Immune System
Word up homeys, dis section is the sickest…
Evert moment of every day there are millions of bacteria and viruses and the like, all trying to get in your body. They want to do this because it is what they do; it is how they survive, by feeding off you, or by hijacking your cells (is everyone getting nice and paranoid now?). The only thing is that this can often make you ill, or dead (not sure if philosophically this would be classed as very ill, or no longer ill…discuss) and so its very fortunate that we have an immune system, which fights infection.
The first defence against infection are barriers, such as the skin, which try to block the entry of infection into the body. Clearly there are gaps in this defence, such as if you get a cut and also through places like your mouth and your anus (let’s not get these confused…it could get messy).
The next steps of defence aim to either destroy the infecting microbe, or to destroy any cell which may have become infected. This latter point is important because Viruses work by getting inside one of your cells and reproducing lots of times inside the cell, before bursting out and causing mayhem. Two immune responses respond to infection and both work by immune response cells binding to specific structures (antigens) on the surface of the microbe or infected cell. However, the innate immune response responds to a general set of antigens, while the adaptive immune response responds to specific antigens.
The second step of defence is the innate immune response. The area inflames, swelling and going red, as blood flow is increased. This increased blood flow means that more antiviral defences can access the infected area quickly. Next up and complement proteins (eg antibodies) bind to the infected/infectious cell, marking it out. White blood cells (leukocytes) then identify the cells to be destroyed and move in. Leukocytes include macrophages and neutrophils (which engulf and eat the marked out infectious cell – these are called phagocytes). Other leukocytes called natural killer cells (coolest name of any immune cell), release chemicals near the infected cell, causing the cell to burst, or to self-destruct (apoptosis).
The third step of defence is the adaptive immune response. This response allows infectious cells to be remembered from previous encounters and then efficiently combatted. Types of leukocytes called lymphocytes are involved here and include B cells and T cells. B cells have antibodies on their surface, which bind to an infectious cell, if it has a specific characteristic (antigen) on its surface. The B cell then signals, attracting helper T cells, which activate the B cell and make it divide and in so doing are secreted millions of copies of the antibody which specifically binds to the surface of that particular type of infectious cell. The phagocytes of the innate immune response can then move in and do the dirty work (how clever is that then!!!). Killer T cells recognise specific target antigens on an infected cell (similar to the B cell) and respond in a similar way as the natural killer cells of the innate immune response. Killer T cells can be guided by helper T cells.
If the body has been infected by a particular infection before, B cells and T cells will already exist, which will be able to quickly identify the relevant antigen on the infectious microbe or infected cell. If the body has not been infected by a particular infection before, it takes more time for the B cells and T cells to establish what the relevant antigen is, on the infectious microbe or infected cell, but once this is done, the infection can be quickly combatted and the relevant antigen can be remembered.
Evert moment of every day there are millions of bacteria and viruses and the like, all trying to get in your body. They want to do this because it is what they do; it is how they survive, by feeding off you, or by hijacking your cells (is everyone getting nice and paranoid now?). The only thing is that this can often make you ill, or dead (not sure if philosophically this would be classed as very ill, or no longer ill…discuss) and so its very fortunate that we have an immune system, which fights infection.
The first defence against infection are barriers, such as the skin, which try to block the entry of infection into the body. Clearly there are gaps in this defence, such as if you get a cut and also through places like your mouth and your anus (let’s not get these confused…it could get messy).
The next steps of defence aim to either destroy the infecting microbe, or to destroy any cell which may have become infected. This latter point is important because Viruses work by getting inside one of your cells and reproducing lots of times inside the cell, before bursting out and causing mayhem. Two immune responses respond to infection and both work by immune response cells binding to specific structures (antigens) on the surface of the microbe or infected cell. However, the innate immune response responds to a general set of antigens, while the adaptive immune response responds to specific antigens.
The second step of defence is the innate immune response. The area inflames, swelling and going red, as blood flow is increased. This increased blood flow means that more antiviral defences can access the infected area quickly. Next up and complement proteins (eg antibodies) bind to the infected/infectious cell, marking it out. White blood cells (leukocytes) then identify the cells to be destroyed and move in. Leukocytes include macrophages and neutrophils (which engulf and eat the marked out infectious cell – these are called phagocytes). Other leukocytes called natural killer cells (coolest name of any immune cell), release chemicals near the infected cell, causing the cell to burst, or to self-destruct (apoptosis).
The third step of defence is the adaptive immune response. This response allows infectious cells to be remembered from previous encounters and then efficiently combatted. Types of leukocytes called lymphocytes are involved here and include B cells and T cells. B cells have antibodies on their surface, which bind to an infectious cell, if it has a specific characteristic (antigen) on its surface. The B cell then signals, attracting helper T cells, which activate the B cell and make it divide and in so doing are secreted millions of copies of the antibody which specifically binds to the surface of that particular type of infectious cell. The phagocytes of the innate immune response can then move in and do the dirty work (how clever is that then!!!). Killer T cells recognise specific target antigens on an infected cell (similar to the B cell) and respond in a similar way as the natural killer cells of the innate immune response. Killer T cells can be guided by helper T cells.
If the body has been infected by a particular infection before, B cells and T cells will already exist, which will be able to quickly identify the relevant antigen on the infectious microbe or infected cell. If the body has not been infected by a particular infection before, it takes more time for the B cells and T cells to establish what the relevant antigen is, on the infectious microbe or infected cell, but once this is done, the infection can be quickly combatted and the relevant antigen can be remembered.