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The natural killer group 2 member D (NKG2D) receptor is a C-type lectin-like activating receptor mainly expressed by cytotoxic immune cells including NK, CD8 + T, γδ T and NKT cells and in some pathological conditions by a subset of CD4 + T cells. It binds a variety of ligands (NKG2DL) whose expressions is finely regulated by stress-related conditions. The NKG2DL/NKG2D axis plays a central and complex role in the regulation of immune responses against diverse cellular threats such as oncogene-mediated transformations or infections. We generated a panel of seven highly specific anti-human NKG2D single-domain antibodies targeting various epitopes. These single-domain antibodies were integrated into bivalent and bispecific antibodies using a versatile plug-and-play Fab-like format. Depending on the context, these Fab-like antibodies exhibited activating or inhibitory effects on the immune response mediated by the NKG2DL/NKG2D axis. In solution, the bivalent anti-NKG2D antibodies that compete with NKG2DL potently blocked the activation of NK cells seeded on immobilized MICA, thus constituting antagonizing candidates. Bispecific anti-NKG2DxHER2 antibodies that concomitantly engage HER2 on tumor cells and NKG2D on NK cells elicited cytotoxicity of unstimulated NK in a tumor-specific manner, regardless of their apparent affinities and epitopes. Importantly, the bispecific antibodies that do not compete with ligands binding retained their full cytotoxic activity in the presence of ligands, a valuable property to circumvent immunosuppressive effects induced by soluble ligands in the microenvironment., (© 2020 The Author(s). Published with license by Taylor & Francis Group, LLC.)

The genome of Pseudomonas aeruginosa PAO1 contains three type VI secretion systems (T6SSs) called H1-, H2-, and H3-T6SS. The H1-T6SS secretes three identified toxins that target other bacteria, providing a fitness advantage for P. aeruginosa, and likely contributes to bacterial pathogenesis in chronic infections. However, no specific substrates or defined roles have been described for the two other systems. Here, we demonstrate that the expression of H2-T6SS genes of strain PAO1 is up-regulated during the transition from exponential to stationary phase growth and regulated by the Las and Rhl quorum sensing systems. In addition, we identify two putative Fur boxes in the promoter region and find that H2-T6SS transcription is negatively regulated by iron. We also show that the H2-T6SS system enhances bacterial uptake into HeLa cells (75% decrease in internalization with a H2-T6SS mutant) and into lung epithelial cells through a phosphatidylinositol 3-kinase-dependent pathway that induces Akt activation in the host cell (50% decrease in Akt phosphorylation). Finally, we show that H2-T6SS plays a role in P. aeruginosa virulence in the worm model. Thus, in contrast to H1-T6SS, H2-T6SS modulates interaction with eukaryotic host cells. Together, T6SS can carry out different functions that may be important in establishing chronic P. aeruginosa infections in the human host.

Bacterial pathogenesis often depends on regulatory networks, two-component systems and small RNAs (sRNAs). In Pseudomonas aeruginosa, the RetS sensor pathway downregulates expression of two sRNAs, rsmY and rsmZ. Consequently, biofilm and the Type Six Secretion System (T6SS) are repressed, whereas the Type III Secretion System (T3SS) is activated. We show that the HptB signalling pathway controls biofilm and T3SS, and fine-tunes P. aeruginosa pathogenesis. We demonstrate that RetS and HptB intersect at the GacA response regulator, which directly controls sRNAs production. Importantly, RetS controls both sRNAs, whereas HptB exclusively regulates rsmY expression. We reveal that HptB signalling is a complex regulatory cascade. This cascade involves a response regulator, with an output domain belonging to the phosphatase 2C family, and likely an anti-anti-sigma factor. This reveals that the initial input in the Gac system comes from several signalling pathways, and the final output is adjusted by a differential control on rsmY and rsmZ. This is exemplified by the RetS-dependent but HptB-independent control on T6SS. We also demonstrate a redundant action of the two sRNAs on T3SS gene expression, while the impact on pel gene expression is additive. These features underpin a novel mechanism in the fine-tuned regulation of gene expression.

Bacterial attachment to the substratum involves several cell surface organelles, including various types of pili. The Pseudomonas aeruginosa Tad machine assembles type IVb pili, which are required for adhesion to abiotic surfaces and to eukaryotic cells. Type IVb pili consist of a major subunit, the Flp pilin, processed by the FppA prepilin peptidase. In this study, we investigated the regulatory mechanism of the tad locus. We showed that the flp gene is expressed late in the stationary growth phase in aerobic conditions. We also showed that the tad locus was composed of five independent transcriptional units. We used transcriptional fusions to show that tad gene expression was positively controlled by the PprB response regulator. We subsequently showed that PprB bound to the promoter regions, directly controlling the expression of these genes. We then evaluated the contribution of two genes, tadF and rcpC, to type IVb pilus assembly. The deletion of these two genes had no effect on Flp production, pilus assembly, or Flp-mediated adhesion to abiotic surfaces in our conditions. However, our results suggest that the putative RcpC protein modifies the Flp pilin, thereby promoting Flp-dependent adhesion to eukaryotic cells.

Pseudomonas aeruginosa is an opportunistic pathogen involved in several diseases, including cystic fibrosis and nosocomial infections. Although the behavior of this bacterium at 37 degrees C has been intensively studied, little is known about its capacity to adapt and survive at suboptimal temperatures, such as those encountered in hospitals. In this work, transcriptomic and proteomic analyses were used to identify factors that allow P. aeruginosa to become established at room temperature (close to 25 degrees C) and thus facilitate host infections. Since the virulence of this pathogen is multifactorial and dependent on the extracellular release of toxins and degradative enzymes targeted to the host by several secretory systems, the study focused on genes activated at 25 degrees C, namely, those encoding either components of the secretory machinery or secreted proteins. These observations were enhanced by 2D-PAGE analyses, which showed that the production of effectors from type I and type II secretion systems (respectively, proteases AprA and PrpL) and of a hemolysin co-regulated protein (Hcp) related to the type VI secretion system was specifically stimulated when the growth temperature was lowered from 37 to 25 degrees C. The results provide a fundamental basis for investigating the processes that allow P. aeruginosa to adapt to suboptimal growth temperatures and which thereby promote nosocomial infection.

Although preB cell-receptor (pre-BCR) formation and cell-surface expression is essential for B cell development, pre-BCR generation of signal transduction remains elusive. Here, we report that recombinant pre-BCRs and the surrogate light chain bind specifically to the bone marrow stromal cell galectin-1 (GAL1), an S-type lectin. The surrogate light chain/GAL1 association is a direct protein-protein interaction (K(a) = 2 x 10(6) M(-1)), and the NH(2) extra loop of lambda-like is the major binding element. Pre-BCR binding to stromal cells depends upon GAL1 anchoring to glycosylated counter-receptors, and these complexes completely relocalize to form a synapse at the contact zone between preB and stromal cells. This immune developmental synapse is accompanied by the initiation of intracellular tyrosine kinase activity and signal transduction from the pre-BCR.