The main function of your immune system is to seek out and destroy foreign invaders to your body, including bacteria, viruses, fungi, parasites, and even cancer cells. These invaders carry antigens, substances that tell your body that they don’t belong there. Your body reacts by making antibodies to fight off the invasion. Special WBCs called B cells produce these antibodies, which bind to the invaders and signal other WBCs to come and destroy the invader. (Similarly to putting a flashing light on the head of someone in a crowd to signal others that this is the one.)
The following explanation of WBCs will give you a greater understanding of how your immune system works, so you can really understand this vital system God has blessed us with. The major categories of WBCs are:
1)   B cells
2)   T cells
3)   Granulocytes
      a) Neutrophil
      b) Basophilic
      c) Eosinophil
4)   Phagocytes
      a) Monocytes
      b) Neutrophil
      c) Macrophages
5)   Nonspecific effector cells
      a) Macrophage
      b) Neutrophil
      c) NK cell (natural killer)
B cells develop in bone marrow, and move into the spleen and lymph nodes to wait for their call to battle. B cells produce antibodies, which attach to bacteria, fungi and parasites, literally marking these invaders so that, the phagocytes — the “eating” WBCs—will know what to devour and destroy.
T cells detect viruses and other pathogens inside the body’s cells by reading the genetic code of the invader, which is different from our own. The T cell then transforms into different T cells, including the killer T cell that actually kills the infected cell. The inflammatory T cells also call the macrophages to come and devour the invader. Amazingly, T cells actually “remember” what the invaders “look” like, so they can quickly respond to future invasion attempts by the same invaders.
Neutrophils, in greatest supply in the body, eat bacteria, viruses and fungi that have been tagged with antibody for destruction. (Neutrophils will also eat invaders that haven’t been tagged with antibodies.) Eosinophils are much like the neutrophils, but more involved with destroying parasite intruders and regulating allergic reactions. Basophils are also involved with allergic responses, producing histamine, which is connected to most allergic symptoms.
Monocytes eat bacteria and fungi. They also mature to larger macrophages, which can devour the most bacteria and fungi—even whole RBCs and malarial parasites. Macrophages can eat up to 100 bacteria, five times as much as neutrophils. Macrophages clean up the body’s system by eating dead tissue and dead neutrophils, which usually die after eating 5-20 bacteria. Macrophages can live for months, even years, while average neutrophils and other WBCs live only 2-3 days. Some macrophages are stationary, staying in the spleen, lungs and lymph nodes, waiting for invaders to come to them; others roam through the blood tissues of the body, consuming any intruders they find.
NK cells (natural killers) seek and destroy cancer cells and virus-infected cells—without help from other WBCs. Cancer cells constantly form in our bodies, but a strong and healthy immune system can kill them before they multiply and form tumors.