Thrombospondin-1 (TSP-1) is a major activator of latent transforming growth factor-␤ in vitro as well as in vivo.Mice deficient in TSP-1, despite appearing normal at birth, develop a chronic form of ocular surface disease that is marked by increased apoptosis and deterioration in the lacrimal gland, associated dysfunction, and development of inflammatory infiltrates that result in abnormal tears. The increase in CD4 ؉ T cells in the inflammatory infiltrates of the lacrimal gland, and the presence of anti-Sjögren's syndrome antigen A and anti-Sjögren's syndrome antigen B antibodies in the serum resemble autoimmune Sjögren's syndrome. These mice develop an ocular surface disorder dry eye that includes disruption of the corneal epithelial layer, corneal edema, and a significant decline in conjuctival goblet cells. Externally, several mice develop dry crusty eyes that eventually close. The inflammatory CD4 ؉ T cells detected in the lacrimal gland, as well as those in the periphery of older TSP-1 null mice, secrete interleukin-17A, a cytokine associated with chronic inflammatory diseases. Antigen-presenting cells, derived from TSP-1 null, but not from wild-type mice, activate T cells to promote the Th17 response. Together, these results indicate that TSP-1 deficiency results in a spontaneous form of chronic dry eye and aberrant histopathology associated with Sjögren's syndrome.

Certain forms of the heavy metals arsenic and chromium are considered human carcinogens, although they are believed to act through very different mechanisms. Chromium(VI) is believed to act as a classic genotoxic and mutagenic agent, and DNANchromatin appears to be the principal target for its effects. In contrast, arsenic(lll) is considered nongenotoxic, but is able to target specific cellular proteins, principally through sulfhydryl interactions. We had previously shown that various genotoxic chemical carcinogens, including chromium(VI), preferentially altered expression of several inducible genes but had little or no effect on constitutive gene expression. We were therefore interested in whether these carcinogenic heavy metals might target specific but distinct sites within cells, leading to alterations in gene expression that might contribute to the carcinogenic process. Arsenic(lll) and chromium(V1) each significantly altered both basal and hormone-inducible expression of a model inducible gene, phosphoenolpyruvate carboxykinase (PEPCK), at nonovertly toxic doses in the chick embryo in vivo and rat hepatoma H411E cells in culture. We have recently developed two parallel cell culture approaches for examining the molecular basis for these effects. First, we are examining the effects of heavy metals on expression and activation of specific transcription factors known to be involved in regulation of susceptible inducible genes, and have recently observed significant but different effects of arsenic(lll) and chromium(Vl) on nuclear transcription factor binding. Second, we have developed cell lines with stably integrated PEPCK promoter-luciferase reporter gene constructs to examine effects of heavy metals on promoter function, and have also recently seen profound effects induced by both chromium(V1) and arsenic(lil) in this system. These model systems should enable us to be able to identify the critical cis (DNA) and trans (protein) cellular targets of heavy metal exposure leading to alterations in expression of specific susceptible genes. It is anticipated that such information will provide valuable insight into the mechanistic basis for these effects as well as provide sensitive molecular biomarkers for evaluating human exposure. Environ Health Perspect 1 06(Suppl 4):1 005-1015 (1998). http://ehpnet1.niehs.nih.gov/docs/1998/Suppl4/ 1005-1015hamilton/abstract.html

APCs deployed within iris/ciliary body are responsible for promoting anterior chamber-associated immune deviation following injection of Ag into the eye. TGFβ-2, a constituent of the ocular microenvironment, converts conventional APCs that are pulsed with Ag into cells that induce immune deviation when injected into naive mice. TGFβ-2-treated APCs under-express IL-12 and CD40, and over-express active TGFβ. We have examined transcriptional changes within macrophage hybridoma no. 59, which promotes Th1 cell differentiation, and TGFβ-2-treated no. 59 as well as macrophage hybridoma no. 63, both of which induce immune deviation similar to anterior chamber-associated immune deviation. Immune deviation-inducing hybridomas up-regulated expression of thrombospondin, TGFβ, IFN-α and β, murine macrophage elastase, and macrophage-inflammatory protein-2 genes, while down-regulating expression of the genes for NF-κB and CD40. Based on the known properties of these gene products, a model is proposed in which these gene products, alone and through interacting signaling pathways, confer upon conventional APCs the capacity to create and surround themselves with an immunomodulatory microenvironment. The model proposes that the pleiotropic effects of thrombospondin are primarily responsible for creating this microenvironment that is stabile, rich in active TGFβ and IFN-α and β, deficient in IL-12, and chemoattractant via macrophage-inflammatory protein-2 for NK T cells. It is further proposed that presentation of Ag to T cells in this microenvironment leads to their differentiation into regulatory cells that suppress Th1 cell-dependent immunogenic inflammation.