PD-L1 signaling on human memory CD4+ T cells induces a regulatory phenotype

Programmed cell death protein 1 (PD-1) is expressed on T cells upon T cell receptor (TCR) stimulation. PD-1 ligand 1 (PD-L1) is expressed in most tumor environments, and its binding to PD-1 on T cells drives them to apoptosis or into a regulatory phenotype. The fact that PD-L1 itself is also expressed on T cells upon activation has been largely neglected. Here, we demonstrate that PD-L1 ligation on human CD25-depleted CD4⁺ T cells, combined with CD3/TCR stimulation, induces their conversion into highly suppressive T cells. Furthermore, this effect was most prominent in memory (CD45RA⁻CD45RO⁺) T cells. PD-L1 engagement on T cells resulted in reduced ERK phosphorylation and decreased AKT/mTOR/S6 signaling. Importantly, T cells from rheumatoid arthritis patients exhibited high basal levels of phosphorylated ERK and following PD-L1 cross-linking both ERK signaling and the AKT/mTOR/S6 pathway failed to be down modulated, making them refractory to the acquisition of a regulatory phenotype. Altogether, our results suggest that PD-L1 signaling on memory T cells could play an important role in resolving inflammatory responses; maintaining a tolerogenic environment and its failure could contribute to ongoing autoimmunity.

This study shows that programmed death cell receptor ligand 1 (PD-L1) signaling in memory CD4+ T cells from healthy individuals induces a regulatory phenotype; this mechanism seems to be defective in equivalent T cells from rheumatoid arthritis patients and could be in part responsible for the pathology.     

Protozoan feeding and bacterial wall growth.

Monod's model is often assumed to describe the kinetics of feeding of a protozoan population on a bacterial population in a chemostat. An earlier study (J. L. Jost et al., J. Bacteriol., 113, 84 (1973)) of the feeding of Tetrahymena pyriformis on either Escherichia coli or Azotobacter vinelandii found that this model correctly predicted the occurrence of sustained oscillations of population densities but made predictions of minimum bacterial population densities that were much smaller than those observed. The earlier study removed the discrepancy between the model and data by replacing Monod's model with a different model. It is shown in the present study that the discrepancy can be explained equally as well if Monod's model for the feed relation is retained and if, in addition, growth of bacteria on the chemostat walls is allowed for in the model equations.     

On the rate of genetic adaptation under natural selection.

Unsaturated fatty acids are constituents of nearly all biological membranes. They are always present in membranes which possess transmembrane potentials. Two completely different biosynthetic routes have evolved (aerobic and anaerobic) for placing cis double bonds in the 9 position on the fatty acids of membrane lipids. Bacterial membranes contain primarily monounsaturated fatty acids, whereas eukaryote membranes contain a significant fraction of polyunsaturated fatty acids. The polyunsaturated fatty acids are concentrated in organelles, such as chloroplasts and mitochondria that are known to manipulate transmembrane potentials. I propose that the function of the unsaturated fatty acids is to facilitate the transmission of a local compaction of the membrane (in response to a transmembrane potential) laterally through the membrane. The role of the cis double bond at position 9 is twofold: first to create a kink in the chains of a large fraction of membrane fatty acids enhancing the separation of two regions in the membrane and second to enhance the rigidity of the membrane in the region between the head group and the 9 double bond. This ordered region contains those carbons proximal to the 9 carbon and which are in a regular array of trans conformations. The presence of a reasonable proportion of cis double bonds at position 9 will tend to maintain these trans conformations utilizing pi-pi (van der Waals) interactions between adjacent hydrocarbon chains at position 9. The disordered region contains the carbons distal to the 9 carbon. These have greater degrees of freedom and considerable gauche conformations. The role of the double bonds in the polyunsaturated fatty acids distal to carbon 9 is to facilitate trans bilayer pi-pi (van der Waals) interactions enhancing compaction of the bilayer during the electrostriction. I further propose that it is the function of the ionic headgroups to form an interlocking polyionic network which constitutes an elastic sheet. These ionic interactions would serve as the restoring force converting the compaction into a wave. The facilitation of the compaction of the bilayer together with the polyionic restoring force permits the membrane to transmit conformational changes from one transmembrane protein to another. Since transmembrane potentials are created and responded to by proteins each in a single location, it is thus proposed that a potential compaction wave emanates from the first protein in all directions in the plane of the membrane. The proposed wave would have both physical and electrical components. The electrohydrodynamic wave would require that the compaction oscillations be coupled to an oscillating electrical field. These proposals are applied to mitochondrial oxidative phosphorylation, and to transport across biological membranes.     

Unfolding of beta‐lactoglobulin on the surface of polystyrene nanoparticles: Experimental and computational approaches

Structural changes ensuing from the non‐covalent absorption of bovine beta‐lactoglobulin (BLG) on the surface of polystyrene nanoparticles were investigated by using spectroscopic approaches, by assessing the reactivity of specific residues, and by limited proteolysis/mass spectrometry. Also, the immunoreactivity of absorbed and free BLG was compared. All these approaches indicated substantial rearrangements of the protein structure in the absorbed state, in spite of the reported structural rigidity of BLG. Changes made evident by experimental measurements were confirmed by computational approaches. These indicate that adsorption‐related changes are most marked in the area between the main C‐terminal alpha helix and the beta‐barrel, and lead to full exposure of the thiol on Cys₁₂₁, consistent with experimental measurements. In the computational model of bound BLG, both Trp₆₁ and Trp₁₉ also move away from their neighboring quenchers and become solvent‐exposed, as indicated by fluorescence measurement. Upon binding, the beta‐barrel also loosens, with a substantial increase in immunoreactivity and with noticeable changes in the trypsinolytic pattern. The possible general significance of the structural changes reported here for non‐covalently adsorbed BLG is discussed with respect to recognition events involving surface‐bound proteins, as are aspects related to the carrier function(s) of BLG, and to its use as a common ingredient in many food systems. Proteins 2014; 82:1272–1282. © 2013 Wiley Periodicals, Inc.     

