Immunology question (bio)

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amybower
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hello! I'm currently preparing for a-level biology and I just thought of a question I can't find the answer to online. if antigens are what stimulate an immune response, why haven't pathogens just evolved to not have antigens? surely this would make them far more effective at spreading disease, as they'd go unchecked?
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becausethenight
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Good question! Basically, if you think about what an antigen is, it's going to be a protein in the cell surface membrane than an antibody can bind to. That protein will be useful or necessary to the pathogen - for example, it might allow a virus to enter a host cell. Pathogens can't really evolve to have naked cells, as then they would be unable to communicate with other cells (and therefore invade/disrupt host cells) Some sort of do, if you think about antigenic concealment in malaria, where Plasmodium. hides in human erythrocytes during part of its life cycle so its antigens aren't visible to the immune system.

Also (going a bit beyond A level) part of our immune system (the innate immune system) responds not to specific pathogens, but pathogens generally, and part of that is due to a special class of receptors, called toll-like receptors, on macrophages which bind to parts of the pathogen which are highly conserved (don't change/evolve), like the peptidoglycans in a bacterial cell wall, and then trigger the macrophage to destroy the pathogen. Bacteria can't really evolve not to have peptidoglycan cell walls, as without them, they'd be unable to maintain their internal pressure and just break apart (lyse).

I hope that was helpful
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amybower
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#3
Report Thread starter 1 year ago
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(Original post by becausethenight)
Good question! Basically, if you think about what an antigen is, it's going to be a protein in the cell surface membrane than an antibody can bind to. That protein will be useful or necessary to the pathogen - for example, it might allow a virus to enter a host cell. Pathogens can't really evolve to have naked cells, as then they would be unable to communicate with other cells (and therefore invade/disrupt host cells) Some sort of do, if you think about antigenic concealment in malaria, where Plasmodium. hides in human erythrocytes during part of its life cycle so its antigens aren't visible to the immune system.

Also (going a bit beyond A level) part of our immune system (the innate immune system) responds not to specific pathogens, but pathogens generally, and part of that is due to a special class of receptors, called toll-like receptors, on macrophages which bind to parts of the pathogen which are highly conserved (don't change/evolve), like the peptidoglycans in a bacterial cell wall, and then trigger the macrophage to destroy the pathogen. Bacteria can't really evolve not to have peptidoglycan cell walls, as without them, they'd be unable to maintain their internal pressure and just break apart (lyse).

I hope that was helpful
thank you!!
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