The immune system is your body's defence mechanism against disease and sickness. Unless you live a sealed environment, your body is regularly exposed to viruses, bacteria, toxins and other micro-organisms that can enter your body that trigger disease, sickness or general ill health.
If your immune system is in good working condition, it responds to any of these invaders by attacking the virus, killing bacteria or eliminating toxins from your body. That's why health practitioners constantly remind patients to have a healthy diet, take multivitamin supplements and to exercise regularly to boost the immune system.
The lymph is a bodily fluid that transports various substances (interstitial fluid, including plasma protein and immune cells) to cells in the body, eventually ending in the lymph nodes for processing. When bacteria invade the body, it is transported to the lymph nodes where the body's cells fight with the bacteria, causing the lymph nodes to swell. Thus, swollen lymph nodes are good indicators of infection. When the body is able to fight bacteria on its own or with the help of antibiotics, the flow of lymph is restored and the swelling of the lymph nodes subside.
Major components of the immune system are the leukocytes or "white blood cells". White blood cells are produced in various parts of the body such as the bone marrow, thymus and spleen. White blood cells move around in search of viruses, bacteria and other invaders in your body. There are two types of leukocytes:
The bone marrow produces B lymphocytes. B lymphocytes act as the immune system's intelligence network. This type of lymphocyte searches for bodily invaders known as "antigens." When B lymphocytes detect the presence of antigens, they produce antibodies that attach to the antigen for proper destruction by another type of lymphocyte, the "T" cells.
T lymphocytes are white blood cells that mature in the thymus. Also known as "T" cells, T lymphocytes work by destroying antigens that the B lymphocytes have identified and locked on to.
Not all antigens are destroyed by the killer "T" cells. What is amazing about the immune system is that it retains some of the antibodies, to make your body ready to defend itself against a second or future invasion of the same antigen. So you can also develop immunity from certain diseases once you get them.
For example, when you get infected by chicken pox or measles, the antibodies produced as a result of the infection remain in your body. These antibodies arising from illness protect the body from future recurrence. For this reason, your doctor may tell you that you need not worry about getting the chicken pox or measles twice.
You need not be infected first in order to enjoy immunity. This is where immunization shots come in. An immunization shot contains a lose dose or less virulent strain of an antigen so as not to cause sickness or disease, yet sufficient for your body to produce antibodies that can eliminate similar viruses in the future. Vaccines are now readily available for most common diseases such as flu, measles, mumps, tuberculosis, polio and typhoid.