The Adaptive Immune Response Chapter 16 The Adaptive Immune Response

Introduction The innate immune system is always ready to respond to a pattern that represents damage or invasion. The adaptive immune system matures throughout life, developing an effective response for specific invaders that it has encountered. An important hallmark of this system is memory.

The adaptive system has molecular specificity. This means that it protects a person from measles if they have had them before, but that defense is different from that for the chickenpox. It can also distinguish “self” from “dangerous” This serves to keep the system from attacking our cells all of the time.

16.1 Strategy of the Adaptive Immune Response Our first exposure to a given microbe or antigen, systemic evidence of the adaptive response takes a week of more to develop. The first response is called the primary response, and as a result of this encounter, the body is able to “remember” the mechanism that was effective against the microbe.

When there is another encounter with the same microbe, an enhanced antigen specific response is created. This is called the secondary or anamnestic response.

The adaptive system uses two basic strategies for encountering foreign material: Humoral immunity – works to eliminate antigens that are extracellular, like those found in blood or fluids around tissues Cell-mediated immunity – antigens residing within a host cell, such as a virus.

Overview of Humoral Immunity It is mediated by B cells, which originate in the bone marrow of humans. B cells are triggered to proliferate and differentiate to form plasma cells, which produce antibodies Some B cells will form memory cells, which are long-lived B cells that can respond quickly if an antigen is encountered again

Antibodies have two functional regions: the two stems and stem of the molecule. The arms bind to a specific antigen, while the stem functions to alert other components of the immune system to eliminate the bound molecule.

Overview of Cellular Immunity Cell-mediated immunity is regulated by T cells, which mature in the thymus. There are two subsets of T cells: cytotoxic and helper. T cells will not activate until receiving a signal confirming that the antigen is a threat; this signal comes from a dendritic cell.

16.2 Anatomy of the Lymphoid System Lymphoid system is a collection of tissues and organs designed and located to bring the B and T cells into contact with any antigens that enter the body. Lymphatic vessels carry the fluid, lymph, which bathes the body tissues. If inflammation is present, the lymph accumulates.

Primary Lymphoid Organs Bone marrow and thymus, where hematopoietic stem cells designed to become B and T cells are found. Once the cells mature, they migrate into the secondary organs to await antigens.

Secondary Lymphoid Organs Sites where lymphocytes gather to contact various antigens that have entered the body. They include lymph nodes, spleen, tonsils, adenoids, and appendix. Their purpose is to capture antigens and bring them in to contact with lymphocytes.

16.3 The Nature of Antigens The term antigen comes from the compounds that elicit the production of antibodies. Comes from the combination of antibody generator. When referring specifically to an antigen that elicits an immune response in a given situation, it is termed an immunogen.

16.4 The Nature of Antibodies Antibodies are immunoglobulins are Y-shaped proteins, with two arms and a stem region. The two identical arms are called Fab regions, and they bind antigens. The stem, Fc region, enlists other components of the immune system.

Protective Outcomes of Antibody-Antigen Binding Neutralization – antibodies bind and coat toxins or viruses to prevent them from interacting with a cell. Immobilization and prevention of adherence – binding of an antibody to cilia or flagella to prevent motility. Agglutination and precipitation – binding of multiple antigens to create one large group for phagocytosis.

Opsonization – facilitate the attachment of a phagocytic cell as a prelude to engulfment. Complement System Activation – binding of antigen to antibody to activate the complement system.

IgG Antibodies Monomer 80% of serum Abs Fix complement In blood, lymph, and intestine Cross placenta Enhance phagocytosis; neutralize toxins and viruses; protects fetus and newborn Half-life = 23 days

IgA Antibodies Dimer 10–15% of serum Abs In secretions Mucosal protection Half-life = 6 days

IgM Antibodies Pentamer 5–10% of serum Abs Fix complement In blood, in lymph, and on B cells Agglutinates microbes; first Ab produced in response to infection Half-life = 5 days

IgE Antibodies Monomer 0.002% of serum Abs On mast cells, on basophils, and in blood Allergic reactions; lysis of parasitic worms Half-life = 2 days

IgD Antibodies Monomer 0.2% of serum Abs In blood, in lymph, and on B cells On B cells, initiate immune response Half-life = 3 days

Works Cited Nester, Anderson, Roberts and Nester. Microbiology: A Human Perspective. Tortora, Funke, and Case. Microbiology: An Introduction.