Immunology 101
learning more about the immune system
To really understand the complexity of the immune system would likely require a multi-week, college level course with a strong foundation in biology as a prerequisite. With that said, we will try to simplify it as much as possible…and probably oversimplify it for biology majors and doctors (who should probably skip this section, unless they like to complain and make fun of simple internet posts).
The immune system is a complex network of organs, cells and proteins which defends a living organism, like us, from infections. Infections can be caused by viruses (which are non-living packets of DNA or RNA which replicate within host cells to create more viruses), bacteria (which are single non-nucleated cells capable of dividing and growing rapidly and typically much smaller than nucleated cells that humans have), or parasites (which are more complex organisms that can be single cells, like amoebas, or multicellular, like worms or fungi).
Many types of cells mediate the immune response. These are typically white blood cells (WBCs) that circulate throughout the body. White blood cells may reside in certain organs like the spleen and lymph nodes. They can also travel throughout the body in the blood stream and lymphatic system. When the body senses an infection, the white blood cells will migrate to the site of infection and then multiply rapidly to fight the infection. There are 5 main types of WBCs: lymphocytes, neutrophils, eosinophils, basophils, and monocytes. Each cell type serves a different function depending on the type of reaction and phase of the immune response.
Within the lymphocyte class of cells, there are T-cells and B-cells. There are several types of T-cells, but their primary function is to either directly attack infected cells or coordinate the other immune cells’ response. B-cells fight infections by creating antibodies, which are large molecules made of protein, designed to recognize specific components in an infection. A protein is made up of a sequence of amino acids, which is coded for by our genes (DNA/RNA). The sequence of amino acids determines the folding and shape of the protein. The shape of the protein determines a protein’s function. The basic shape of an antibody protein looks like the letter “Y”, with the upper tips of the “Y” designed to recognize some part of the offending infection which is not suppose to be present in the body. There are 5 classes of antibodies: IgG, IgM, IgA, IgD and IgE. Each class of antibody serves a specific function depending on the phase and location of the infection. For instance, IgM is commonly produced early in an immune response and is made of five “Y” shaped proteins arranged in a pentagon pattern. Antibodies tag and coat the surface of infections which make it easier for the immune system to attack the infectious process.
What is remarkable about antibodies and the immune system is how specific the recognition of an infectious process needs to be in order to mount a proper response. In order to fight infections, our immune system looks for “antigens” which are foreign substances which enter the body and are recognized as products of an infection. The number of possible antigens which the immune system might recognize is enormous. Also, the difference between an antigen and normal protein might be very subtle. Somehow, the immune system throughout our lifetime has to learn what it should attack and what it should not attack. When we get a vaccine, we are presenting the immune system with antigens to train it to mount a proper response to certain infections such as polio or measles, without the need to suffer from the infection. Antibodies have become important in the biotechnology industry, due to their ability to recognize substances very specifically on a molecular level. Antibodies can be trained to recognize substances to allow for improved diagnostics and therapeutics in many diseases.
Sometimes, the immune system accidentally learns to attack parts of the body that it should not, leading to a class of diseases called “autoimmune” diseases. Rheumatoid arthritis is a type of disease in which the immune system attacks a person’s joints. Other common forms of autoimmune diseases include systemic lupus erythematous, scleroderma, multiple sclerosis, and type 1 diabetes. Also, the exquisite sensitivity of our immune system is one of the main problems when we transplant organs since often the immune system “sees” the new organ as something filled with new antigens which needs to be attacked.
Food allergies are also a type of improper immune response. It is unclear why the immune system of some people recognize food as foreign antigens which might trigger an adverse response. Some people theorize that improved sanitation is a cause, which might result in our immune system “searching” for something else besides infections to respond to. Another theory is that increased use of genetically modified foods, have resulted in a greater number of new antigens which the body is not accustomed to recognizing. Again, these are theories which have not been definitively proven.
Any adverse effect caused by the immune system and triggered by food is considered a food allergy. However, IgE-mediated food allergies are the most concerning due to the speed and severity of the reaction. It is believed that the IgE antibody’s main purpose is to fight parasitic worm infections, which are not as common in modern times. When an IgE antibody recognizes an antigen, it then binds to types of WBCs called mast cells and eosinophils. This results in a release of histamines from the cells, which triggers an inflammatory response. Mild histamine release may result in itchy skin or runny nose. “Hay fever” which is an allergic reaction to pollen, is a mild histamine reaction, which is why antihistamines such as Benedryl or Claritin can be helpful. Mores severe histamine reactions include asthma, hives or anaphylaxis. To learn more about anaphylaxis, click here.
One of the ways to diagnose food allergies is with a blood test which measures a person’s IgE levels to specific types of food. The higher a person’s total IgE level is, the greater the probability of having any type of allergy. A doctor who specializes in allergies (allergist) can order a person’s total IgE level, as well as IgE levels reactive to specific types of food, like wheat, egg, nuts, etc.
Our immune system is an incredibly complex, and from a biology standpoint, beautiful system. A few paragraphs hardly does it justice. If you are interested in more information, here are some additional resources.
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https://www.ncbi.nlm.nih.gov/books/NBK279364/
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https://my.clevelandclinic.org/health/body/21196-immune-system
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