Cellular and humoral immune response to recombinant Escherichia coli OmpA in cows.

Pascal Rainard,Maryline Répérant-Ferter,Florence B Gilbert,Pierre Germon,Christophe Gitton

doi:10.1371/journal.pone.0187369

Pascal Rainard, Maryline Répérant-Ferter + Show 3 more

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https://doi.org/10.1371/journal.pone.0187369

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Abstract

The outer membrane protein (Omp) A is a major constituent of the outer membrane of Escherichia coli. This protein has been used in several vaccine development studies, but seldom with a view to vaccinating against mastitis. The objective of this study was to investigate the immunogenicity of E. coli OmpA and its vaccine potential for cows. Both the humoral and cellular immune responses were investigated. The gene for OmpA of the mastitis-causing strain P4 was cloned and expressed, and the recombinant protein (rEcOmpA) purified. Cows were immunized twice with rEcOmpA with adjuvant one month apart by the systemic route. Before immunization, few antibodies to rEcOmpA were detected, and there was little production of IL-17A in a whole blood stimulation assay (WBA) with rEcOmpA. Antibodies to rEcOmpA were induced by immunization. These antibodies were not able to react with E. coli P4, but reacted with a rough P4 mutant prepared by inactivating the rfb locus. This suggests that the complete LPS O-chain precluded the accessibility of antibodies to their target at the outer membrane. The cellular immune response appeared to be biased towards a Th17-type, as more IL-17A than IFN-γ was produced in the OmpA-specific WBA. There was a good correlation between antibody titers and the production of IL-17A in the WBA. The intramammary instillation of rEcOmpA elicited a slight local inflammatory response which was not related to the WBA. Overall, the interest of OmpA as vaccine immunogen was not established, although other experimental conditions (dose, adjuvant, route) need to be investigated to conclude definitively. The study pointed to several important issues such as the accessibility of OmpA to antibodies and the weakness of Th1-type response induced by OmpA.

Highlights

The outer membrane protein A (OmpA) of Escherichia coli is an abundant integral protein of the outer membrane, which occurs at about 100,000 copies per cell [1]
Stimulation of HEK-TLR4 cells with recombinant E. coli OmpA (rEcOmpA) at 100 μg/mL led to secretion of CXCL8 to a level in between those obtained upon stimulation with uLPS at 10 ng/mL and 1 ng/mL
In this study we aimed at evaluating the immunogenicity of OmpA through the capacity of rEcOmpA to elicit antibodies and cell-mediated immune responses in the cow

Summary

Introduction

The outer membrane protein A (OmpA) of Escherichia coli is an abundant integral protein of the outer membrane, which occurs at about 100,000 copies per cell [1]. Immune response to OmpA killing of OmpA-positive E. coli [3] For these reasons and because it belongs to a class of bacterial proteins highly conserved among the Enterobacteriaceae family, OmpA has been considered as a potential antigen in vaccine research [4, 5]. The protein OmpA was considered as a target for host adaptive immune responses, those directed to the loops of the molecule exposed at the surface of the outer membrane [6]. As the early recruitment of neutrophils into the mammary gland constitutes a major defense against infection [9], and because the antigen-specific and innate immune responses cooperate to amplify milk leukocytosis [10], this cell-mediated immune response can be considered as a useful feature for a potential vaccine antigen. Because porins of certain Gram negative bacteria exert a polarizing immunomodulatory effect [13], we paid attention to the Th1/Th17 balance of the immune response to rEcOmpA

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