Defective Expression and Function of the Leukocyte Associated Ig-like Receptor 1 in B Lymphocytes from Systemic Lupus Erythematosus Patients

Systemic lupus erythematosus (SLE) is characterized by the production of a wide array of autoantibodies and dysregulation of B cell function. The leukocyte associated Immunoglobulin (Ig)-like receptor (LAIR)1 is a transmembrane molecule belonging to Ig superfamily which binds to different types of collagen. Herein, we have determined the expression and function of LAIR1 on B lymphocyte from SLE patients. LAIR1 expression in peripheral blood B lymphocytes from 54 SLE, 24 mixed connective tissue disease (MCTD), 20 systemic sclerosis (SSc) patients, 14 rheumatoid arthritis (RA) and 40 sex and age matched healthy donors (HD) have been analyzed by immunofluorescence. The effect of LAIR1 ligation by specific monoclonal antibodies, collagen or collagen producing mesenchymal stromal cells from reactive lymph nodes or bone marrow on Ig production by pokeweed mitogen and B cell receptor (BCR)-mediated NF-kB activation was assessed by ELISA and TransAM assay. The percentage of CD20+ B lymphocytes lacking or showing reduced expression of LAIR1 was markedly increased in SLE and MCTD but not in SSc or RA patients compared to HD. The downregulation of LAIR1 expression was not dependent on corticosteroid therapy. Interestingly, LAIR1 engagement by collagen or collagen-producing mesenchymal stromal cells in SLE patients with low LAIR1 expression on B cells delivered a lower inhibiting signal on Ig production. In addition, NF-kB p65 subunit activation upon BCR and LAIR1 co-engagement was less inhibited in SLE patients than in HD. Our findings indicate defective LAIR1 expression and function in SLE B lymphocytes, possible contributing to an altered control of B lymphocytes behavior

A Novel Soluble Immune-Type Receptor (SITR) in Teleost Fish: Carp SITR Is Involved in the Nitric Oxide-Mediated Response to a Protozoan Parasite

Background- The innate immune system relies upon a wide range of germ-line encoded receptors including a large number of immunoglobulin superfamily (IgSF) receptors. Different Ig-like immune receptor families have been reported in mammals, birds, amphibians and fish. Most innate immune receptors of the IgSF are type I transmembrane proteins containing one or more extracellular Ig-like domains and their regulation of effector functions is mediated intracellularly by distinct stimulatory or inhibitory pathways. Methodology/Principal Findings - Carp SITR was found in a substracted cDNA repertoire from carp macrophages, enriched for genes up-regulated in response to the protozoan parasite Trypanoplasma borreli. Carp SITR is a type I protein with two extracellular Ig domains in a unique organisation of a N-proximal V/C2 (or I-) type and a C-proximal V-type Ig domain, devoid of a transmembrane domain or any intracytoplasmic signalling motif. The carp SITR C-proximal V-type Ig domain, in particular, has a close sequence similarity and conserved structural characteristics to the mammalian CD300 molecules. By generating an anti-SITR antibody we could show that SITR protein expression was restricted to cells of the myeloid lineage. Carp SITR is abundantly expressed in macrophages and is secreted upon in vitro stimulation with the protozoan parasite T. borreli. Secretion of SITR protein during in vivo T. borreli infection suggests a role for this IgSF receptor in the host response to this protozoan parasite. Overexpression of carp SITR in mouse macrophages and knock-down of SITR protein expression in carp macrophages, using morpholino antisense technology, provided evidence for the involvement of carp SITR in the parasite-induced NO production. Conclusion/Significance - We report the structural and functional characterization of a novel soluble immune-type receptor (SITR) in a teleost fish and propose a role for carp SITR in the NO-mediated response to a protozoan parasite

Inactivation of Staphylococcal Phenol Soluble Modulins by Serum Lipoprotein Particles

Staphylococcus aureus virulence has been associated with the production of phenol soluble modulins (PSM). PSM are known to activate, attract and lyse neutrophils. However, the functional characterizations were generally performed in the absence of human serum. Here, we demonstrate that human serum can inhibit all the previously-described activities of PSM. We observed that serum can fully block both the cell lysis and FPR2 activation of neutrophils. We show a direct interaction between PSM and serum lipoproteins in human serum and whole blood. Subsequent analysis using purified high, low, and very low density lipoproteins (HDL, LDL, and VLDL) revealed that they indeed neutralize PSM. The lipoprotein HDL showed highest binding and antagonizing capacity for PSM. Furthermore, we show potential intracellular production of PSM by S. aureus upon phagocytosis by neutrophils, which opens a new area for exploration of the intracellular lytic capacity of PSM. Collectively, our data show that in a serum environment the function of PSM as important extracellular toxins should be reconsidered