Immunisation Against Disease

The Immune System contains a highly complex system made up of special cells, molecules and tissues. It gives the human body protection against damaging or potentially life threatening viruses and bacteria’s. The bodies’ ability to defend against these germs is called immunity. Immunity is the ability to protect from highly infectious diseases and viruses that attack the human body.
The immune system contains white blood cells also known as leukocytes. White blood cells play a very important part in the bodies’ protection against disease. There are several different types of white blood cell, which all have factors in common with each other.

A lymphocyte is one of the most important special types of white blood cell. Lymphocytes first start life in the bone marrow, which is the tissue in the centre of the bone. They are then formed from stem cells. There are two main types of lymphocyte – B cells and T cells. B lymphocytes stay in the bone marrow and mature, while T lymphocytes are transported, through the bloodstream to the thymus gland, which is an organ situated above the breast bone, and they are then matured here. A lymphocyte cannot assist in the immune response unless is has been matured properly. Once they have been matured they then travel to the spleen. The spleen is the largest lymphoid organ in the body. It’s found on the left side of the body in the abdominal cavity between the stomach and the diaphragm. The spleen contains a white pulp, also called ‘splenic lymphoid nodules’ (www.wisegeek.com). This pulp associates with small nodules in the spleen that are very rich in B and T lymphocytes. The spleen also filters lymph fluid.

B lymphocytes and T lymphocytes work in slightly different ways.
T cells develop into two different kinds; helper T cells and killer T cells. Killer cells kill the cells that the virus or bacteria has already infected. They help stop the virus spreading throughout the rest of the body, while the B cells are making the antibodies.
The helper cells activate the B cells, and make them make necessary antibodies needed to fight the disease. They also help killer cells to develop. B lymphocytes work slightly differently. They produce antibodies. The type of antibody that the cell makes depends on the type of pathogen present. The antibody then attaches itself to the invading pathogen and destroys it. B cells, in some cases, are able to make a memory cell after the disease has been destroyed. A memory cell is vital for the bodies immune system, because if the memory cell then encounters the same pathogen again later on in life, it will react more rapidly because the cells already know what the pathogen looks like, so it will destroy it before the body even starts to feel any symptoms of the disease.

The primary immune response on the other hand isn’t as fast. This happens when the lymphocytes detect a pathogen that hasn’t been recognised. The B cells start making the antibodies to fight the pathogen, and this can take anything from seven to fourteen days to complete.
Plasma cells are a component of the immune system, and produce lots of antibodies at a very quick rate, releasing thousands of antibodies per second.
Artificially acquired active immunity is given by vaccination. The antigens of the disease are injected into the body. The immune system meets the disease, and then the lymphocytes attack it and create memory cells. The disease then won’t develop again because the memory cells recognise the antigen.

There is also naturally acquired active immunity, which is where the person has been exposed to the live antigen, and therefore develops the disease. Symptoms will develop, but the body will recognise the antigens and produce the primary immune response.

Another type of immunity is artificially acquired passive immunity. This is only short term, and it works by the injection of antibodies to help fight the disease. You can also get naturally acquired