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Microbiology: An Evolving Science 4th Edition

Microbiology: An Evolving Science (4th Edition)

Book Edition4th Edition
PublisherW. W. Norton

Chapter 23, End of Chapter, Review Questions, Exercise 5

Page 938

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Innate immunity can be differentiated based on the various types of barriers to microbial infections.


The innate immune system is that which is present since birth and acts as the first line of defense that a host possesses. It is a nonspecific response against the foreign invader. It requires many effector mechanisms to function.


This type of immunity can be divided into different types based on the type of barriers:

  1. Physical barriers: It prevents the microbe entry from the outside environment into our body. The interfaces include the gastrointestinal tract, skin, lungs, genitourinary tract, and oral cavity. The skin is the main protective shield. It contains Langerhans cells (dendritic cells). Additionally, the mucosal membranes of gastrointestinal, respiratory and genitourinary tracts help trap the foreign particles. 
  2. Physiological and chemical barriers: The microbial growth is prevented by the body because of factors like hydrochloric acid in the stomach, saliva in the mouth, and the lysozymes present in our tears. Defensins are a set of cationic antimicrobial peptides produced by the host immune cells that destroy the cytoplasmic membrane of the microbes.
  3. Cellular barriers: There are different cells of the immune system that participate in the elimination of the disease causing microbe. They are polymorphonuclear leukocytes (eosinophils, neutrophils, and basophils), monocytes and lymphocytes in the blood. Also, the macrophages in the tissues. They destroy the pathogens either by phagocytosis or by releasing toxic chemicals.
  4. Cytokine barriers: The interferons (low molecular mass cytokines) are produced by the virus-infected or cancerous cells. They are released to prevent the further spread of infection to other normal host cells.

Verified Answer

Depending upon the barriers that provide defense against microbial infections, there are several barriers that provide innate immunity. These include:

  1. Physical barriers
  2. Chemical and physiological barriers
  3. Cellular barriers
  4. Cytokine barriers
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