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The Immune System

containing disabled or killed pathogens. The body does require prior exposure to an antigen to develop
an active immunity. Some parents expose their children to some antigens so they will have immunity to
these diseases later in life.

Passive Immunity occurs when we acquire antibodies made by another human or animal. Passive
immunity is passive because it requires no response from the person's immune system. In passive
immunity you are not presenting the body with foreign antigens. Therefore your immune system will
not need to use B cells, and we know that if the B cells are never introduced your body isn't making
antibodies and it isn't making memory B cells. The transfer of antibodies from mother to fetus across
the placenta is one example. Injections containing antibodies are another. Sometimes travelers going
abroad may be injected with gamma globulin, but this passive immunity last only about three months.
Passive immunizations are used to protect people who have been exposed to infections or toxins, like
snake venom or tetanus.

ALLERGIC RESPONSES/INFLAMMATORY RESPONSES

An allergy is an inflammatory immune response to a nonpathogenic antigen. Left alone, the
antigen is not harmful to the body, but if someone is sensitive to the antigen, the body produces an
inflammatory response designed to get rid of it. Allergic inflammatory responses can range from from
mild tissue damage to fatal reactions. The immune response in allergies is called sensitivity or
hypersensitivity to the antigen. Immediate hypersensitivity reactions are mediated (immune
destruction) by antibodies and occur within minutes of exposure to antigens, which are called allergens.
Delayed hypersensitivity reactions are mediated by helper T cells and macrophages and may take
several days to develop.

What happens during a immediate hypersensitivity reaction?

1-Foreign protein or antigen is introduced
2-Macrophage cell ingests (phagpcytosis)
3- Activation of Th lymphocyte
4-Th (helper) lymphocyte
5-Foreign protein bound by membrane antibodies
6-B lymphocyte
7-Antigen processing (MHC II type)
8-Antigen-MHC II complex (antigen presentation)
9-Production of antigen-specific antibodies
10-Activation of B lymphocyte with active Th

2. Upon reexposure, the body reacts more strongly and rapidly. The allergen binds to IgE already
present on mast cells, triggering the immediate release of histamine, cytokines, and other mediators that
cause allergic symptoms. The severity of the reaction varies, ranging from localized reactions near the
site of where the allergen entered, such as a rash. To the most severe allergic reaction called
anaphylaxis. In an anaphylactic reaction, massive release of histamine and other cytokines cause
widespread vasodilation, circulatory collapse, and severe bronchoconstriction. Unless treated promptly,
anaphylaxis can result in death.

Skin tests for allergies of certain allergens can be injected into the skin. This is a good way to find
out what one might be allergic to so they can eliminate further exposure. Allergens that can cause

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