Removal of ferritin-bound iron by DL-dihydrolipoate and DL-dihydrolipoamide

The naturally occurring dithiols DL-dihydrolipoate and DL-dihydrolipoamide were tested for their ability in the removal of ferritin-bound iron. Both compounds remove the iron stored inside the protein by complexing it in the ferric form. The iron can be reduced to the ferrous form by excess dithiol, but this is not necessary for complete removal. Reaction is complete in few hours and, at molar ratios of chelator to metal higher than 10, more than 60% of the ferritin-bound iron was removed. The amount of iron stored in the ferritin molecule does not affect the rate and the yield of the removal reaction. The iron-removing ability of DL-dihydrolipoate was found to be identical to that of an equimolar solution of sodium dithionite, and to be pH-dependent. Results are discussed in terms of the molecular architecture of ferritin and of the chelators, and their possible physiological relevance is pointed out.     

Identification of the genetic locus responsible for non-polar root induction by Agrobacterium rhizogenes 1855

Summary Root proliferation can be induced by Agrobacterium rhizogenes on carrot discs both on the apical and basal surface (facing the root apex and base, respectively) or on the apical surface only, depending on the bacterial strain. This differential response on the two surfaces is denominated polarity. We correlate the polarity of some strains with the absence of an Ri plasmid genetic locus, present in non polar strains such as A. rhizogenes 1855, which bears sequence homology with the auxin genes of Ti plasmid T-DNA. We demonstrate that this locus is responsible for root induction on the basal surface since insertion of a transposon in this region of pRi1855 induces polarity in this strain.     

Fingerprinting and sequence homology of plasmids from different virulent strains of Agrobacterium rhizogenes

Several wild-type virulent strains of Agrobacterium rhizogenes, belonging to both biotypes 1 and 2, were analyzed for plasmid content. All the strains were found to harbor at least one large plasmid, of a size comparable to that of A. tumefaciens Ti plasmids as determined by electron microscopy. The plasmids were characterized by restriction endonuclease finger-printing and compared for sequence homology by the Southern blot-hybridization technique. Despite the diversity of the restriction cleavage patterns, the plasmids of the various strains share rather extensive sequence homology. All of the biotype 1 organisms analyzed were shown to harbor one common plasmid.     

Identification of T-DNA in the root-inducing plasmid of the agropine type Agrobacterium rhizogenes 1855

The region of the virulence plasmid of the agropine type Agrobacterium rhizogenes 1855 (pRi-1855) which is transferred to plant cells upon infection (T-DNA) has been identified by means of Southern blot hybridizations with the T-DNA of the mannopine type A. rhizogenes 8196. The presence in the plant genome of the pRi-1855 sequences thus identified is demonstrated in carrot roots derived from infection with strain 1855. The T-DNA of pRi-1855 has been mapped by means of cloned Eco RI partial digests. Although strongly homologous with each other, the cores of the T-regions of the mannopine and agropine Ri plasmids are not colinear since the latter contains a central segment of DNA which is absent from the T-region of pRi-8196. Unexpected homologies between the T-region of pRi-1855 and normal carrot DNA have been observed and are discussed here.Abbreviations YMB yeast mannitol broth - LS Linsmaier and Skoog - BSA bovine serum albumin - SSC 0.15 M NaCl, 0.015 M Na-citrate - MD megadalton     

Protective effects of poly (ADP-ribose) synthase inhibitors in zymosan-activated plasma induced paw edema.

The aim of the present study was to investigate the role of poly (ADP-ribose) synthetase (PARS) in a model of acute local inflammation (zymosan-activated plasma (ZAP)-induced paw edema), in which the oxyradicals, nitric oxide and peroxynitrite, are known to play a crucial role. Injection of zymosan-activated plasma (ZAP) into the rat paw induced edema formation. The maximal increase in paw volume was observed at three hours after administration (maximal in paw volume: 1.29+/-0.09 ml). At this time point, there was a marked increase in neutrophil infiltration in the paw, as measured by an increase in myeloperoxidase (MPO) activity in the paw tissue (260+/-25 mU/100 mg wet tissue). However, ZAP-induced paw edema was significantly reduced in a dose-dependent manner by treatment with 3-aminobenzamide (3-AB) or nicotinamide (NIC), two inhibitors of PARS, at 1, 2, 3, 4 hours after ZAP injection. PARS inhibition also caused a significant reduction of MPO activity. The paw tissues were also examined immunohistochemically for the presence of nitrotyrosine (a footprint for peroxynitrite formation). At 3 h following ZAP injection, staining for nitrotyrosine were also found to be localised within discrete cells in the inflamed paw tissue. Treatment with PARS inhibitor prevented the appearance of nitrotyrosine in the tissues. Our results suggest that in paw edema induced by ZAP, inhibition of PARS exert potent anti-inflammatory effects.