10.2 The Immune Response Some macrophages float throughout the body…other stay in a fixed location The fixed macrophages are present in the spleen, lymph nodes and other lymphatic tissue

Complement Proteins 20 known types Inactive under normal conditions Activated by marker proteins from invading microbes  become messengers Immobilizes the invader A second group punctures the bacterial or fungal membrane A third group attaches to the invader

Lymphocytes Specialized white blood cells that produce antibodies Antigens: produces antibodies, present on the cell membranes and outer coats of viruses

T Cells Produced in bone marrow and store in the thymus gland T cells seek out intruders and signal an attack Some T cells identify the invader by it’s antigen markers

B Cells Multiply and produce antibodies Each B cell produces a single type of antibody, displayed on the cell membrane B cells are released from the bone marrow into the blood stream where some become plasma cells Tutorial 18.4 Humoral Immune Response

Antigen-Antibody Reactions AntibodiesAntibodies: Y-shaped proteins engineered to target specific foreign invaders Similar tails, with variations at the outer edge of each arm

Antigen-Antibody Reactions Different antigen markers are located on the membrane of a virus or bacterium As antibodies attach to antigen, the complex gets larger Interaction of Antigen Presenting Cells and T-helper Cells

Receptor sites Found on different cells…toxins can affect different specific areas of the body The receptor site accepts a specific hormone or nutrient with a lock and key method Antibodies block toxins by binding the receptor sites The Rockefeller University - The Body's Guard

Viruses Also use receptor sites to enter cells DNA is injected into the cell, and the protein coat is left bound to it’s specific receptor Different viruses are specialized

HIV Attaches to the receptor sites of the T cell The T cell engulfs the virus, but it’s protein coat is still attached to the receptor site The protein coat blocks the receptor site that normally binds invasive antigens Why is this a problem?

Antibodies Antibodies bind to viruses, changing their shape so that the virus cannot bind the receptor sites A mutation will occasionally change the shape of the viral protein coat

Recognition of Antigens Fig 7, pp. 469 When a macrophage engulfs an invader, the antigen markers are pushed to it’s membrane Helper T cells read the antigen’s markers and release lymphokine Helper T cells later trigger B cells B cells form clones Animations Animation: The Immune Response

Killer T Cells Puncture cell membranes of intruders Kills body cells infected with viruses preventing the virus form reproducing Destroys mutated cells…cancer? Organ transplant rejection?

Suppresor T Cells Signal immune system to shut down Most B and T cells die off a few days after the infection is gone, but some remain for a long time after for protection Memory B cells

Immune System Memory Immunity is based on maintaining an adequate number of anitbodies Memory B Cell: Generated during an infection, holds a blueprint of the antigen or antigens that characterize the invader

Matching Tissues for Organ Transplant The donor organ is usually identified as an invader by the protein markers on it’s cell membrane The recipient makes antibodies to destroy the foreign invader Humoral Immunity: Introduction