Immune response, antigens, antibodies, B-cells and T-cells

Created April 2020, Offline version here
Video by Paul Anderson, also on his website Bozeman Science.

    Bacteria, viruses or other infectious agents, known as , are constantly attacking our bodies. However, healthy individuals seldom experience severe symptoms after the first infection.
    This is largely in part due to the immume system and its response. There are two basic, general types of immune responses: non-specific and specific. Non-specific immune response responds to all foreign bodies that are not native to the body itself whereas specific immune response targets the “specific” invaders. Examples of non-specific immune response include: acting as an exterior barrier, inflammatory response to of surrounding tissue, and macrophages engulfing foreign bodies. In particular to macrophages, it does not discriminate against any foreign body in that it will attack anything that it recognizes as not its own. This may pose some trouble if say, a person were to receive any organ impants as the body will reject the foreign tissue.
    While the non-specific immune response does not target particular types of invaders, the specific immune response does. The specific immune response is the line of defense and often the last, if the invaders were able to get past the skin, macrophages and the inflammatory response.
    This type of response employs the use of antibodies against the antigens. Antibodies are made of .
    As the name suggests, each antibody is specific to one type of antigen and can only bond with that specific type. The general shape of the antibody is forked or Y-shaped and the tips of the forks have different shapes that the antigen shape. How the antibody helps to attack invaders is by bonding to the antigen, which then it acts as a flag and identifies the antigen to be foreign invader. Macrophages then can respond to the flags and proceed to engulf the antigen. Multiple antibodies can also bond to the antigen which can physically slow down the antigen function.
    While the antibodies play an important role in the specific immune response, we also have to look at some steps the precedes the antibodies as well as cells that are a part of this response. There are two types of lymphocytes, or , that take part in the response: the B-lymphocyte and T-lymphocyte. B-lymphocytes are manufactured in the bone, hence the prefix B, and are a part of the humoral response.
    Humoral response refers to any immune response that occurs in the body’s such as the blood or the lymphatic fluid. B-lymphocytes manufactures antibodies by using naïve B-cells.
    These naïve B-cells can sense the shape of the antigen and then produce the corresponding antibody that complements that shape. In addition to the production of antibodies, B-cells also produce . These to defend the body from future infections caused by the same bacteria or virus.
    T-lymphocytes, or T-cells, are produced in the gland, located behind the breastbone, hence the prefix, T. T-cells are a part of the cell-mediated response in that they only respond to another cell’s signal. Their main function is to attack infected cells or even cancerous cells using a specific type of T-cells called killer T-cells. How the killer T-cells “kill” is to induce cell death or apoptosis. Another type of T-cell is the helper T-cell in that it “helps” to signal the B-cells to produce antibodies and macrophages to engulf the foreign bodies.
    To put the different pieces of the specific immune responses together, here is the process from the beginning of the infection to how the immune system responds to antigens: 1) the body becomes infected with an or an infectious agent, 2) macrophages engulfs or eats the antigen, 3) pieces of the antigen are presented on the surface of the macrophage using a chemical called , 4) helper T-cells senses the piece of antigen and uses to sense the antigen shape to communicate to B-cells to make antibodies, to signal killer T-cells, and to signal other macrophages to target antigens.
    Part of the immune response is to gain “memory” from the initial exposure so that the body can gain immunity to future infections. After the exposure to the antigen, the person will experience symptoms, in other words, the person is sick.
    While the person is experiencing symptoms, the body is actively fighting off the infection with the specific immune response, hence there is this lag time from initial exposure to sickness as the body responds to the antigen. Protective immunity comes from memory cells that are manufactured by that “remembers” the infection so the corresponding antibodies can be produced quickly to mark the antigen. However, people can become sick multiple times if there is a mutation to the antigen. As the antibodies are complementary and specific to the shape of the antigen, any mutation or conformational changes of the antigen will render the existing antibody useless. Therefore, the body will have to manufacture another set of antibodies and memory cells with the different types of infections.
    In summary, the immune response can be broadly categorized into two types: specific and non-specific. The two types can also be illustrated using a castle analogy where the castle walls represent the first line of defense, the , the guards of the castle represent the , and the spies of the castle represent the .
    Non-specific immune response include the skin, inflammatory response, and macrophages that engulf any foreign invaders. Specific immune response uses two types of lymphocytes, B and T, to combat antigens. B-lymphocytes, or B-cells, are produced in the bone marrow and are part of the humoral response, which refers to any response that occurs in bodily fluids. The primary function of the B-cells are to produce antibodies that help flag antigens and memory cells that gives rise to immunity. T-cells are produced in the thymus gland and it is part of the cell-mediated response. While the T-cell’s primary function is to kill, there are two types of T-cells: helper T-cells and killer T-cells. As the name suggests, the killer T-cells actively induces cell death to infected cells. Helper T-cells helps or mediates the production of antibodies, signal macrophages to target specific cells, and activates killer T-cells to kill. With the entire process of the specific immune response, people gain immunity to infections over time with the help of memory cells. However, if the infectious agent mutates, the existing antibody will be useless as the shape of the antibody will not match the new strain.