Fibrochondrogenesis results from mutations in the COL11A1 type XI collagen gene

Fibrochondrogenesis is a severe, autosomal-recessive, short-limbed skeletal dysplasia. In a single case of fibrochondrogenesis, whole-genome SNP genotyping identified unknown ancestral consanguinity by detecting three autozygous regions. Because of the predominantly skeletal nature of the phenotype, the 389 genes localized to the autozygous intervals were prioritized for mutation analysis by correlation of their expression with known cartilage-selective genes via the UCLA Gene Expression Tool, UGET. The gene encoding the α1 chain of type XI collagen (COL11A1) was the only cartilage-selective gene among the three candidate intervals. Sequence analysis of COL11A1 in two genetically independent fibrochondrogenesis cases demonstrated that each was a compound heterozygote for a loss-of-function mutation on one allele and a mutation predicting substitution for a conserved triple-helical glycine residue on the other. The parents who were carriers of missense mutations had myopia. Early-onset hearing loss was noted in both parents who carried a loss-of-function allele, suggesting COL11A1 as a locus for mild, dominantly inherited hearing loss. These findings identify COL11A1 as a locus for fibrochondrogenesis and indicate that there might be phenotypic manifestations among carriers.     

Pathogen-specific CD8 T cell responses are directly inhibited by IL-10

Regulation of CD8 T cell expansion and contraction is essential for successful immune defense against intracellular pathogens. IL-10 is a regulatory cytokine that can restrict T cell responses by inhibiting APC functions. IL-10, however, can also have direct effects on T cells. Although blockade or genetic deletion of IL-10 enhances T cell-mediated resistance to infections, the extent to which IL-10 limits in vivo APC function or T cell activation/proliferation remains unknown. Herein, we demonstrate that primary and memory CD8 T cell responses following Listeria monocytogenes infection are enhanced by the absence of IL-10. Surface expression of the IL-10R is transiently up-regulated on CD8 T cells following activation, suggesting that activated T cells can respond to IL-10 directly. Consistent with this notion, CD8 T cells lacking IL-10R2 underwent greater expansion than wild-type T cells upon L. monocytogenes infection. The absence of IL-10R2 on APCs, in contrast, did not enhance T cell responses following infection. Our studies demonstrate that IL-10 produced during bacterial infection directly limits expansion of pathogen-specific CD8 T cells and reveal an extrinsic regulatory mechanism that modulates the magnitude of memory T cell responses.     

The related adaptors, adaptor in lymphocytes of unknown function X and Rlk/Itk-binding protein, have nonredundant functions in lymphocytes

Adaptors play a critical role in regulating signaling pathways that control lymphocyte development and activation. Adaptor in lymphocytes of unknown function X (ALX) and Rlk/Itk-binding protein (RIBP) are adaptors related by structure and sequence, coexpressed in T cells. Mice deficient for each adaptor demonstrated that ALX and RIBP, respectively, negatively and positively regulate T cell activation in response to TCR/CD28 stimulation. However, these results did not preclude that they may function redundantly in other cell populations, or in response to other stimuli. Therefore, to understand the relationship between these related adaptors, ALX/RIBP-deficient mice were generated. We demonstrate that although ALX and RIBP are expressed throughout T cell development, T cell development occurs normally in these mice. Using the H-Y TCR transgenic model, positive and negative selection were found to proceed unimpeded in the absence of ALX and RIBP. We demonstrate that RIBP is also expressed in B cells; however, RIBP- and ALX/RIBP-deficient mice had normal B cell development, and responded equivalently to wild type in response to IgM, CD40, B cell-activating factor/B lymphocyte stimulator, CpG, and LPS. Interestingly, T cells deficient in both ALX and RIBP behaved similarly to those deficient in ALX alone during T cell activation in response to TCR/CD28, exhibiting increased IL-2 production, CD25 expression, and proliferation, thus showing that ALX deficiency masked the effect of RIBP deficiency. ALX/RIBP-deficient T cells did not have any alterations in either activation-induced cell death or Th1/2 polarization. Therefore, we did not find any functional redundancy or synergy during lymphocyte development, selection, activation, or survival in ALX/RIBP-deficient mice, demonstrating that these molecules function independently.     

