Question

Describe one invertebrate mechanism of defense against pathogens and discuss how it is an evolutionary adaptation retained in vertebrates.

Short answer

Toll-like receptors are used in invertebrates to fight against microbial infection. These receptors activate the antimicrobial peptides in invertebrates which kills the pathogens. These toll-like receptors are retained in mammals as hybrid functional receptors.

Step-by-step solution

Immune system in invertebrates

Invertebrates exhibit an innate immune system and do not show the presence of an adaptive immune system. Physiochemical barriers and cellular defense systems fight against microbial infections. The encapsulation mechanism eliminates the multicellular parasites.

Toll-like receptors

The receptors of the innate immune system and one of the types of pattern recognition receptors are known as toll-like receptors. They work on sensing the molecular pattern. These are type 1 transmembrane proteins.

Recent studies have shown that toll-like receptors are present from annelids to mammals.

Function of toll-like receptors in mammals and invertebrates

The toll-like receptors are responsible for pathogen recognition and signal transduction. The recognition triggers the innate immune system in invertebrates which results in the secretion of antimicrobial peptides.

In mammals, these receptors are found in pattern recognition receptors as hybrid forms due to the presence of an adaptive immune system. For example, mammalian TLR4 detects the lipopolysaccharide of gram-negative bacteria.

The other function of toll-like receptors in mammals is bridging innate and adaptive immunity, proliferation, recognition of infected cells, and cytokine production and chemokines.