recap

41.1 recap

All animals have innate defenses against pathogens, and vertebrates have innate and adaptive defenses. Both kinds of mechanisms are based on the ability to differentiate self from nonself. Innate defenses target a broad range of molecules and organisms, whereas adaptive defenses target specific pathogens. Both innate and adaptive defenses involve specialized white blood cells.

learning outcomes

You should be able to:

  • Compare various types of defense mechanisms.

  • Describe the role of the Toll-like receptor (TLR) pathway in innate immunity.

  • Infer what types of immune-related molecules and genes a particular animal would have.

Question 1

Describe three characteristics of innate immunity and adaptive immunity that distinguish them from each other.

Innate immunity is nonspecific, acts rapidly, and recognizes broad classes of molecules. Adaptive immunity is specific, acts more slowly, and is longer lasting.

Question 2

Some people have a rare genetic disease that results in defective signaling in the TLR pathway. What would be the phenotype of such individuals?

The TLR pathway is involved in innate immunity to bacterial infections. Bacteria have molecules that act as pathogen-associated molecular patterns (PAMPs), and these normally activate the TLR pathway which results in white blood cells producing cytokines and other defensive molecules. If this does not occur, people will be especially susceptible to bacterial infections.

Question 3

If you compared the genomes of an insect and a human with regard to the presence of genes involved in immunity, what might you find?

The genomes of both the insect and the human would have genes for innate immunity, such as barriers and the TLR pathway, but only the human would have genes for adaptive immunity: antibodies, T cell receptors, and T and B cells.

The outcome of an infectious disease—the life or death of the host—often depends on the success of both rapid, innate responses and long-lasting, adaptive responses to invading pathogens. We will turn now to the innate defenses that protect vertebrates from disease.