There are 2 branches to the immune system, the specific (adaptive) and non-specific (innate). The non-specific or innate part of the immune system is immediate i.e. it is the quickest to response but not very specific to any type of infection. Due to its unspecific response, the innate immune response is usually not enough to contain the infection, that is to say putting an end to the infection or at least bringing it under control. That is where the specific or adaptive part comes into play and this is what we will cover today.

B cells and T cells are the fundamental cells of the adaptive immune response. The adaptive immune response consists of Humoral Mediated Immunity, which is provided by B cells, in addition to Cell Mediated Immunity, which is provided by T cells. B cells secrete antibodies, specific to the antigen on the invading pathogen into the plasma of the blood and these antibodies recognize and attach themselves to said pathogen. However, if the infection has reached the inside of the cell, it is unreachable to these antibodies or in other words, Humoral Mediated Immunity is unable to take care of the issue. Then Cell Mediated Immunity takes over, in the form of T cell which destroys infected cells. In this way, these two immunities can protect the entirety of the body from attack!

Let us closer examine the steps in which B cells and T cells carry out their respective missions!

B cells

B cells produce and secrete antibodies into the blood plasma. In the previous video we covered how antibodies work in closer detail but for the purposes of this video it is enough to know that the paratope on the antibody binds to the epitope on the antigen which is a part of the invading pathogen. In the very first video of this immunology series, we covered what a pathogen is in detail but for now you can simply think of it as any foreign, infectious microbe which causes disease. As the antibodies bind to the invading pathogens they cause two main things to happen:

1. Agglutination, that is to say they cause pathogens to clump together and as a result immobilizing them.
2. Opsonization, meaning that they “mark” the pathogen for destruction or phagocytosis. This is done by simultaneously binding to the pathogen on one end and on the other end binding to one out of the many phagocytic cells that circulate the blood stream. These phagocytes are actually a part of the innate immunity so in this way adaptive and innate immunity collaborate to destroy the pathogen.

T cells

When a cell becomes infected, cell mediated immunity jumps into the action. The T cell responds by killing the infected cell. Several types of T cells exist including the y8 T cell, the CD4+ T cell and the Natural Killer T cell (which may I just say is probably the most badass name of anything that exists in the human body). However, the perhaps most common T cell is the CD8+ T cell, also known as the CD8 cytotoxic T cell. These T cells are called cytotoxic because of their ability to kill other cells. In other words, if a cell has gotten infected by a virus for example, the CD 8 cytotoxic T cell will come along and destroy the entire cell. This will prevent the virus from replicating itself since it requires a cell from the human body to do so. What’s perhaps even cooler is that while it is generally not enough to rid the body of cancer, cd8 cytotoxic T cells are also able to kill cancer cells.

So, earlier I mentioned that this adaptive immune response is specific. But what does that mean exactly and why is that the case? Well, simply put the antibodies that are produced by the B cells are specific to the invading pathogen. This means that, if we were exposed to a different pathogen or this same pathogen would mutate enough to change the structure of its antigens, these same antibodies would no longer be useful. This same kind of specificity is true for T cells as well, meaning that T cells are only able to respond to one type of pathogen.

Background image thanks to: dgim-studio on freepik.com

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