Chlamydia can down-regulate the expression of host cell MHC I and II by degradin

Question

Chlamydia can down-regulate the expression of host cell MHC I and II by degrading RFX-5 and USF-1. Describe two potential strategies that a virus may use to block or reduce MHC I presentation of viral peptides. "The administration of antimicrobial agents (antibiotics) might be altering the development of protective immunity to Chlamydia in the human population". Why is the use of antibiotics altering the protective immunity of a population of people? (think about disease progression with and without antibiotics, and developing immunity to Chlamydia in both of these situations.

Explanation / Answer

11.

Viruses are absolute intracellular parasites. They require a host for their replication. Since they are intracellular parasites, vertebrate immune system has evolved to combat such intracellular parasites. The machinery that is involved in processing and presentation of intracellular antigens/pathogens is called proteasome complex. This is a large multiple subunit complex which recognizes ubiquitinated proteins in a normal cell and digest them. Virus infected cells have a different composition of proteasome complex which generates peptide fragment of different properties.

These peptide fragments are displayed on the cell surface, carried by the class I MHC molecules. Class I MHC are expressed by all nucleated cells and they generally present peptides of the cell origin, to immune cells. They do so to show the immune cells that the cells are at normal function.

Infected cells have altered peptides displayed with their MHC – I. Thus, they become targets for T cytotoxic cells. These are also called CD8+ T cells which recognize virus infected cells and destroy them.

Virus employ the following mechanisms to block or decrease MHC-I expression:

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