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

Berardo De Jesus Rodriguez,Daniel Mollé,Isabelle Virlogeux-Payant,Claire Chevaleyre,Mustapha Berri,Henri Salmon,François Boulay,Joëlle Léonil,François Meurens,Gwénaële Henry

doi:10.1186/1471-2172-10-4

Abstract

BackgroundNormal 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.ResultsThe 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.ConclusionThese data are consistent with the SAA23–45 fragment being involved in preplasma B-cell recruitment to the mammary gland and resultant benefit to the neonate.

Highlights

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
Chemoattractant activity of whey ultrafiltrate Previous investigations have shown that the removal of fat and casein did not result in the loss of the original chemoattractant activity (CA) of skimmed milk
As CA was similar for lymphocytes from the mesenteric lymp node (MLN) and the ileal lymph node (ILN), we subsequently evaluated CA principally on B-cell lymphoblasts and MLN lymphocytes

Summary

Introduction

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. The mammary gland (MG) secretion is essential for the survival of neonatal mammals [1] This organ is a tertiary extralymphoid tissue with non-organised lymphoid components [1,2]. T lymphocytes accumulate in the MG during gestation whereas B cells and their plasma cell derivatives progressively accumulate during lactation [3,6,7,8]. Colostrum and milk immunoglobulins (Igs) are the net result of Ig extravasation from blood and local Ig production by plasma cells [9]. These plasma cells are derived from remote tissue precursors which are induced either in systemic and in mucosal sites, depending on Ig isotype. In single-stomached animals, IgA is secreted by IgA plasmablasts, which originate in the gut [6,8,10,11,12] whereas IgG is derived from systemic sites [13]

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