Chapter 3 – Immune System Basics

Publisher Summary The immune system is a complex set of tissues with mobile elements, whose function is to protect the organism from invasion by exogenous microscopic life. The immune system is composed of a variety of cell types, which form its major organs and circulate through vast networks of lymphatic and blood vessels. The immune system must detect invaders and abnormal cells to accomplish its task of protecting the individual from microscopic invaders or abnormal cells arising within the individual. The various cell types that make up the immune system are classified according to size, shape, appearance, staining properties, and functional properties. The switching of genes on and off is the fundamental mechanism whereby stem cells differentiate into the various immune tissue cells, alter their functional state, destroy themselves, or even become transformed into abnormally functioning malignant cells. Neutrophils are granular leukocytes possessing a nucleus with three or more lobes. They are short-lived cells. Eosinophils are cells that contain granules and irregularly shaped nuclei. Monocytes have nuclei with a more regular appearance that gives the impression of being folded. They also contain granules, which can destroy bacteria after they are ingested by the monocyte.