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Biology

Chapter 24: 1-11

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Lecture

Immunity: Immune System Overview

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How the Immune System Works

The immune system includes all tissues, organs, and organ systems that provide defenses against invading biological cells, like viruses and bacteria. These systems can be non-specific, in which case they responde to any "invasion" stimulus or situation, like broken skin, or they can be cells or cell products targeted to attack only one kind of invader.

In this lecture, we concentrate on identifying all the pieces in the system. In the next web lecture, we'll look at the overall processes through which these immune system components protect our own body cells from infection or destruction by non-self cells and their products.

The Immune System Components

Non-Specific Response Immune System (Innate) Components
Component Location Defense activity
Skin Body surfaces Physical barrier, acid (low pH and lysosomic sweat, tears, saliva, and other gland excretions)
Mucous membranes Respiratory and digestive system linings. Physical barrier (hair, sticky fluid traps particles)
Phagocytic cells Carried in blood; act in interstitial fluid, body tissues
Neutrophils (60% of white blood cells, short-lived, diffuse into tissue.).
Small leukocytes; triggered by antigens to leave blood system and release lysosomic enzymes; can kill up to 20 bacteria
Macrophages (large, long-lived, develop in tissues of organs from monocytes that move from blood to tissue when infection occurs.
Release cytokines; ingest foreign cells and damaged/dead self-cells; can kill up to 100 bacteria
Eosinophils (similar to macrophages, less active)
Attach to and immobilize parasites
Natural killer cells (lymphocytes)
Release enzymes to damage foreign cell membranes; produce cytokines to control T-cell and B-cell functions. Similar to T-cells, but non-specific.
Antimicrobial Proteins Carried in blood; act in interstitial fluid, body tissues
Cytokines
Interferons stimulate proteins to repress viral reproduction, destroy tumors; interleukins trigger fever response; tumor necrosis factors kill tumor cells.
Complement system proteins
Proteins that act in sequence, each stimulating another through a chain of reactions to stimulate histamine release, attach to antigens and attract macrophages, or even directly destroy antigens.
Inflammatory Response Body tissues near invasion site
Histamines (released by basophil leukocytes)
Attract neutrophils and macrophages, dilate blood vessels, cause swelling and temperature increase
Clotting agents
close off broken blood vessels
Lymphatic System Lymph nodes, vessels; glands (thymus, tonsils, appendix, adenoids, spleen, bone marrow)
Lymph
Carries immune system agents to infected tissues; carries destroyed cells and wastes away
Nodes
Storage areas for B and T cells, macrophages
Specific Response Immune System Components
antigen
Any molecule that triggers an immune response
antibody
Molecule produced by body to attach to antigen and mitigate effects
passive immunity
Antibodies transferred from another (mother to fetus)
acquired immunity
Antibodies stimulated by exposure to antigen through infection or vaccination
Lymphatic System Lymph nodes, vessels; glands (thymus, tonsils, appendix, adenoids, spleen, bone marrow)
Lymph
Carries immune system agents to infected tissues; carries destroyed cells and wastes away
Nodes
Storage areas for B and T cells, macrophages
Humoral Immunity Mature in bond marrow; release antigens in blood or interstitial fluids
B-Cells → plasma cells
Secrete antibodies
Cell-mediated Immunity Mature in thymus gland; stimulate B-cell and phagocyte activities of other cells in blood; attack antigens within body cells
Cytoxic T-Cells
Killer T cells: destroy cells with foreign antigens: virus-infected cells, cancer cells, foreign tissue grafts
Supressor T cells
Release cytokines to inhibit T-cell/B-cell activity
Helper T-cells (CD4 cells)
Secrete cytokines that active immune system responses
Antibodies (immunoglobulins) Secreted by B-cells in the lymph nodes, they pass into the blood for deployment to the infected area, where they fuse to antigens and tag them for destruction by B-cell and T-cell agents
IgG
Gamma globulins in blood; attack bacteria, viruses, some fungi.
IgM
Like IgG, found in blood, and attack bacteria, viruses, some fungi.
IgA
Found in mucous: attack inhaled/ingested pathogens.
IgD
Binds to antigen; activates B-cell response.
IgE
Binds to antigen, activates histamine release.

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