Chapter 1: The Need for Self-Recognition

Unit I: Introduction This dictum—short in length but deep in meaning—encapsulates a basic need for all forms of life. In a way, most organisms in our world live alone. They are composed of single cells or particles, and as such, their need to distinguish themselves is seemingly simple. Their single cell or particle is “I,” […]

Chapter 2: Antigens and Receptors

Overview Immune responses are initiated by the interaction between a ligand and a receptor protein on the cell’s surface of a soluble receptor. These interactions trigger the activation of leukocytes or white blood cells. The complementary shapes of the ligand and its receptor are critical. The effectiveness of interaction often increases with the affinity or […]

Chapter 3: Barriers to Infection

Unit II: Introduction Our initial immune defenses rely on types of cells and molecules that have performed admirably for hundreds of millions of years. Early in the history of life, organisms developed mechanisms to ask whether a particular cell was “self or nonself” and “friend or foe.” As life diversified, different groups of organisms developed […]

Chapter 4: Cells of the Innate Immune System

Overview White blood cells or leukocytes serve as sentinels and defenders against infection by patrolling the tissues and organs of the body. They move around the body via the lymphatic and blood circulatory systems and can leave and reenter the circulation to move through body tissues. As “soldiers” of the immune system, leukocytes have specialized […]

Chapter 5: Innate Immune Function

Overview If microbes should penetrate the body’s first line of defense—the mechanical, chemical, and biological barriers—the innate immune system provides the second line of defense (the first immunologic line of defense) against infection. Because its components are always in an activated or near-activated state, responses by the innate immune system occur much faster than those […]

Chapter 6: Molecules of Adaptive Immunity

Unit III: Introduction Eventually, some types of animals began to add even more items to their immunologic tool kits. These new tools enabled the body to supplement the innate immune system with a new set of protective mechanisms that make up the adaptive immune system. One of these new tools, appearing in organisms as ancient […]

Chapter 7: Cells and Organs

Overview In contrast to the morphologically distinct cells of the innate immune system, lymphocytes of the adaptive immune system generally look-alike except for size, ranging from small (4 to 7 ?m) to medium (7 to 11 ?m) to large (11 to 15 ?m). Lymphocytes may be broadly categorized by the antigen-specific receptors they generate through […]

Chapter 8: Generation of Immune Diversity: Lymphocyte Antigen Receptors

Overview Epitope specificity of immunoglobulin molecules produced by B cells and of T-cell receptors is determined before they encounter antigen. Moreover, several possible epitope-binding specificities greatly exceeds several genes within the human genome. This presents a paradox: How does the immune system generate a diverse array of antigen-specific molecules from a limited number of genes? […]

Chapter 9: Lymphocyte Development

Overview Epitope-specific T-cell and B-cell receptors (TCRs and BCRs) are randomly generated within individual thymus- and bone marrow–derived lymphocytes by gene rearrangement. Not surprisingly, some lymphocytes develop receptors that react with self epitopes. However, a selection mechanism is in place that removes these cells before they become fully functional and attack the body’s own and […]

Chapter 10: Lymphocyte Activation

Overview Compared with innate immune responses, adaptive immune responses against newly encountered antigens initially develop slowly. Although many self-reactive cells are eliminated during development, lymphocytes undergo a further set of time-consuming checks and balances to minimize the potential for adverse immune responses. This system of checks and balances is imposed by different cell types for […]