermal burns. Cutaneous injuries were created on the dorsal region of C57Bl/6 mice using a heated metal rod. Animals were euthanized at selected time points over ten weeks, with the lesions evaluated using macroscopic measurements, histology, immunofluorescent histochemistry and quantitative PCR. The burn method generated a reproducible, partial-thickness injury that healed within two weeks through both contraction and re-epithelialization, in a manner similar to human burns. The injury caused an immediate increase in pro-inflammatory cytokine and chemokine expression, coinciding with an influx of neutrophils, and the disappearance of Langerhans cells and mast cells. This preceded an influx of dendritic cells and macrophages, a quarter of which displayed an inflammatory (M1) phenotype, with both populations peaking at closure. As with human burns, the residual scar increased in size, epidermal and dermal thickness, and mast cell numbers over 10 weeks, but abnormal collagen I-collagen III ratios, fibre organization and macrophage populations resolved 3–4 weeks after closure. Characterisation of the inflammatory response in this promising murine burn model will assist future studies of burn complications and aid in the preclinical testing of new anti-inflammatory and anti-scarring therapies.

Vascular endothelial growth factor (VEGF)-A, a key regulator of cutaneous blood vessel formation, appears to have an additional role during wound healing, enhancing re-epithelialization. Orf virus, a zoonotic parapoxvirus, induces proliferative skin lesions that initiate in wounds and are characterized by extensive blood vessel formation, epidermal hyperplasia and rete ridge formation. The vascular changes beneath the lesion are largely due to viral-expressed VEGF-E. This study investigated using mouse skin models whether VEGF-E can induce epidermal changes such as that seen in the viral lesion. Injection of VEGF-E into normal skin increased the number of endothelial cells and blood vessels within the dermis and increased epidermal thickening and keratinocyte number. Injection of VEGF-E into wounded skin, which more closely mimics orf virus lesions, increased neo-epidermal thickness and area, promoted rete ridge formation, and enhanced wound re-epithelialization. Quantitative RT-PCR analysis showed that VEGF-E did not induce expression of epidermal-specific growth factors within the wound, but did increase matrix metalloproteinase (MMP)-2 and MMP-9 expression. In cell-based assays, VEGF-E induced keratinocyte migration and proliferation, responses that were inhibited by a neutralizing antibody against VEGF receptor (VEGFR)-2. These findings demonstrate that VEGF-E, both directly and indirectly, regulates keratinocyte function, thereby promoting epidermal regeneration.