THE IMMUNE RESPONSE BIO11 This lesson meets the following DoE Specific Curriculum Outcomes for Biology 11: 116-7

THE IMMUNE RESPONSE The first line of defense: Skin and mucous membranes provide physical barriers that prevent most infectious organisms from entering the body. The second line of defense: non- specific immune response by macrophages (a type of leukocyte) destroy microbes by phagocytosis and inflammatory response.

MACROPHAGES Two responsibilities: 1.They release a chemical that causes blood vessels to dilate, increasing blood flow and temperature at the site of the infection. The heightened temp may be enough to destroy the invader. 2.They seek out and destroy foreign invaders through phagocytosis. The antigens of the invader are not destroyed but are pushed toward the cell membrane of the macrophage.

IMMUNE RESPONSE cont. The third line of defense: The specific immune system. This includes a variety of cells that recognize foreign substances and act to neutralize or destroy them. Lymphocytes are the primary components of this system.

LYMPHOCYTES Cells hat produce antibodies (proteins that protect the body from invaders by reacting with the antigens on the invader’s cell membrane). Our immune system has two different types of lymphocytes: T cells and B cells.

T CELLS Produced in the bone marrow and stored in the thymus gland. These cells act as sentries or guards for the immune system - its mission is to seek out the intruder and signal the attack. Some T cells identify the invader by its antigen markers. Once the antigen is identified, another T cell passes this information on to the antibody- producing B cell.

B CELLS Both produced and mature in the bone marrow. These cells are responsible for the production of antibodies and memory cells.

HELPER T CELLS Circulate in the blood plasma looking for the antigens of foreign invaders that have been engulfed by macrophages. Once an invader is detected, the helper T cell sends a chemical message to the B cell which produces the appropriate antibody.

ANTIBODY RESPOSE The antibody is released into the body to search for the invader. Once found, the antibody attaches itself to the invader’s antigen, thereby disabling invaders. The antigen-antibody complex is then engulfed and destroyed by a macrophage.

KILLER T CELLS Helper T cells also activate an additional defender, the killer T cells, which search for intruders and disable it by puncturing its cell membrane. The true value of these cells is seen with viruses, which hide within a familiar host cell. The killer T cell attacks the infected cell, preventing the virus from reproducing.

SUPPRESSOR T CELLS Once the entire battle with the foreign invader has been won, these cells signal the immune system to shut down. Helper T cells and memory B cells, made by the B cells, remain in the blood, ready to trigger another immune response if the body is infected with the same pathogen.

ACTIVE VS. PASSIVE Immunity can be provided in two ways: 1.Passive immunity: memory cells are made to recognize a previous infection or when an individual receives antibodies from another person to combat disease (during pregnancy). 2.Active immunity: done through medical intervention and vaccines that may be induced in healthy people so that they can avoid becoming ill later (flu vaccine).

PASSIVE IMMUNITY DURING PREGNANCY Antibodies from the mother’s system cross the placental barrier during pregnancy and during breast feeding. This give the newborn short-term immunity to some diseases.