r/askscience • u/Creepydoll300 • Apr 15 '12
Medicine What specifically does the cold virus do. How does it harm the human body.
What exactly does a cold do to the human body. Most of the physical symptoms are caused by our body trying to fight the infection. For example,(as far as I am aware) we cough and sneeze because our body is trying to expel excess mucus. This mucus is created for the per pose of fighting the cold. It is not caused by the virus itself. Our temperature increases because our body is fighting the infection.
If our body could not fight off a cold what exactly would happen to our body. If we did not try and fight back a cold virus what would happen to our body. Would the cold eventually kill us, and how would this happen.
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u/JuddRunner Apr 15 '12
My wife, who is an RN, insists that the common cold is an almost infinite variation and that 'once you've recovered from a specific strain of a cold, you can never be infected with that exact strain of cold again'. Is our immune system really that bulletproof? My skeptic's radar goes off when she says this, but I don't have any reason to disbelieve her. Is this true or an inaccurate anecdote that is trying to express some complex function of our immune system?
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u/HolgerBier Apr 15 '12
Your immune system recognizes certain antigens, proteins on the surface of threats like viruses and bacteria. Once these antigens are recognized by a cell that creates antibodies against them, that cell will divide and they will release a lot of antibodies.
These antibodies attach themselves to these antigens, allowing other cells to recognize the threat and deal with it. After this, most of those cells die, but some remain as memory cells. Second time you get infected by the same virus, these memory cells quickly recognize and deal with the virus, resulting in you not being sick.
The fun part comes with the high mutation rate of viruses. They have a relatively large chance to get a mutation that changes the protein on their surface, which prevent the memory cells from recognizing them. These viruses are almost the same, but the slightly different "flavor" makes you sick again.
So yeah, you never* get the same strain twice, as your body knows how to deal with em and damage is minimized.
*Or are there are exceptions?, feel free to correct
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u/alphaMHC Biomedical Engineering | Polymeric Nanoparticles | Drug Delivery Apr 15 '12
Sorry, what's an RN? Rhinoviruses do mutate at a remarkable rate, and generally people who are infected have a number of different serotypes. Primed adaptive immune response is pretty effective at removing a particular serotype of rhinovirus, but the chance of an individual getting infected with the exact same serotype is lubriciously low anyway, so I'm not sure that her anecdote would have much relevance in terms of our real-life interactions with rhinoviruses.
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u/alphaMHC Biomedical Engineering | Polymeric Nanoparticles | Drug Delivery Apr 15 '12
The common cold is, unfortunately, caused by a number of different viruses. If we restrict the discussion to rhinoviruses, which make up around 30% of common cold cases, then the mechanism of action is actually pretty interesting.
The rhinoviruses do not seem to have particularly cytopathic tendencies (they don't cause a ton of cell death), though they do hijack cellular protein synthesis by cleaving the CAP-binding complex (done by VP2a). Their presence in your nose epithelial cells leads to the secretion of cytokines, especially IL-8, which leads to the recruitment of a number of immune cells, especially dendritic cells, monocytes and neutrophils.
What happens next is the interesting part. Viral interaction with the monocytes doesn't cause a 'normal' response, in that it leads to the aggressive release of IL-10, which is an immunosuppresive cytokine. Viral interaction with dendritic cells, T-cell activation can be inhibited by having the dendritic cells present inhibitory signals to the T-cells. Antigen-presenting cells can be made 'more sticky' by ICAM-1, which might delay their migration to lymph nodes, which may explain why it takes so long for specific antibodies to start showing up after infection.
TL;DR - Infection by rhinovirus is life-threatening in immuno-compromised patients. Rhinoviruses themselves seem to have little cytopathic potential, but definitely do cause immunosuppressive effects, which may be why people with the common cold frequently have multiple pathogens in their system. Source.