Complement dependent amplification of the innate response to a cognate microbial ligand by the long pentraxin PTX3

The long pentraxin PTX3 is a fluid-phase pattern recognition receptor, which plays a nonredundant role in resistance against selected pathogens. PTX3 has properties similar to Abs; its production is induced by pathogen recognition, it recognizes microbial moieties, activates complement, and facilitates cellular recognition by phagocytes. The mechanisms responsible for the effector function of PTX3 in vivo have not been elucidated. OmpA, a major outer membrane protein of Gram-negative Enterobacteriaceae, is a microbial moiety recognized by PTX3. In the air pouch model, KpOmpA induces an inflammatory response, which is amplified by coadministration of PTX3 in terms of leukocyte recruitment and proinflammatory cytokine production. PTX3 did not affect the inflammatory response to LPS, a microbial moiety not recognized by PTX3. As PTX3 binds to C1q and modulates the activation of the complement cascade, we assessed the involvement of complement in the amplification of the response elicited by KpOmpA and PTX3. Experiments performed using cobra venom factor, C1-esterase inhibitor, and soluble complement receptor 1 indicate that PTX3 amplifies the inflammatory response to KpOmpA through complement activation. The results reported here demonstrate that PTX3 activates a complement-dependent humoral amplification loop of the innate response to a microbial ligand.     

Evolution of Hyperactive,Repetitive Antifreeze Proteins in Beetles

Some organisms that experience subzero temperatures, such as insects, fish, bacteria, and plants, synthesize antifreeze proteins (AFPs) that adsorb to surfaces of nascent ice crystals and inhibit their growth. Although some AFPs are globular and nonrepetitive, the majority are repetitive in both sequence and structure. In addition, they are frequently encoded by tandemly arrayed, multigene families. AFP isoforms from the mealworm beetle, Tenebrio molitor, are extremely potent and inhibit ice growth at temperatures below −5°C. They contain a 12-amino acid repeat with the sequence TCTxSxxCxxAx, each of which makes up one coil of the β-helix structure. TxT motifs are arrayed to form the ice-binding surface in all three known insect AFPs: the homologous AFPs from the two beetles, T. molitor and Dendroides canadensis, and the nonhomologous AFP from the spruce budworm, Choristoneura fumiferana. In this study, we have obtained the cDNA and genomic sequences of additional T. molitor isoforms. They show variation in the number of repeats (from 6 to 10) which can largely be explained by recombination at various TCT motifs. In addition, phylogenetic comparison of the AFPs from the two beetles suggests that gene loss and amplification may have occurred after the divergence of these species. In contrast to a previous study suggesting that T. molitor genes have undergone positive Darwinian selection (selection for heterogeneity), we propose that the higher than expected ratio of nonsynonymous-to-synonymous substitutions might result from selection for higher AT content in the third codon position. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. [Reviewing Editor: Dr. John Oakeshott]     

Insulin resistance and impaired baroreflex gain during pregnancy

Pregnancy decreases baroreflex gain, but the underlying mechanism is unclear. Insulin resistance, which has been associated with reduced transport of insulin into the brain, is a consistent feature of many conditions exhibiting impaired baroreflex gain, including pregnancy. Therefore, using conscious pregnant and nonpregnant rabbits, we tested the novel hypothesis that the pregnancy-induced impairment in baroreflex gain is due to insulin resistance and reduced brain insulin. Baroreflex gain was determined by quantifying changes in heart rate in response to stepwise steady-state changes in arterial pressure, secondary to infusion of nitroprusside and phenylephrine. We found that insulin sensitivity and baroreflex gain were strongly correlated in nonpregnant and term pregnant rabbits (r2 = 0.59). The decrease in insulin sensitivity and in baroreflex gain exhibited similar time courses throughout pregnancy, reaching significantly lower levels at 3 wk of gestation and remaining reduced at 4 wk (term is 31 days). Treatment of rabbits with the insulin-sensitizing drug rosiglitazone during pregnancy almost completely normalized baroreflex gain. Finally, pregnancy significantly lowered cerebrospinal fluid insulin concentrations. These data identify insulin resistance as a mechanism underlying pregnancy-induced baroreflex impairment and suggest, for the first time in any condition, that decreased brain insulin concentrations may be the link between reductions in peripheral insulin sensitivity and baroreflex gain.