Innate Immunity

Overview

Innate immunity is the body's first-line, non-specific defense against pathogens — comprising physical barriers (epithelium, mucus), antimicrobial molecules (calprotectin, lactoferrin, defensins), pattern recognition receptors (TLRs, NOD-like receptors), and phagocytic cells (macrophages, neutrophils, dendritic cells). In the WikiBiome framework, innate immunity is inseparable from nutritional immunity — the host strategy of restricting essential metals from pathogens.

Metal-Mediated Innate Defense

The innate immune system deploys metals as weapons:

  • calprotectin: Released by neutrophils; sequesters zinc and manganese, starving pathogens of essential cofactors.
  • lactoferrin: Binds free iron at mucosal surfaces; denies iron to siderophore-dependent pathogens.
  • hepcidin: IL-6-induced master iron regulator; sequesters systemic iron during infection.
  • lipocalin 2: Neutralizes bacterial enterobactin (the strongest known siderophore).
  • Copper burst: Macrophages pump toxic copper into phagosomes to kill engulfed bacteria.
  • Zinc intoxication: Macrophages deliver lethal zinc doses to Salmonella-containing vacuoles.

Microbiome Shaping

The innate immune system shapes the microbiome, and the microbiome shapes innate immunity:

  • TLR signaling: Microbial LPS (TLR4), lipoteichoic acid (TLR2), flagellin (TLR5), and CpG DNA (TLR9) train innate immune responses [1].
  • Peptidoglycan recognition proteins (PGRPs): Kill bacteria via metal-mediated oxidative, thiol, and osmotic stress — a direct intersection of innate immunity and metal toxicity [2].
  • Intestinal immunity: Iron homeostasis in the gut directly modulates innate immune cell function [3].
  • Crohn's disease: Defective innate immunity (NOD2 mutations) leads to impaired bacterial clearance and chronic inflammation [4].

Cross-References

References (6)

  1. Chen S, Jiang D, Zhuang Q et al. (2024). Esophageal microbial dysbiosis impairs mucosal barrier integrity via toll-like receptor 2 pathway in patients with gastroesophageal reflux symptoms. Journal of Translational Medicine. doi:10.1186/s12967-024-05878-1
  2. Dipika R. Kashyap, Minhui Wang, Li-Hung Liu et al. (2014). Kashyap et al. 2014 — Peptidoglycan Recognition Proteins Kill Bacteria by Inducing Oxidative, Thiol, and Metal Stress. PLoS Pathogens. doi:10.1371/journal.ppat.1004280
  3. ★Honghong Bao, Yi Wang, Hanlin Xiong et al. (2024). Mechanism of Iron Ion Homeostasis in Intestinal Immunity and Gut Microbiota Remodeling. International Journal of Molecular Sciences
  4. Haag LM, Siegmund B (2015). Intestinal Microbiota and the Innate Immune System - a Crosstalk in Crohn's Disease Pathogenesis. Frontiers in Immunology. doi:10.3389/fimmu.2015.00489
  5. Natalia A. Borges, Amanda F. Barros, Lia S. Nakao et al. (2016). Protein-Bound Uremic Toxins from Gut Microbiota and Inflammatory Markers in CKD. Journal of Renal Nutrition. doi:10.1053/j.jrn.2016.07.005
  6. Chen, et al. (2026). Chen et al. 2026 — Metalloimmunology in the Tumor Microenvironment. Theranostics. doi:10.7150/thno.121988

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