Immunity system complexity: two-way defense (Introduction)

by David Turell , Saturday, June 13, 2020, 01:19 (1412 days ago) @ David Turell

Immunity cells respond in two ways depending upon the infection and where it is located, in or outside of cells:

https://www.sciencedaily.com/releases/2020/06/200612120148.htm

"Viruses and other disease-causing microbes influence the type of immune response their hosts will develop against them. In some cases, the predominant response involves antibodies, proteins made by the immune system that specifically recognize parts of the invading microbe and mediate its destruction. In other cases, immune cells are trained to recognize the microbe and lead the attack against it.

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"Research has shown that two factors related to microbes significantly affect the type of immune response that will predominate. On one hand are the microbial components (parts of proteins or genetic material, called pathogen-associated molecular patterns or PAMPs), and on the other is the location of the microbes, whether they tend to be inside or outside cells. Cells have means to recognize PAMPs ? some cellular proteins recognize PAMPs inside cells, while others detect PAMPs outside cells.

"Research on viruses has shown that when viral genetic material is detected inside cells, a cell-mediated immune response develops, while the detection of viral proteins outside the cell triggers antibody-mediated responses.

"The implementation of these immune responses involves cellular proteins called Pattern Recognition Receptors, or PRRs. Antigen-presenting cells, such as dendritic cells, are involved in the first steps of developing a specific immune response. During these first steps, antigen-presenting cells sample both the intracellular and extracellular environments by binding PAMPs to their PRRs. Recognition of a PAMP by a PRR turns on the danger alarm and alerts the rest of the immune system to the presence of a foreign microbial invader.

"In addition to these well-studied signals that mediate classic immune responses, Baylor researchers have proposed and demonstrated a different mechanism that directs the immune response toward a cellular type. This new mechanism also involves surveillance of both the intracellular and extracellular environments but by a different class of proteins called the Major Histocompatibility Complex, or MHC. MHC Class I binds protein fragments found inside of cells whereas MHC Class II binds protein fragments present on the outside of cells.

"'This mechanism appears to take place mostly when a fulminant viral infection occurs," said Decker, associate professor of pathology and immunology and corresponding author of this work.

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"'We found ample evidence that supports the novel mechanism and described a large molecular sensor complex we propose plays a central role in comparing the amino acids sequences of intracellular and extracellular protein fragments," said Halpert,

Comment: These kinds of interlocking defense systems require careful design, with especial care not to allow attacks on one own's tissues, especially when the virus is located intracellularly. This is not something 'cell committees' can develop, since the mechanisms must be present when the organism first appears in evolution. Survival depends upon it.