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The staggering complexity of the human Immune system reveals a constant struggle against all sorts of infectious agents such as: bacteria, virus, fungus, and parasites. I will break this essay into four parts:
A. How do humans prevent infection from happening?
B. Once infected what is the body’s first response (Innate Response)?
C. How do humans rid themselves of the infectious agent (Adaptive Immune Response)?
D. How does the immune system memory function?
A: The skin, nose hairs (both visible and microscopic), mucus, tears, and cilia lining the respiratory tract all work to prevent infectious agents from entering the body. Our skin is covered with harmless bacteria approximately 50 million to 5000 million per square inch. The nose traps and surrounds infectious agents with mucus, chemicals in tears prevent infection, and the cilia beating upward in the respiratory tract cleanse the lungs. A break in the skin, touching the nose, mouth or eyes with a hand which has touched virus, approximately 15, 000 of which could fit end to end on a pin head, can overwhelm the body. Inhaling virus infected droplets either coughed or sneezed out by an infected person could also overwhelm the body’s first line of defense.
B: Now let us say a person has been infected which we experience more than we realize. The immune system has two main types of White Blood Cells known as Neutrophils and Macrophages as part of what is called the Innate Immune response. Neutrophils are thought to be primarily involved with bacterial infections but Neutrophils may also be involved with viral destruction as well; however, Neutrophil response can lead to collateral damage due to activation of an inflammatory response which can be life threatening. Macrophages detect and engulf infected cells. Infected cells usually display changes on their surface which Macrophages detect. Some viruses have evolved a way to avoid having an infected cell display these surface changes, but in doing so lower the normal cell surface architecture which Macrophages can detect and thus destroy the infected cell. They evolve; we evolve as we face a never ending battle. Destruction of these infected cells limits viral replication since a typical infected respiratory cell could release about 10, 000 new viruses. Macrophages, once they have engulfed a virus infected cell, will then display viral antigens on their surface which will lead to another type of immune response call the Adaptive Immune Response.
C: The body being infected must begin a twofold attack on the invaders. With viruses, those virus particles roaming around the body in fluid such as blood or extracellular fluid must be destroyed. This is referred to as the humoral response. Also, cells which have been infected with the virus must be destroyed before the virus can replicate and release more viruses into the body fluid in order to infect more cells. This is referred to the cell mediated response. Remember that Macrophages displayed on their surface virus antigens once they had engulfed and killed a virus infected cell. This display of an antigen eventually promotes the production of B cells which start to produce specific antibodies which locate and mark the virus for destruction. This antibody antigen reaction eventually results in the destruction of the virus. The virus infected cells are also marked for destruction due to markers on the cell surface and these cells are destroyed thereby stopping further viral replication. There can be consequences to the battle being waged in the body. A variety of toxic chemicals can be produced such as histamine which can result in an inflammatory response which can lead to pneumonia. Also, the levels of the killings cells must be brought back down to a pre-infection level or else these may actually start an attack on healthy cells of the body inducing an auto-immune response where the immune system is attacking what it is there to protect. Fortunately, there are suppressor cells which normally control the level of killer cells after the infection has been controlled.
D: Once the invading agent has been destroyed, the antibodies which were produced remain in the body for months and therefore can quickly detect the same infectious agent and destroy it. Also, a variety of long lasting memory cell remain active in the body constantly circulating looking for the same infectious agent. These memory cells can quickly respond to the same infectious agent and stimulate very rapid antibody production. This is known as active acquired immunity which is what is produced by vaccination. This usually provides for lifetime immunity to that SPECIFIC virus or bacteria. Unfortunately, viruses such as the flu and common cold can mutate and require a new round of innate and adaptive immune response. Scientists have long been looking for some similar aspect of all existing common cold viruses and flu viruses which could be targeted so as to be an effective vaccine for all cold and flu viruses.
Typical Time Line of Viral Infection
Day 0 - you have been infected with a virus and have no symptoms but you are contagious
Day 1-4 - typical symptoms appear, fever up to 102 F, coughing, tired due to onset of the Immune response. The Innate Immune system has already been initiated and the Adaptive Immune system is at work performing both the Humoral and Cell Mediated Responses. You are most contagious now as you are coughing and sneezing out virus laden droplets.
Day 5-7 - you are feeling better fever still present but going down. Less contagious but the recommendation is that you wait 24 hours after body temperature is back to normal before interacting with others.
Day 7-10 - the virus has been neutralized but there are still many immune actions being taken by the body. Different classes of antibodies are being produced with a maximum of these present at about 14 days after Day 0. These will persist for months in the blood plasma. The inflammation is being attended to so you may still be coughing up mucus.
Try to think of the face as the deadly Bermuda Triangle. Imagine a triangle extending from above the eyes down to the chin. These are areas to be avoided especially the nose through which most viruses gain entry into the body!
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Note: Here's a follow up from my brother:
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Note: Here's a follow up from my brother:
The CDC reported for the 2018-2019 flu season of which they have real data over a period of time from Oct to March, that somewhere between 35 million to 50 million cases of the flu in the US! 500,000 to 600,000 hospitalizations and probably 35,000 deaths with 92% of deaths involving people with diabetes. How come this level of infection doesn't seem to overwhelm the medical profession?
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