Question

Explain the role of innate immunity in protection from infectious agents.

Answer 1

Innate immunity is non-specific, present at birth and always available. It protects the body from infectious agents through four types of barriers:

1. Physical (anatomical) barriers: The hard keratinised skin prevents entry of most bacteria and viruses; mucous membranes of the respiratory, gastrointestinal and urogenital tracts trap microbes, and cilia sweep them out by coughing or sneezing.
2. Physiological barriers: Fever inhibits the growth of germs and activates defence mechanisms; the acidic pH of the stomach (3–5) and of skin secretions kills swallowed bacteria; lysozymes in saliva, tears and perspiration destroy bacterial cell walls.
3. Cellular (phagocytic) barriers: Macrophages and neutrophils engulf and kill microbes by phagocytosis; natural killer cells kill virus-infected cells and cancer cells by releasing perforins that form pores in the target cell membrane.
4. Cytokine barriers: Virus-infected cells secrete interferons, glycoproteins which make neighbouring non-infected cells resistant to the virus.

Thus innate immunity acts as the first and second lines of defence, preventing the entry of pathogens and destroying those that manage to enter the body, thereby protecting the body from infectious agents.