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

Warrington et al. Allergy, Asthma & Clinical Immunology 2011 7(Suppl 1):S1   doi:10.1186/1710-1492-7-S1-S1