One of the important side effects of immunity, is the development under some conditions, of allergies.
There are several different types of allergy, some of which can occur in any person, others that occur only in persons who have a specific allergy tendency.
An allergy that occurs in normal people "delayed-reaction allergy" frequently causes skin eruptions in response to certain drugs or chemicals, particularly some cosmetics and household chemicals. Delayed-reaction allergy is caused by activated T cells and not by anti-bodies.
This type of allergy is usually triggered by repeated exposure to a particular product or products. Although the toxin itself does not cause much harm to the tissue, it causes the formation of activated T cells. Continued exposure to the toxin, diffuses the activated T cells in sufficient numbers into the skin to combine with the toxin and elicit the cell mediated type of immune reaction and because of this delayed reaction one can build up a massive allergic effect which in occasions can result in serious tissue damage.
Some people have an "allergic tendency". Their allergies are called atopic allergies, because they are caused by a non ordinary response of the immune system. The allergic
tendency is characterised by the presence of large quantities of IgE antibodies, these antibodies are called reagents or sensitising antibodies to distinguish them from the more common IgG antibodies.
When an allergen (defined as an antigen that reacts specifically with a specific type of IgE reagin antibody) enters the body, an allergen- reagin reaction takes place, and a subsequent allergic reaction then follows. The allergic reaction can then cause havoc in the body releasing immediately or secreted shortly there after histamine, slow-reacting substance of anaphylaxis, eosinophil chemotactic substance, a protease, a neutrophil chemotactic substance,
heparin, and platelet activating factors.
These substances cause such phenomena as dilation of the local blood vessels, attraction of eosinophils and neutrophils
to the reactive site, damage to the local tissue by the
protease, increased permeability of the capillaries and loss of
fluid into the tissue, and contraction of smooth muscle cells.
Therefore, any number of different types of abnormal tissue
responses can occur. Some examples of allergic reactions caused in this manner are;
