Immune System

The Immune System The function of the immune system is to fight infection through the production of cells that inactivate foreign substances or cells This process is called immunity

First Line of Defense The function of the first line of defense is to keep pathogens out of the body. This role is carried out by skin, mucus, sweat, and tears. Your body’s most important non-specific defense is the skin Mucus, saliva, and tears contain lysozyme. Lysozyme breaks down the cell wall of many bacteria.

Second line of defense If pathogens do enter your body, they may replicate rapidly and release toxins. When this happens, the inflammatory response is activated, The inflammatory response is a non-specific response to tissue damage caused by injury or infection.

The Inflammatory Response When pathogen are detected, the immune system produces millions of white blood cells – lymphocytes, which fight the infection Blood vessels near the wound expand to allow more white blood cells to enter the tissues.

Fever The immune system also releases chemicals that increase the core temperature of the body. A fever is advantageous because many pathogens can only survive within a narrow temperature range.

Interferons When viruses enter cells, sometimes the cell will produce a chemical called interferon – because it interferes with viral replication. This gives the specific immune response more time respond.

Specific Defenses A substance that gets past the non-specific defenses, will trigger an immune response. A substance that triggers an immune response is called an antigen.

Specific Immune Defences The cells of the immune system that recognize specific antigens are two types of lymphocytes (white blood cells) B lymphocytes (B cells) and T lymphocytes (T cells) B cells provide immunity in the body fluids (humoral immunity) T cells provide a defense against abnormal cells and pathogens in side cells. (cell-mediated immunity).

Humoral Immunity When a pathogen invades the body, its antigens are recognized by a small fraction of the body’s B cells. These B cells grow and divide rapidly producing plasma and memory cells Plasma cells release antibodies. Memory cells remain in the body long after the antibodies have neutralized the infection.

Antibody

Cell-Mediated Immunity The body’s primary defense against its own cells when they have become cancerous or infected by a virus is called cell-medicated immunity.

Cell-Mediated Immunity During cell-mediated immunity, T cells divide and differenciate into killer T cells, helper T cells, suppressor T cells, and memory T cells. Killer T cells track-down and destroy the bacteria, fungi, protozoan, or foreign tissue that cantains the antigen. Helper T cells make memory T cells for future attack by same pathogen. Suppressor T cells release chemicals that shutdown killer T cells.

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