Table 1 Summary of non-specific host-defense mechanisms for barriers of innate immunity [1]
Barrier | Mechanism |
|---|---|
Anatomic | |
 Skin | • 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 |
Physiologic | |
 Temperature | • 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 |