Final answer:
White blood cells that are part of the immune system and circulate in the bloodstream are called lymphocytes.
Step-by-step explanation:
White blood cells that circulate in the bloodstream and are an important part of the body’s immune system are called lymphocytes. These cells include B lymphocytes (B cells) and T cells, which are crucial for specific immunity. B cells defend the body against specific pathogens by producing antibodies, whereas T cells destroy infected cells or regulate immune responses.
White blood cells can be classified as granulocytes or agranulocytes. Granulocytes, like basophils and eosinophils, contain visible granules and are involved in inflammatory and allergic responses. In contrast, agranulocytes, such as lymphocytes and monocytes, do not contain granules and have a variety of roles in the adaptive immune system and in phagocytosis.
Leukocytes, or white blood cells, are our body's primary defense system against disease, actively patrolling the blood and tissues to combat foreign invaders. White blood cells are part of the body’s immune system, destroying and removing old or abnormal cells and cellular debris, as well as attacking pathogens and foreign substances.