Occasionally, the immune reacts against self antigens. In this case, B cells may be stimulated to make antibodies against normal parts of the body. Th and Tc cells also participate in autoimmune reactions. Autoimmune reactions are unfortunate mistakes of the immune system. 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.