Antigens: foreign substances (e.g., bacteria or viruses) in the body that are capable of causing disease. The presence of antigens in the body triggers an immune response, usually the production of antibodies.1

Arthritis: inflammation of joints due to infectious, metabolic, or constitutional causes.2

Asperger syndrome: a developmental disorder resembling autism that is characterized by impaired social interaction, by repetitive patterns of behavior and restricted interests, by normal language and cognitive development, and often by above-average performance in a narrow field against a general background of deficient functioning—also called Asperger’s disorder.2

Asthma: a disorder that causes the airways of the lungs to swell and narrow, leading to wheezing, shortness of breath, chest tightness, and coughing.3

Atopy: a genetic disposition to develop an allergic reaction (as allergic rhinitis, asthma, or atopic dermatitis) and produce elevated levels of IgE upon exposure to an environmental antigen and especially one inhaled or ingested.2

Attention deficit disorder (ADD): a syndrome of disordered learning and disruptive behavior that is not caused by any serious underlying physical or mental disorder and that has several subtypes characterized primarily by symptoms of inattentiveness or primarily by symptoms of hyperactivity and impulsive behavior (as in speaking out of turn) or by the significant expression of all three.2

Attenuated vaccine: a vaccine in which live virus is weakened through chemical or physical processes in order to produce an immune response without causing the severe effects of the disease. Attenuated vaccines currently licensed in the United States include measles, mumps, rubella, polio, yellow fever, and varicella. Also known as a live vaccine.1

Autism: a developmental disorder that appears in the first 3 years of life, and affects the brain’s normal development of social and communication skills.3

Autoimmune Diseases Disorder: a condition that occurs when the immune system mistakenly attacks and destroys healthy body tissue. There are more than 80 different types of autoimmune disorders.3



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