The Immune System
The immune system is a system that protects the body from the harmful organisms, like bacteria, as well as non-living things, like viruses. Just like the other systems in the body, the immune system is really important. It’s there to make sure that the other systems can function well without being damaged or even destroyed by pathogens.

The immune system vs. Pathogens

Pathogens, or “specific microorganisms…that caused diseases”, damage the body and not letting it to regulate homeostasis (Nowicki 941). For example, when a person gets a fever, his body temperature increases and he loses homeostasis. Pathogens can cause serious damage of tissues, organs, or even systems. The immune system doesn’t want it to happen. The immune system will send white blood cells to destroy the pathogens (Nowicki 945). White blood cells can distinguish pathogens from normal cells by the antigens on the surface (Nowicki 951). When you’re looking at an inflammation, you’re actually looking at a large amount of white blood cells fighting the pathogens (Nowicki 950). While the immune system fight bacteria with antibodies, viruses don't have membrane for the antibodies to attach to. So, the body has a special way to fight viruses. Infected cells would produce a protein called interferon. This protein would send out alarms to normal cells to avoid the virus from reproducing (Nowicki 947). There are 2 main ways the immune system fight the pathogens: passive immunity and active immunity (Nowicki 948). In passive immunity, the body doesn’t make antibodies to fight the pathogens (Nowicki 948). The antibodies are either passed down from the last generation in DNA or from mother's milk (Nowicki 948) . In active immunity, the body sends white blood cells, like phagocytes, T cells, or B cells, to fight specific pathogens (Nowicki 948). Acquired immunity (a type of active immunity) is when the pathogens are memorized by the memory cells (Nowicki 951). The memory cells remember the pathogens from the last attack (Nowicki 951) or from vaccines, which contains the antigens of the pathogens (Nowicki 956), so if the same pathogens enter the body, it responses much faster.

The help from others:

Other systems play parts of the immune system. For example, the mucus membrane and hair in nose or the throat of the respiratory system trap the pathogens before they can enter the body (Nowicki 945). The acid in the stomach of the digestive system kill the pathogens that get into the stomach. Skin of integumentary system is a “physical barrier” that prevents pathogens from entering the body (Nowicki 945). During inflammation, the blood vessels of the circulatory system open holes letting the white blood cells out to the infected site (Nowicki 950). During a low fever, white blood cells are made and mature much faster (Nowicki 951).


T cells and B cells

T cell is a white blood cell that fights pathogens that already infect the body (Nowicki 946) during cellular immunity (Nowicki 952). They only fight the pathogen with certain antigens. They destroy both the pathogens and the infected body cells (Nowicki 952).
B cell is a white blood cell that fights the pathogens before they can infect the body (Nowicki 946). B cells produce a special protein called antibody that assists to fight the pathogens by three ways: they can attach to the membrane proteins of the pathogen and make them inactive; they help phagocytes by making the pathogens to clump; or they weaken the pathogens membrane by producing a complement protein (Nowicki 947). B cells functions in humoral immunity and have to be activated by T cells before functioning (Nowicki 953).


The other side of the immune system:

White blood cells can differentiate the body cells from foreign cells by the protein makers on the membrane (Nowicki 951). When an organ from a donor is inserted into the body, the immune system would recognize that it’s not the same and start to attack it (Nowicki 954). This is called tissue rejection (Nowicki 954).

Click on these links to explore more about the immune system:
Immunology Virtual Lab:
The Immune System:
Fighting Back:
Vaccine and Active Immunity:

Work Cited

Nowicki, Stephen. "Immune System and Diseases." McDougal Littell Biology. Evanston, IL: McDougal Littell, 2008. 938+. Print.