Your immune system is a network of different organs and tissues that fights infection and disease. The immune system keeps a record of which microbes your body has defeated by developing memory cells. These white blood cells can attack and destroy invaders quickly, which helps your body develop long-term immunity. The immune system is responsible for fighting common colds, but there are many types of viruses that can infect your body. Catching one virus does not give you immunity against others.
The B lymphocytes secrete antibodies when they spot a particular antigen. Antibodies are special proteins that lock onto specific antigens. Each B cell produces only one specific antibody. The antibodies recognize specific pathogens and destroy them. They also recognize common cold viruses and other bacteria, and they act as markers for other immune cells. The immune system also has other types of cells called macrophages, which engulf and neutralize pathogens, such as fungus and bacteria.
The skin is the largest organ in the immune system. It covers the entire body and serves as an important barrier to foreign invaders. Lymphocytes help the immune system attack invaders and produce antibodies, while B lymphocytes alert T lymphocytes to destroy them. While T lymphocytes help the immune system fight disease, they do not make antibodies themselves. The spleen and lymph nodes filter blood and lymph.