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Table 1 Summary of non-specific host-defense mechanisms for barriers of innate immunity [1].

From: An introduction to immunology and immunopathology





• Mechanical barrier retards entry of microbes

• Acidic environment (pH 3-5) retards growth of microbes

Mucous membrane

• Normal flora compete with microbes for attachment sites

• Mucous entraps foreign microbes

• Cilia propel microbes out of body



• Body temperature/fever response inhibits growth of some pathogens

Low pH

• Acidic pH of stomach kills most undigested microbes

Chemical mediators

• Lysozyme cleaves bacterial cell wall

• Interferon induces antiviral defenses in uninfected cells

• Complement lyses microbes or facilitates phagocytosis

Phagocytic/endocytic barriers


• Various cells internalize (endocytosis) and break down foreign macromolecules

• Specialized cells (blood monocytes, neutrophils, tissue macrophages) internalize (phagocytose), kill and digest whole organisms

Inflammatory barriers


• Tissue damage and infection induce leakage of vascular fluid containing serum protein with antibacterial activity, leading to influx of phagocytic cells into the affected area