This chapter is not a comprehensive review of immunology but rather a condensed version of those aspects of immunology that have particular relevance to clinical immunology. Refer to the Bibliography for a more extensive discussion of the role of each component.
It is generally believed that the immune system evolved as the host's defense against infectious agents, and it is well known that patients with deficiencies in the immune system generally succumb to these infectious diseases. However, as we shall see, it may well play a larger role in the elimination of other foreign substances, including tumor antigens or cells and antibodies that attack self.
An immune response may be conveniently divided into two parts: (1) a specific response to a given antigen and (2) a more nonspecific augmentation to that response. An important feature of the specific response is that there is a quicker response to the antigen during a second exposure to that antigen. It is the memory of the initial response that provides the booster effect.
For convenience, the specific immune response may be divided into two parts: (1) the humoral response and (2) the cellular response to a given antigen. As we shall see, however, both responses are mediated through the lymphocyte. Humoral responses are antibodies produced in response to a given antigen, and these antibodies are proteins, have similar structures, and can be divided into various classes of immunoglobulins. Cellular responses are established by cells and can only be transferred by cells. (See the Bibliography for the extraordinary beginnings of the concept of a cellular arm of the immune system.)