The complex physiological mechanisms involved in the immune system are not yet fully understood, but they continue to be unraveled by ongoing medical research. The immune system has six major components, three of which are different kinds of cells and three of which are soluble proteins. All six components can be found circulating in the blood in some form. Granulocytes are the most numerous nucleus-containing cells in the blood. Like granulocytes, they ingest foreign substances, interact with immunoglobulin and complement proteins, and carry potent enzymes in their cytoplasm.
Lymphocytes are, in some respects, the most important cells in the immune system.
B lymphocytes and T lymphocytes. T lymphocytes make up perhaps 70 percent of all lymphocytes. This immense diversity characterizes the immune system as a whole. The cytokines are soluble components that are largely responsible for regulating the immune response. Some cytokines amplify or increase an ongoing immune response, others instruct cells to proliferate, and still others may suppress an ongoing response.