Marginal zone macrophages express a murine homologue of DC-SIGN that captures blood-borne antigens in vivo

Antigen-presenting cells are localized in essentially every tissue, where they operate at the interface of innate and acquired immunity by capturing pathogens and presenting pathogen-derived peptides to T cells. C-type lectins are important pathogen recognition receptors and the C-type lectin, dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN), is unique in that, in addition to pathogen capture, it regulates adhesion processes such as DC trafficking and T-cell synapse formation. We have isolated a murine homologue of DC-SIGN that is identical to the previously reported murine homologue mSIGNR1. mSIGNR1 is more closely related to the human DC-SIGN homologue L-SIGN than to DC-SIGN itself because mSIGNR1 is specifically expressed by liver sinusoidal endothelial cells, similar to L-SIGN, and not by DCs. Moreover, mSIGNR1 is also expressed by medullary and subcapsular macrophages in lymph nodes and by marginal zone macrophages (MZMs) in the spleen. Strikingly, these MZMs are in direct contact with the bloodstream and efficiently capture specific polysaccharide antigens present on the surface of encapsulated bacteria. We have investigated the in vivo function of mSIGNR1 on MZMs in spleen. We demonstrate here that mSIGNR1 functions in vivo as a pathogen recognition receptor on MZMs that capture blood-borne antigens, which are rapidly internalized and targeted to lysosomes for processing. Moreover, the antigen capture is completely blocked in vivo by the blocking mSIGNR1-specific antibodies. Thus, mSIGNR1, a murine homologue of DC-SIGN, is important in the defense against pathogens and this study will facilitate further investigations into the in vivo function of DC-SIGN and its homologues.     

Insulin-regulated aminopeptidase deficiency provides protection against ischemic stroke in mice

Recent studies have demonstrated that angiotensin IV (Ang IV) provides protection against brain injury caused by cerebral ischemia. Ang IV is a potent inhibitor of insulin-regulated aminopeptidase (IRAP). Therefore, we examined the effect of IRAP gene inactivation on neuroprotection following transient middle cerebral artery occlusion (MCAo) in mice. IRAP knockout mice and wild-type controls were subjected to 2?h of transient MCAo using the intraluminal filament technique. Twenty-four hours after reperfusion, neurological deficits of the stroke-induced mice were assessed and infarct volumes were measured by TTC staining. The cerebral infarct volume was significantly reduced in the IRAP knockout mice compared to wild-type littermates with corresponding improvement in neurological performance at 24?h post-ischemia. An increase in compensatory cerebral blood flow during MCAo was observed in the IRAP knockout animals with no differences in cerebral vascular anatomy detected. The current study demonstrates that deletion of the IRAP gene protects the brain from ischemic damage analogous to the effect of the IRAP inhibitor, Ang IV. This study indicates that IRAP is potentially a new therapeutic target for the development of treatment for ischemic stroke.     

Subcutaneous Dissemination from an Orbital Diffuse Large B Cell Lymphoma

Secondary cutaneous dissemination from an orbital diffuse large B cell lymphoma has not been described before. The authors report an unusual case of anaplastic variant of diffuse large B cell lymphoma which primarily presented in the orbit and during the course of disease had subcutaneous dissemination.     

Neutrophil dysfunction in a family with a SAPHO syndrome–like phenotype

SAPHO syndrome (synovitis, acne, pustulosis, hyperostosis, osteitis) is an inflammatory disorder of the bone, skin, and joints. We describe a family with multiple affected members who segregate a SAPHO syndrome–like phenotype, and we report the results of neutrophil studies and candidate gene analysis. We obtained written informed consent and a family history and reviewed medical records. We collected DNA and sequenced candidate genes, and we performed functional studies on neutrophils isolated from the proband and her mother. The pedigree segregated chronic osteomyelitis and cutaneous inflammation in a pattern that suggested an autosomal‐dominant disorder. No coding sequence mutations were detected in PSTPIP1, PSTPIP2, LPIN2, SH3BP2, or NCF4. Analysis of neutrophil function in the proband, including nitroblue tetrazolium tests, myeloperoxidase assays, neutrophil chemotaxis, and neutrophil chemotaxis assays, revealed no identifiable abnormalities. However, an abnormality in the luminol, but not the isoluminol, respiratory burst assays following stimulation with phorbol myristate acetate (PMA) was detected in neutrophils isolated from the affected proband. Internal oxidant production was also reduced in the proband and her mother when neutrophils were treated with fMLP with or without platelet‐activating factor, PMA alone, or tumor necrosis factor α alone. This family segregates a disorder characterized by chronic inflammation of the skin and bone. Functional differences in neutrophils exist between affected individuals and controls. The biologic significance of this defect remains unknown. Identification of the gene defect will help identify an immunologic pathway that, when dysregulated, causes inflammation of the skin and bone.