Enhanced Antibody Production in Clever-1/Stabilin-1-Deficient Mice

Clever-1, encoded by the Stab1 gene, is a scavenger and leukocyte trafficking receptor expressed by subsets of vascular and lymphatic endothelial cells and immunosuppressive macrophages. Monocyte Clever-1 also modulates T cell activation. However, nothing is known about the possible links between B cell function and Clever-1. Here, we found that Stab1 knockout mice (Stab1(-/-)) lacking the Clever-1 protein from all cells present with abnormally high antibody levels under resting conditions and show enhanced humoral immune responses after immunization with protein and carbohydrate antigens. Removal of the spleen does not abolish the augmented basal and post-immunization antibody levels in Clever-1-deficient mice. The increased IgG production is also present in mice in which Clever-1 is selectively ablated from macrophages. When compared to wildtype macrophages, Clever-1-deficient macrophages show increased TNF-alpha synthesis. In co-culture experiments, monocytes/macrophages deficient of Clever-1 support higher IgM production by B cells, which is blocked by TNF-alpha depletion. Collectively, our data show that the excessive inflammatory activity of monocytes/macrophages in the absence of Clever-1 results in augmented humoral immune responses in vivo

Fetal-derived macrophages dominate in adult mammary glands

Macrophages serve multiple functions including immune regulation, morphogenesis, tissue homeostasis and healing reactions. The current paradigm holds that mammary gland macrophages first arise postnatally during the prepubertal period from the bone marrow-derived monocytes. Here we delineate the origins of tissue-resident mammary gland macrophages using high-dimension phenotypic analyses, cell-fate mapping experiments, gene-deficient mice lacking selective macrophage subtypes, and antibody-based depletion strategies. We show that tissue-resident macrophages are found in mammary glands already before birth, and that the yolk sac-derived and fetal liver-derived macrophages outnumber the adult-derived macrophages in the mammary gland also in the adulthood. In addition, fetal-derived mammary gland macrophages have a characteristic phenotype, display preferential periductal and perivascular localization, and are highly active in scavenging. These findings identify fetal-derived macrophages as the predominant leukocyte type in the adult mammary gland stroma, and reveal previously unknown complexity of macrophage biology in the breast

Clever-1/Stabilin-1 regulates lymphocyte migration within lymphatics and leukocyte entrance to sites of inflammation

Clever-1/Stabilin-1 is a scavenger receptor present on lymphatic and sinusoidal endothelium as well as on a subset of type II macrophages. It is also induced on vasculature at sites of inflammation. However, its in vivo function has remained practically unknown and this work addresses those unknown aspects. We demonstrate using in vivo models that Clever-1/Stabilin-1 mediates migration of T and B lymphocytes to the draining lymph nodes in vivo and identify the adhesive epitope of the Clever-1/Stabilin-1 molecule responsible for the interaction between lymphocytes and lymphatic endothelium. Moreover, we demonstrate that Ab blocking of Clever-1/Stabilin-1 efficiently inhibits peritonitis in mice by decreasing the entrance of granulocytes by 50%, while migration of monocytes and lymphocytes into the inflamed peritoneum is prevented almost completely. Despite efficient anti-inflammatory activity the Ab therapy does not dramatically dampen immune responses against the bacterial and foreign protein Ag tested and bacterial clearance. These results indicate that anti-Clever-1/Stabilin-1 treatment can target two different arms of the vasculature - traffic via lymphatics and inflamed blood vessels.</p

Primary Amine Oxidase of Escherichia coli Is a Metabolic Enzyme that Can Use a Human Leukocyte Molecule as a Substrate

Escherichia coli amine oxidase (ECAO), encoded by the tynA gene, catalyzes the oxidative deamination of aromatic amines into aldehydes through a well-established mechanism, but its exact biological role is unknown. We investigated the role of ECAO by screening environmental and human isolates for tynA and characterizing a tynA-deletion strain using microarray analysis and biochemical studies. The presence of tynA did not correlate with pathogenicity. In tynA+ Escherichia coli strains, ECAO enabled bacterial growth in phenylethylamine, and the resultant H2O2 was released into the growth medium. Some aminoglycoside antibiotics inhibited the enzymatic activity of ECAO, which could affect the growth of tynA+ bacteria. Our results suggest that tynA is a reserve gene used under stringent environmental conditions in which ECAO may, due to its production of H2O2, provide a growth advantage over other bacteria that are unable to manage high levels of this oxidant. In addition, ECAO, which resembles the human homolog hAOC3, is able to process an unknown substrate on human leukocytes.</p

Gene-expression profiling of different arms of lymphatic vasculature identifies candidates for manipulation of cell traffic

Afferent lymphatic vessels bring antigens and diverse populations of leukocytes to draining lymph nodes, whereas efferent lymphatics allow only lymphocytes and antigens to leave the nodes. Despite the fundamental importance of afferent vs. efferent lymphatics in immune response and cancer spread, the molecular characteristics of these different arms of the lymphatic vasculature are largely unknown. The objective of this work was to explore molecular differences behind the distinct functions of afferent and efferent lymphatic vessels, and find possible molecules mediating lymphocyte traffic. We used laser-capture microdissection and cell sorting to isolate lymphatic endothelial cells (LECs) from the subcapsular sinus (SS, afferent) and lymphatic sinus (LS, efferent) for transcriptional analyses. The results reveal marked differences between afferent and efferent LECs and identify molecules on lymphatic vessels. Further characterizations of Siglec-1 (CD169) and macrophage scavenger receptor 1 (MSR1/CD204), show that they are discriminatively expressed on lymphatic endothelium of the SS but not on lymphatic vasculature of the LS. In contrast, endomucin (EMCN) is present on the LS endothelium and not on lymphatic endothelium of the SS. Moreover, both murine and human MSR1 on lymphatic endothelium of the SS bind lymphocytes and in in vivo studies MSR1 regulates entrance of lymphocytes from the SS to the lymph node parenchyma. In conclusion, this paper reports surprisingly distinct molecular profiles for afferent and efferent lymphatics and a function for MSR1. These results may open avenues to explore some of the now-identified molecules as targets to manipulate the function of lymphatic vessels

