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Streptococcus iniae is a Gram-positive bacterium and a severe pathogen to a wide range of economically important fish species. In addition, S. iniae is also a zoonotic pathogen and can cause serious infections in humans. In this study, we identified from a pathogenic S. iniae strain a putative bacteriocin, Sil, and examined its biological activity. Sil is composed of 101 amino acid residues and shares 35.6% overall sequence identity with the lactococcin 972 of Lactococcus lactis. Immunoblot analysis showed that Sil was secreted by S. iniae into the extracellular milieu. Purified recombinant Sil (rSil) exhibited a dose-dependent inhibitory effect on the growth of Bacillus subtilis but had no impact on the growths of other 16 Gram-positive bacteria and 10 Gram-negative bacteria representing 23 different bacterial species. Treatment of rSil by heating at 50°C abolished the activity of rSil. rSil bound to the surface of B. subtilis but induced no killing of the target cells. Cellular study revealed that rSil interacted with turbot (Scophthalmus maximus) head kidney monocytes and inhibited the innate immune response of the cells, which led to enhanced cellular infection of S. iniae. Antibody blocking of the extracellular Sil produced by S. iniae significantly attenuated the infectivity of S. iniae. Consistent with these in vitro observations, in vivo study showed that administration of turbot with rSil prior to S. iniae infection significantly increased bacterial dissemination and colonization in fish tissues. Taken together, these results indicate that Sil is a novel virulence-associated bacteriostatic and an immunoregulator that promotes S. iniae infection by impairing the immune defense of host fish. [ABSTRACT FROM AUTHOR]

Myelodysplastic syndrome (MDS) is a group of progressive,clonal, neoplastic bone marrow disorders characterized by hematopoietic stem cell dysregulation and abnormalities in the immune system. Mesenchymal stem cells (MSC) appear to modulate the immune system at the very first step of the immune response through the inhibition of dendritic cells (DCs) differentiation and maturation. However, it is still unclear whether the effects of MSC on the development of DCs will be altered with disease state. In addition, it is not clear whether there are differences in the effects between low-risk and high-risk MDS-MSC on DCs development. In this study, our data confirm that MDS-MSC mediate a potent inhibition of DCs differentiation. Additionaly, MDS-MSC greatly alter DCs functions, including endocytosis, IL-12 secretion, their ability to inhibit T cell proliferation. Moreover, our results show that there are major differences in DCs development and function between low-risk and high-risk MDS-MSC. Compared to high-risk MDS-MSC, low-risk MDS-MSC is characterized by a poor ability to inhibit DCs differentiation and maturation; and correspondingly, less dysfunctional DC endocytosis, mildly decreased IL-12 secretion, and a reduction in DC-mediated inhibition of T cell proliferation. Finally, our results demonstrate that MDS-MSC derived TGF-β1 is largely responsible for the inhitory effects. These results elucidate the different immunoregulatory role of MSC in low-risk and high-risk MDS on DCs development, which may be important for understanding the pathogenesis of MDS and the development of novel immune therapies for the treatment of MDS. [ABSTRACT FROM AUTHOR]