SUMMARY Tissue effector cells of the monocyte lineage can differentiate into different cell types with specific cell function depending on their environment. The phenotype, developmental requirements, and functional mechanisms of immune protective macrophages that mediate the induction of transplantation tolerance remain elusive. Here, we demonstrate that costimulatory blockade favored accumulation of DC-SIGN-expressing macrophages that inhibited CD8+ T cell immunity and promoted CD4+Foxp3+ Treg cell expansion in numbers. Mechanistically, that simultaneous DC-SIGN engagement by fucosylated ligands and TLR4 signaling was required for production of immunoregulatory IL-10 associated with prolonged allograft survival. Deletion of DC-SIGN-expressing macrophages in vivo, interfering with their CSF1-dependent development, or preventing the DC-SIGN signaling pathway abrogated tolerance. Together, the results provide new insights into the tolerogenic effects of costimulatory blockade and identify DC-SIGN+ suppressive macrophages as crucial mediators of immunological tolerance with the concomitant therapeutic implications in the clinic.

Exposure of several human populations to arsenic has been associated with a high incidence of detrimental dermatological and carcinogenic effects. To date, studies examining the immunotoxic effects of arsenic in humans, and specifically in children, are lacking. Therefore, we evaluated several parameters of immunological status in a group of children exposed to arsenic through their drinking water. Peripheral blood mononuclear cells (PBMCs) of 90 children (6 to 10 years old) were collected. Proportions of lymphocyte subpopulations, PBMC mitogenic proliferative response, and urinary arsenic levels were evaluated. Increased urine arsenic levels were associated with a reduced proliferative response to phytohemaglutinin (PHA) stimulation (P=0.005), CD4 subpopulation proportion (P=0.092), CD4/CD8 ratio (P=0.056), and IL-2 secretion levels (P=0.003). Increased arsenic exposure was also associated with an increase in GM-CSF secretion by mononucleated cells (P=0.000). We did not observe changes in CD8, B, or NK cell proportions, nor did we observe changes in the secretion of IL-4, IL-10, or IFN-gamma by PHA-activated PBMCs. These data indicate that arsenic exposure could alter the activation processes of T cells, such that an immunosuppression status that favors opportunistic infections and carcinogenesis is produced together with increased GM-CSF secretion that may be associated with chronic inflammation.

Precipitation of Saccharomyces cerevisiae ribosomes by ethanol under experimental conditions that do not release the ribosomal proteins can affect the activity of the particles. In the presence of 0.4 M NH4Cl and 50% ethanol only the most acidic proteins from yeast and rat liver ribosomes are released. At 1 M NH4Cl two more non-acidic proteins are lost from the ribosomes. The release of the acidic proteins causes a small inactivation of the polymerizing activity of the particles, additional to that caused by the precipitation itself. The elongation-factor-2-dependent GTP hydrolysis of the ribosomes is, however, more affected by the loss of acidic proteins. These proteins can stimulate the GTPase but not the polymerising activity when added back to the treated particles. Eukaryotic proteins cannot be sustituted for bacterial acidic proteins L7 and L12. We have not detected immunological cross-reaction between acidic proteins from Escherichia coli and those from yeast, Artemia salina and rat liver or between acidic proteins from these eukaryotic ribosomes among themselves.The existence in eukaryotic ribosomes of acidic proteins with electrophoretic mobility and molecular weight similar to that of proteins L7 and L12 from Escherichia coli ribosomes has been reported [l-41. In some cases antibodies against the bacterial proteins were reported to cross-react with the eukaryotic proteins [I].Functional similarities between acidic proteins from bacterial and higher cells have been reported [2,6] using particles deprived of these proteins by washing the ribosomes with 1 M NH4Cl and 50% ethanol as described for E. coli [7]. It was later found that this treatment induces the release of two proteins in addition to the acidic ones [3]. Therefore, the conclusions drawn from this type of experiment must be re-examined.We have found experimental conditions that permit the selective release of most acidic proteins from rat liver and yeast ribosomes. The roles of the acidic proteins in both types of ribosomes have been investigated using these particles. The results presented in this report indicate differences in the requirements of acidic proteins for the function of eukaryotic and prokaryotic ribosomes.Ahhreviatiun. EF-1, 2, etc, elongation factors 1, 2, etc MATERIALS AND METHODS Preparation of RibosomesSaccharornyces cerevisiae, strain Y 166 was grown in yeast extract/peptone/glucose medium [S] in a LabLine/S.M.S. Hi-density fermentor, up, to late exponential phase. Cells were broken by sea-sand grinding and the ribosomes were washed in high-salt buffers [9] and finally resuspended in 80 mM KCI, 10 mM MgCL and 20 mM Tris-HCI, pH 7.4 (buffer 1). The particles were stored in liquid nitrogen. Rat liver ribosomes were prepared as described elsewhere [lo]. Preparation of Core Particles and Split Protein FractionsThe ribosomes were dissolved at 4 mg/ml in 10 mM imidazol-HC1 buffer pH 7.4, containing 20 mM MgC12, 1 mM 2-mercaptoethanol and either 0.4 M or 1 M NH4Cl. Ethanol was added up to 50% (v/v) final concentration in two steps...