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 | |