The Immune System

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Antibodies to nonself blood types exist in the body.

Transfusion with incompatible blood leads to destruction of the transfused cells.

Recipient-donor combinations can be fatal or safe.

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Disruption in immune system function can elicit or exacerbate disease

Some pathogens have evolved to diminish the effectiveness of host immune responses.

If the delicate balance of the immune system is disrupted, effects range from minor to often fatal.

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Allergies

Allergies are exaggerated (hypersensitive) responses to antigens called allergens.

In localized allergies such as hay fever, IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells.

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Mast cells, IgE, and the allergic response

Allergen

IgE

Granule

Mast cell

Histamine

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The next time the allergen enters the body, it binds to mast cell–associated IgE molecules.

Mast cells release histamine and other mediators that cause vascular changes leading to typical allergy symptoms.

An acute allergic response can lead to anaphylactic shock, a life-threatening reaction that can occur within seconds of allergen exposure.

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Autoimmune Diseases

In individuals with autoimmune diseases, the immune system loses tolerance for self and turns against certain molecules of the body.

Autoimmune diseases include systemic lupus erythematosus, rheumatoid arthritis, insulin-dependent diabetes mellitus, and multiple sclerosis.

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X-ray of a hand deformed by rheumatoid arthritis

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Exertion, Stress, and the Immune System

Moderate exercise improves immune system function.

Psychological stress has been shown to disrupt hormonal, nervous, and immune systems.

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Immunodeficiency Diseases

Inborn immunodeficiency results from hereditary or developmental defects that prevent proper functioning of innate, humoral, and/or cell-mediated defenses.

Acquired immunodeficiency results from exposure to chemical and biological agents.

Acquired immunodeficiency syndrome (AIDS) is caused by a virus.

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Acquired Immune System Evasion by Pathogens