An introduction to immunology and immunopathology

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