NAD-dependent ADP-ribosylation of the human antimicrobial and immune-modulatory peptide LL-37 by ADP-ribosyltransferase-1

LL-37 is a cationic peptide belonging to the cathelicidin family that has antimicrobial and immune-modulatory properties. Here we show that the mammalian mono-ADP-ribosyltransferase-1 (ART1), which selectively transfers the ADP-ribose moiety from NAD to arginine residues, ADP-ribosylates LL-37 in vitro. The incorporation of ADP-ribose was first observed by Western blot analysis and then confirmed by MALDI-TOF. Mass-spectrometry showed that up to four of the five arginine residues present in LL-37 could be ADP-ribosylated on the same peptide when incubated at a high NAD concentration in the presence of ART1. The attachment of negatively charged ADP-ribose moieties considerably alters the positive charge of the arginine residues thus reducing the cationicity of LL-37. The cationic nature of LL-37 is key for its ability to interact with cell membranes or negatively charged biomolecules, such as DNA, RNA, F-actin and glycosaminoglycans. Thus, the ADP-ribosylation of LL-37 is expected to have the potential to modulate LL-37 biological activities in several physiological and pathological settings

Helicobacter pylori Induces Activation of Human Peripheral γδ+ T Lymphocytes

Helicobacter pylori is a Gram-negative bacterium that causes gastric and duodenal diseases in humans. Despite a robust antibody and cellular immune response, H. pylori infection persists chronically. To understand if and how H. pylori could modulate T cell activation, in the present study we investigated in vitro the interaction between H. pylori and human T lymphocytes freshly isolated from peripheral blood of H. pylori-negative donors. A direct interaction of live, but not killed bacteria with purified CD3+ T lymphocytes was observed by microscopy and confirmed by flow cytometry. Live H. pylori activated CD3+ T lymphocytes and predominantly γδ+ T cells bearing the TCR chain Vδ2. Upon interaction with H. pylori, these cells up-regulated the activation molecule CD69 and produced cytokines (such as TNFα, IFNγ) and chemokines (such as MIP-1β, RANTES) in a non-antigen-specific manner. This activation required viable H. pylori and was not exhibited by other Gram-negative bacteria. The cytotoxin-associated antigen-A (CagA), was at least partially responsible of this activation. Our results suggest that H. pylori can directly interact with T cells and modulate the response of γδ+ T cells, thereby favouring an inflammatory environment which can contribute to the chronic persistence of the bacteria and eventually to the gastric pathology

Coligation of the hepatitis C virus receptor CD81 with CD28 primes naive T lymphocytes to acquire type 2 effector function.

Costimuli provide supplementary signals required by naive T cells to become fully activated upon Ag encounter. Tetraspanins are a large family of transmembrane proteins that can costimulate T cells when engaged in vitro. In this study, we describe for the first time that coligation of the tetraspanins CD81, CD82, or CD9 with the costimulatory molecule CD28 in vitro leads to proliferation of naive T cells. When activated through this pathway, both CD4+ and CD8+ naive T cells differentiate into type 2 effector cells, which produce IL-4, IL-5, IL-13, and IL-10, together with IL-2 and TNF-alpha, but little to no IFN-gamma. These effector cells descend from precursors that display early and strong production of IL-4, STAT6 phosphorylation, and up-regulation of the transcription factor GATA-3, suggesting a direct skewing toward Th2 differentiation without a Th0 intermediate. The hepatitis C virus envelope protein E2 is the only ligand known for CD81. Therefore, we propose that this new type of Ag-independent T cell activation may occur in hepatitis C virus-infected individuals, contributing to liver inflammation, impaired type 1 immune responses, and recurrent flares of type 2 immunity associated with chronic infection

CIS Associates with the Interleukin-2 Receptor β Chain and Inhibits Interleukin-2-dependent Signaling

CIS is a cytokine-inducedSH2-containing protein that was originally cloned as an interleukin (IL)-3-inducible gene. CIS is known to associate with the IL-3 receptor β chain and erythropoietin receptor and to inhibit signaling mediated by IL-3 and erythropoietin. We now demonstrate that CIS also interacts with the IL-2 receptor β chain (IL-2Rβ). This interaction requires the A region of IL-2Rβ (residues 313–382), which also mediates the association of IL-2Rβ with Lck and Jak3. Correspondingly, CIS inhibits functions associated with both of these kinases: Lck-mediated phosphorylation of IL-2Rβ and IL-2-mediated activation of Stat5. Thus, we demonstrate that CIS can negatively control at least two independent IL-2 signaling pathways. Although a functional SH2 binding domain of CIS was not required for its interaction with IL-2Rβ in vitro, its phosphotyrosine binding capability was essential for the inhibitory action of CIS. On this basis, we have generated a mutant form of CIS protein with an altered SH2 domain that acts as a dominant negative and should prove useful in further understanding CIS action

Small molecule Toll-like receptor 7 agonists localize to the MHC class II loading compartment of human plasmacytoid dendritic cells

Toll-like receptors (TLRs) 7 and 8 are intracellular sensors activated by single stranded RNA species generated during viral infections. Various synthetic small molecules can also activate TLR7 and/or 8; however the molecular mechanisms governing their TLR7/8 triggering remain largely unknown. To shed light on how small molecule agonists target TLRs, we labeled two imidazoquinolines, resiquimod and imiquimod, and one purine-like compound, SM360320, with two different fluorophores (TAMRA and AlexaFluor488) and monitored their intracellular localization in human plasmacytoid dendritic cells (pDCs). All fluorescent compounds induced the production of IFN TNF and IL-6 and the up-regulation of CD80 and CD86 by pDCs showing they retained TLR7 stimulating activity. Confocal imaging demonstrated that all compounds concentrated in LAMP1+CD63+HLA-DR+ endosomes, which represent the MHC class II loading compartment of pDCs. Moreover, CpG-B, which triggers TLR9 signaling from this endolysosomal compartment, co-localized with all 3 TLR7/8 small molecule agonists. By contrast, treatment of pDCs with bafilomycin A, an antagonist of the vacuolar-type proton ATPase that inhibits TLR7 and TLR9 signaling, prevented the accumulation of imiquimod-TAMRA, but not of CpG-B-TAMRA, in LAMP1+HLA-DR+ endosomes. These results indicate that a pH-driven concentration of small molecule TLR7 agonists in the MHC class II loading compartment is required for pDCs activation