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Intestinal macrophages: unique effector cells of the innate immune system

Authors

  • Phillip D. Smith,

    Corresponding author
    1. Department of Medicine (Gastroenterology and Hepatology), University of Alabama at Birmingham, and the Birmingham VA Medical Center, Birmingham, AL, USA.
      * Dr Phillip D. Smith
      Department of Medicine (Gastroenterology and Hepatology)
      University of Alabama at Birmingham
      703, 19th Street South
      Birmingham, AL 35294
      USA
      Tel.: +1 205 975 9254
      Fax: +1 205 934 8493
      E-mail: pdsmith@uab.edu
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  • Christina Ochsenbauer-Jambor,

    1. Department of Medicine (Gastroenterology and Hepatology), University of Alabama at Birmingham, and the Birmingham VA Medical Center, Birmingham, AL, USA.
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  • Lesley E. Smythies

    1. Department of Medicine (Gastroenterology and Hepatology), University of Alabama at Birmingham, and the Birmingham VA Medical Center, Birmingham, AL, USA.
    Search for more papers by this author

* Dr Phillip D. Smith
Department of Medicine (Gastroenterology and Hepatology)
University of Alabama at Birmingham
703, 19th Street South
Birmingham, AL 35294
USA
Tel.: +1 205 975 9254
Fax: +1 205 934 8493
E-mail: pdsmith@uab.edu

Abstract

Summary:  The gastrointestinal mucosa is the largest reservoir of macrophages in the body. These important effector cells are derived from blood monocytes that are recruited to the lamina propria by endogenous chemoattractants in the non-inflamed mucosa and by inflammatory chemokines and bacterial products during inflammation. In the non-inflamed mucosa, newly recruited pro-inflammatory monocytes are exposed to lamina propria stromal (extracellular matrix) factors that induce phenotypic and functional differentiation into non-inflammatory macrophages. As a consequence of this differentiation, resident lamina propria macrophages are strikingly downregulated for the expression of innate response receptors, such as the receptors for lipopolysaccharide, immunoglobulin G (IgG), and IgA, and the production of pro-inflammatory cytokines, including interleukin-1 (IL-1), IL-6, IL-8, and tumor necrosis factor-α. Despite downregulated pro-inflammatory function, strong phagocytic and bactericidal activities remain intact. Thus, in the non-inflamed intestinal mucosa, lamina propria macrophages are non-inflammatory but retain avid scavenger and host defense functions, a unique but ideal phenotype and functional profile for effector cells in close proximity to immunostimulatory microorganisms and products.

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