Biology 12

128 MHR • Unit 2 Homeostasis

characterizes this disease. The solution to the

problem of immediate allergic reactions shown

in Figure 4.20 may be somewhat extreme.

Delayed allergic responses are set off by T cells

that have been sensitized by previous contact with

the allergen. In these cases, the reaction is slower

and lasts for a longer period of time. Allergic

reactions to certain cosmetics and jewellery are

examples of this type of allergy.

Food allergies are becoming an increasing

problem in Canada. Why have they become a major

health issue? Is it due to better diagnosis, more food

additives, or other unknown environmental causes?

The answer is not clear yet, but we know that more

people are becoming sensitized to foods that have

been part of the human diet for thousands of years.

Students and teachers in many schools now have

Figure 4.20Asthma attacks and the allergic reaction known

as hay fever can have many triggers, one of which is the

pollen of a variety of plants. These croquet players have

found a unique solution to the problem.

Figure 4.19Antibody immunity uses B cells and antibodies to defend your body

against invading pathogens.

Bacteria invade the body, and the

body reacts to these antigens.

Macrophages ingest the antigens,

break them down, and present

pieces of them on their surfaces.

T cells have receptor sites that

recognize and bind to the antigens

presented on the macrophages.

T cells become activated and release

chemicals that affect B cells.

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