Immunology and Cell Biology

Innate Immunity: An Emerging Science

The immune system is the collection of cells, tissues and molecules that protects the body from numerous pathogenic microbes and toxins in our environment. This defense against microbes has been divided into two general types of reactions: reactions of innate immunity and reactions of adaptive immunity. Thus, innate and adaptive immunity can be thought of as two equally important aspects of the immune system. As you will see, each aspect differs with respect to how quickly it responds and for how long it responds to pathogens, its central effector cell types and its specificity for different classes of microbes. As its name suggests, the innate immune system consists of cells and proteins that are always present and ready to mobilize and fight microbes at the site of infection. It thus provides an immediate response to foreign invader.

The main components of the innate immune system are 1) physical epithelial barriers, 2) phagocytic leukocytes, 3) dendritic cells, 4) a special type of lymphocyte called a natural killer (NK) cell, and 5) circulating plasma proteins. Innate immune responses are not specific to a particular pathogen in the way that the adaptive immune responses are. They depend on a group of proteins and phagocytic cells that recognize conserved features of pathogens and become quickly activated to help destroy invaders.