Primary Amine Oxidase of Escherichia coli Is a Metabolic Enzyme that Can Use a Human Leukocyte Molecule as a Substrate

Escherichia coli amine oxidase (ECAO), encoded by the tynA gene, catalyzes the oxidative deamination of aromatic amines into aldehydes through a well-established mechanism, but its exact biological role is unknown. We investigated the role of ECAO by screening environmental and human isolates for tynA and characterizing a tynA-deletion strain using microarray analysis and biochemical studies. The presence of tynA did not correlate with pathogenicity. In tynA+ Escherichia coli strains, ECAO enabled bacterial growth in phenylethylamine, and the resultant H2O2 was released into the growth medium. Some aminoglycoside antibiotics inhibited the enzymatic activity of ECAO, which could affect the growth of tynA+ bacteria. Our results suggest that tynA is a reserve gene used under stringent environmental conditions in which ECAO may, due to its production of H2O2, provide a growth advantage over other bacteria that are unable to manage high levels of this oxidant. In addition, ECAO, which resembles the human homolog hAOC3, is able to process an unknown substrate on human leukocytes

The Inhibitory Effect of Salmon Calcitonin on Tri-Iodothyronine Induction of Early Hypertrophy in Articular Cartilage

Salmon calcitonin has chondroprotective effect both in vitro and in vivo, and is therefore being tested as a candidate drug for cartilage degenerative diseases. Recent studies have indicated that different chondrocyte phenotypes may express the calcitonin receptor (CTR) differentially. We tested for the presence of the CTR in chondrocytes from tri-iodothyronin (T3)-induced bovine articular cartilage explants. Moreover, investigated the effects of human and salmon calcitonin on the explants.Early chondrocyte hypertrophy was induced in bovine articular cartilage explants by stimulation over four days with 20 ng/mL T3. The degree of hypertrophy was investigated by molecular markers of hypertrophy (ALP, IHH, COLX and MMP13), by biochemical markers of cartilage turnover (C2M, P2NP and AGNxII) and histology. The expression of the CTR was detected by qPCR and immunohistochemistry. T3-induced explants were treated with salmon or human calcitonin. Calcitonin down-stream signaling was measured by levels of cAMP, and by the molecular markers.Compared with untreated control explants, T3 induction increased expression of the hypertrophic markers (p<0.05), of cartilage turnover (p<0.05), and of CTR (p<0.01). Salmon, but not human, calcitonin induced cAMP release (p<0.001). Salmon calcitonin also inhibited expression of markers of hypertrophy and cartilage turnover (p<0.05).T3 induced early hypertrophy of chondrocytes, which showed an elevated expression of the CTR and was thus a target for salmon calcitonin. Molecular marker levels indicated salmon, but not human, calcitonin protected the cartilage from hypertrophy. These results confirm that salmon calcitonin is able to modulate the CTR and thus have chondroprotective effects

Identification of the calcitonin receptor in osteoarthritic chondrocytes

<p>Abstract</p> <p>Background</p> <p>Preclinical and clinical studies have shown that salmon calcitonin has cartilage protective effects in joint degenerative diseases, such as osteoarthritis (OA). However, the presence of the calcitonin receptor (CTR) in articular cartilage chondrocytes is yet to be identified. In this study, we sought to further investigate the expression of the CTR in naïve human OA articular chondrocytes to gain further confirmation of the existents of the CTR in articular cartilage.</p> <p>Methods</p> <p>Total RNA was purified from primary chondrocytes from articular cartilage biopsies from four OA patients undergoing total knee replacement. High quality cDNA was produced using a dedicated reverse transcription polymerase chain reaction (RT-PCR) protocol. From this a nested PCR assay amplifying the full coding region of the CTR mRNA was completed. Western blotting and immunohistochemistry were used to characterize CTR protein on protein level in chondrocytes.</p> <p>Results</p> <p>The full coding transcript of the CTR isoform 2 was identified in all four individuals. DNA sequencing revealed a number of allelic variants of the gene including two potentially novel polymorphisms: a frame shift mutation, +473del, producing a shorter form of the receptor protein, and a single nucleotide polymorphism in the 3' non coding region of the transcript, +1443 C>T. A 53 kDa protein band, consistent with non-glycosylated CTR isoform 2, was detected in chondrocytes with a similar size to that expressed in osteoclasts. Moreover the CTR was identified in the plasma membrane and the chondrocyte lacuna of both primary chondrocytes and OA cartilage section.</p> <p>Conclusions</p> <p>Human OA articular cartilage chondrocytes do indeed express the CTR, which makes the articular a pharmacological target of salmon calcitonin. In addition, the results support previous findings suggesting that calcitonin has a direct anabolic effect on articular cartilage.</p