Recognizing the Four Types of Hypersensitive Reactions

Your immune system protects you from diseases, viruses and infections. However, sometimes it mistakes a harmless substance, like pollen at The Philadelphia Flower Market for a dangerous intruder and overreacts. This type of response is known as a hypersensitive reaction, of which there are four. We review how to recognize the four types of hypersensitive reactions below.

Type 1

A type 1 hypersensitive reaction causes an immediate response following exposure to an antigen and involves the production of the antibody Immunoglobulin E.

Type 1 reactions take place in two stages: the sensitization stage, when the antigen is first encountered, and the effect stage, when symptoms present. Symptoms of a type 1 reaction include:

• Rash
• Flushing
• Hives
• Itching
• Edema
• Wheezing
• Rhinitis
• Stomach cramps
• Nausea
• Vomiting
• Shortness of breath
• Cardiac symptoms
• Loss of consciousness

This type of reaction can be triggered by:

• Food products like nuts, shellfish and soy.
• Animal sources like cats and bee stings.
• Environmental sources like mold, dust and latex.
• Allergic conditions like allergic rhinitis, allergic asthma and conjunctivitis.

Type 2

A type 2 reaction involves the production of the antibodies Immunoglobulin G and Immunoglobulin M. This type of reaction can by cytotoxic, which means that healthy cells die as they respond to antigens. This can result in:

• Immune thrombocytopenia, a blood disorder
• Autoimmune hemolytic anemia
• Autoimmune neutropenia
• Grave’s disease

Type 2 reactions can be caused by:

• Penicillin
• Thiazides
• Cephalosporins
• Methyldopa

There is a subtype of type 2 reactions, known as a type 5 reaction. This type of reaction occurs when an antibody targets receptors on a cell that a hormone would normally activate.

Type 3

A type 3 reaction entails antigens and antibodies forming complexes in the skin, blood vessels, joints and kidney tissues. This ultimately can result in tissue damage as well as:

• Serum sickness.
• Rheumatoid arthritis.
• Small vessel vasculitis.
• Henoch-Schönlein purpura.

Type 3 reactions may be caused by:

• Drugs containing proteins from other organisms, like antivenins.
• Infliximab, a drug used to manage autoimmune conditions.
• Animal sources like tick bites and insect stings.

Type 4

A type 4 hypersensitive reaction differs from the others in that the reactions are cell-mediated, meaning white blood cells known as T cells control the reaction rather than antibodies. This type of reaction also differs in that it is a delayed reaction rather than immediate.

The three ways a type 4 reaction can present are:

• Contact dermatitis
• Tuberculin-type hypersensitivity
• Granulomatous-type hypersensitivity

These can be caused by:

• Poison ivy
• Certain metals
• Antibiotics
• Anticonvulsants

For more information or to schedule an appointment for an allergy test, call Pinnacle ENT Associates today.