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      Identification in milk of a serum amyloid A peptide chemoattractant for B lymphoblasts

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          Abstract

          Background

          Normal mammary gland contains an extravascular population of B lymphoblasts, precursors of the immunoglobulin plasma cells that play a key role in the passive protection of neonates by secreting immunoglobulins to colostrum and milk. We investigated the presence of chemoattractants in the milk by analysing the chemoattractant activity of various fractions of this secretion. Milk chemoattractants are potentially involved in the recruitment of lymphocytes from the maternal bloodstream in lactating mammary glands.

          Results

          The dilution-related lymphoid cell chemoattraction of whey was associated with a < 10 kDa ultrafiltrate. Active fractions were purified by reverse-phase high performance liquid chromatography. Two peptides of 2.7 kDa (DMREANYKNSDKYFHARGNYDAA) and 1 kDa (RPPGLPDKY) were identified as fragments of the SAA protein family, tentatively identified as SAA2. Only the 2.7 kDa synthetic peptide displayed chemotactic activity, at two different optimal concentrations. At the lower concentration (3.7 nM), it attracted B-cell lymphoblasts, whereas at the higher (3.7 μM), it attracted B lymphocytes. Then, the SAA mRNA expression was analysed and we observed more SAA transcripts during lactation than gestation.

          Conclusion

          These data are consistent with the SAA 23–45 fragment being involved in preplasma B-cell recruitment to the mammary gland and resultant benefit to the neonate.

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          Most cited references58

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          Formyl-peptide receptors revisited.

          Leukocytes accumulate at sites of inflammation and microbial infection in direct response to locally produced chemotactic factors, which signal through specific G protein-coupled receptors. The first chemotactic factors to be structurally defined were the N-formyl peptides. Unlike other leukocyte chemoattractants, N-formyl peptides could originate from either an endogenous source, such as the mitochondrial proteins of ruptured host cells, or an exogenous source, such as the proteins of invading pathogens. This suggests that the formyl-peptide receptor (FPR) and its variant FPRL1 (FPR-like 1) are involved in host defense against bacterial infection and in the clearance of damaged cells. Recently, additional, more complex, roles for these receptors have been proposed because FPR, and to a greater extent FPRL1, have been found to interact with a menagerie of structurally diverse pro- and anti-inflammatory ligands associated with different diseases, including amyloidosis, Alzheimer's disease, prion disease and HIV. How these receptors recognize such diverse ligands, which are the most important in vivo, and how they contribute to disease pathogenesis and host defense are basic questions currently under investigation that could lead to new therapeutic targets.
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            New perspectives in cell adhesion: RGD and integrins.

            Rapid progress has been made in the understanding of the molecular interactions that result in cell adhesion. Many adhesive proteins present in extracellular matrices and in the blood contain the tripeptide arginine-glycine-aspartic acid (RGD) as their cell recognition site. These proteins include fibronectin, vitronectin, osteopontin, collagens, thrombospondin, fibrinogen, and von Willebrand factor. The RGD sequences of each of the adhesive proteins are recognized by at least one member of a family of structurally related receptors, integrins, which are heterodimeric proteins with two membrane-spanning subunits. Some of these receptors bind to the RGD sequence of a single adhesion protein only, whereas others recognize groups of them. The conformation of the RGD sequence in the individual proteins may be critical to this recognition specificity. On the cytoplasmic side of the plasma membrane, the receptors connect the extracellular matrix to the cytoskeleton. More than ten proved or suspected RGD-containing adhesion-promoting proteins have already been identified, and the integrin family includes at least as many receptors recognizing these proteins. Together, the adhesion proteins and their receptors constitute a versatile recognition system providing cells with anchorage, traction for migration, and signals for polarity, position, differentiation, and possibly growth.
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              Origin of IgA-secreting plasma cells in the mammary gland

              Lymphoblasts from the mesenteric lymph nodes (MN) of mice home to the mammary glands of syngeneic recipients late in pregnancy and during lactation, and within hours of transfer most can be shown to contain IgA. Homing does not occur in virgins, in early pregnancy, or after weaning. Homing MN lymphoblasts are sensitive to antiserum to IgA plus complement, but not to other class-specific antisera. Thus, lymphoblasts in MN with the potential to home to the mammary gland are already committed to IgA synthesis and bear surface IgA before reaching their destination. These results explain observations, made by others, of specific IgA antibodies and IgA plasma cells in milk and colostrum after oral immunization. Under natural conditions it is likely that IgA precursor cells, after stimulation in the gut-associated lymphoid tissue by intestinal antigens, migrate to the mammary gland where they secrete antibodies which constitute an important defense mechanism of the newborn. In the absence of lactation, these cells probably form part of the normal traffic to the lamina propria of the small intestine.
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                Author and article information

                Journal
                BMC Immunol
                BMC Immunology
                BioMed Central
                1471-2172
                2009
                23 January 2009
                : 10
                : 4
                Affiliations
                [1 ]Institut National de la Recherche Agronomique (INRA), UR1282, Infectiologie Animale et Santé Publique, F-37380, Nouzilly (Tours), France
                [2 ]UMR Science et Technologie du Lait et de l'Oeuf, INRA-Agrocampus 1253, 65 rue de Saint-Brieuc, 35042 Rennes CEDEX, France
                [3 ]Laboratorio de Patologia Animal, Universidad de Antioquia, Medellin, Colombia
                [4 ]Commissariat à l'Energie Atomique (CEA), DSV, iRTSV, Laboratoire Biochimie et Biophysique des Systèmes Intégrés, Grenoble, F-38054, France. CNRS, UMR 5092, 17 rue des Martyrs, Grenoble F-38054, France. Université Joseph Fourier, Grenoble, F-38000, France
                Article
                1471-2172-10-4
                10.1186/1471-2172-10-4
                2637234
                19166592
                fa62a45b-ee3f-4aa2-9c9c-c2697bde9202
                Copyright © 2009 Rodriguez et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 17 September 2008
                : 23 January 2009
                Categories
                Research Article

                Immunology
                Immunology

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