BIOL 1051H Chapter Notes - Chapter 21: Innate Immune System, Adaptive Immune System, Natural Killer Cell
Immune System
The immune system is that part of your body that specifically fights infection by
pathogens. There are two branches to the immune system in this regard. The innate immune
system if the part that is inherited and ready to go when you are born. The adaptive immune
system is that part that relies on lymphocytes and changes in its ability to fight pathogens
through exposure. Although you are born with the adaptive immune system, it really can’t do
anything to help protect you from a pathogen without first being exposed to it.
The innate immunity starts with the barriers previously discussed but extends to the
innate immune system which consists of an extensive series of cells and non-cellular
constituents. The innate immune system also distinguishes between the body’s own cells and
tissues, and those that don’t belong there. There are some attributes of pathogens that are
chemically reliable indicators that that cell is not one that belongs to the body. These are called
pathogenassociated molecular patterns or PAMPs. PAMPs are only found on pathogens.
Some cells are capable of recognizing PAMPs and will phagocytose or eat the offending
microorganism. Such cells are called phagocytes and there are several of them. Once
phagocytes find a microorganism they do more than just eat it. They also send out chemical
signals (cytokines) which call other phagocytic cells to the area and which begin the processes
of the adaptive immune system recognition. The table below shows a list of various phagocytic
cells and where they are found.
Viruses also have their own specific molecules on their surfaces which can trigger the
innate immune system but the best viral defense actually comes from virus infected cells. Such
cells will produce chemicals called interferons. These will change the behavior of neighboring
cells such that they are less likely to become infected with the virus. They also will call in the
immune system cells such as natural killer cells which will destroy the infected cell before the
virus can spread
The process of phagocytosis involves first attaching to and then engulfing the offending
organism (or particle). Once inside the phagocyte, the engulfed material will fuse with a
lysosome and will be broken down. Mostly the result of the actions of the innate immune system
is to produce inflammation. The hallmarks of inflammation are heat, redness, swelling, and pain.
Heat is caused locally by increased blood flow to the infected area. However, sometimes
the increase in heat is all over the body in the form of fever. The hypothalamus normally
controls body temperature but will respond to some chemicals by increasing the temperature set
point of the body. Local production of hormones such as endogenous pyrogen (an interleukin)
will cause temperature increase but so will bacterial LPS. Fever is a good thing in that most
bacteria are very sensitive to changes in temperature and will stop reproducing, if not outright
die in a warmer environment than optimal. As it turns out even cold-blooded animals such as
Document Summary
The immune system is that part of your body that specifically fights infection by pathogens. There are two branches to the immune system in this regard. The innate immune system if the part that is inherited and ready to go when you are born. The adaptive immune system is that part that relies on lymphocytes and changes in its ability to fight pathogens through exposure. Although you are born with the adaptive immune system, it really can"t do anything to help protect you from a pathogen without first being exposed to it. The innate immunity starts with the barriers previously discussed but extends to the innate immune system which consists of an extensive series of cells and non-cellular constituents. The innate immune system also distinguishes between the body"s own cells and tissues, and those that don"t belong there. There are some attributes of pathogens that are chemically reliable indicators that that cell is not one that belongs to the body.
