For unknown reasons, women are more likely to suffer from autoimmunity than men. Some people have deficient immune responses. These people have more severe and more frequent infections. Immunodeficiency may arise from an inherited condition or it may be acquired after birth. Due to genetic defects in macrophages, neutrophils, T cells or B cells.
Allergies are immune responses against non-infectious agents.
Antigens that cause allergic reactions are called allergens. When an allergic person is exposed to an allergen, they make a kind of antibody called IgE. IgE is different from other antibodies because it can bind to allergens and to surface of mast cells and basophils. During second or subsequent exposures to the allergen, the allergen binds to IgE that is on the surface of the mast cells and basophils and causes them to degranulate, releasing histamine and other mediators of inflammation. These substances cause the symptoms of allergy, namely, increased mucus secretion, constriction of the airways, watering eyes, sneezing, increased vasodilation and permeability leading to swelling. Each time the allergic person is exposed to the allergen, the allergic reaction gets a little worse.