8.THE LYMPHATIC AND IMMUNE SYSTEMS

• Lymph and the Lymphatic Vessels
• Lymphatic Cells
• Lymphatic Tissues
• Lymphatic Organs
• Innate Immunity
• External Barriers
• Leukocytes and Macrophages
• Antimicrobial Proteins
• Natural Killer Cells
• Adaptive Immunity—General Aspects
• Forms of Adaptive Immunity
• Antigen-Presenting Cells
• Clinical Application: Lymph Nodes and Metastatic Cancer
• Clinical Application: Reye Syndrome
• Clinical Application: Asthma
• Clinical Application: Neuroimmunology and the Mind–Body Connection
• Cellular Immunity
• The most immediate requirement for dealing with tissue injury is to get defensive leukocytes to the site quickly.
• Cytokines usually act at short distances, either on neighboring cells (a paracrine effect) or on the same cell that secretes them (an autocrine effect), and these terms are distinguished from the long-distance endocrine effects of hormones.
• Many of the chemicals that regulate inflammation and immunity are in a class called cytokines, which are small proteins that serve as a chemical communication network among immune cells.
• Damaged tissues release cytokines that stimulate the red bone marrow to release neutrophils into circulation, raising the blood neutrophil count within hours.
• Inflammation involves three major processes: mobilization of the body’s defenses, containment and destruction of pathogens, and tissue cleanup and repair.
• Cytokines include interferons, interleukins, tumor necrosis factor, chemotactic factors, and other chemicals that will be encountered in this discussion.
• Inflammation is mediated by several types of cells and chemicals summarized in table 21.1.
• Humoral Immunity
• The genome contains several hundred DNA segments that are shuffled and combined in various ways to produce antibody genes unique to each clone of B cells, a process called somatic recombination.
• These and other mechanisms explain how we can produce such a tremendous variety of antibodies with a limited number of genes.
• The life history of a T cell involves three stages and three anatomical stations in the body.
• Somatic hypermutation not only recombines preexisting DNA but creates wholly new DNA sequences.
• The major cells of the adaptive immune system are lymphocytes, macrophages, and dendritic cells, which are especially concentrated at strategic places such as the lymphatic organs, skin, and mucous membranes.
• T lymphocytes, also known as T cells, are the principal agents of adaptive immunity.
• The genome also contains several hundred DNA segments that are shuffled and combined in various ways to produce T cell receptor genes unique to each clone of T cells, a process called somatic hypermutation.
• NK cells are involved in innate immunity.
• Each person has a much smaller subset of these, but such an enormous potential helps to explain why we can deal with the tremendous diversity of antigens that exist in our environment.
• Lymphocytes fall into three classes: natural killer (NK) cells, T lymphocytes, and B lymphocytes.
• Somatic recombination forms new combinations of DNA base sequences in somatic (nonreproductive) cells.
• When a person is first exposed to a particular antigen, the humoral immune reaction is called the primary response.
• Complement fixation is an action in which antibodies bind complement proteins to an enemy cell, leading to its destruction.
• The appearance of protective antibodies is delayed in the primary response.
• The first time a person is exposed to a particular antigen, their plasma cells produce mainly an antibody class called IgM.