Hypersensitivity Reactions: Types, Causes and Treatment

What Is Hypersensitivity?

The immune response protects the body from damage. Immunity fights off invasive and infectious substances. Sometimes, the immune system yields some undesirable responses. For example, the immune system identifies harmless substances as harmful. Such responses are called hypersensitivity responses.

An antigen or allergen is a toxic or foreign substance that leads to an immune reaction. Recognition of an antigen to be a potential threat, the immune system shows an immune response to get rid of it. The body can produce various types of hypersensitivity reactions. These reactions vary according to the antigen it is exposed to and the body's response to it.

What Are the Different Hypersensitivity Reactions?

A hypersensitivity reaction is a hyperimmune response to an antigen. Each type of reaction is different depending on the antigen the body recognizes, the type of immune response the body generates, and the time required for the body to produce the answer.

Hypersensitivity reactions are referred to as allergies, a form of hypersensitivity. An allergic reaction involves signs and symptoms experienced, while a hypersensitivity reaction is an immunological process in the body. There are four types of hypersensitivity reactions.

Type 1 Hypersensitivity Reaction.

• Type 1 hypersensitivity causes an immediate response. This reaction occurs post-exposure to an antigen. The body responds to an antigen in type I reactions by producing an IgE antibody.

• Different factors trigger type 1 hypersensitivity responses; these include antigens from:

  • Food like nuts, shellfish, and soy.

  • Animal-related agents are derived from cats, rats, or bee stings.

  • Environmental agents like mold, latex, and dust.

  • Allergic reactions to allergic rhinitis, asthma, and conjunctivitis.

• Stages of type 1 hypersensitivity:

  • Sensitization - During the sensitization stage, the person comes in contact with the antigen but has no symptoms.

  • Effect - In the effect stage, the person has second exposure to the antigen. As the body recognizes the antigen a second time, it produces a response and causes the symptoms typically experienced with an allergic reaction.

• Symptoms of type 1 hypersensitivity are as follows:

  • Rash.

  • Flushing.

  • Hives.

  • Itching.

  • Edema.

  • Wheezing.

  • Rhinitis.

  • Stomach cramps.

  • Nausea and vomiting.

  • Shortness of breath.

  • Cardiac symptoms.

  • Loss of consciousness.

• Diagnosing type 1 hypersensitivity includes assessing the personal history, signs, and symptoms and evaluating the medical records. This is followed by physical examination and blood and allergy tests to identify the antigen causing the reaction.

• Treatment options for type 1 hypersensitivity, according to the cause of the reaction and body response, are as follows. Some may require emergency medical care immediately, and people with mild symptoms need medications. Exposure to allergens should be avoided in the future.

• Some treatment options are as follows.

  • Adrenaline or Epinephrine.

  • Systemic glucocorticoids.

  • Antihistamines.

Type 2 Hypersensitivity Reaction.

Just like type 1 reactions, type 2 hypersensitivity reactions also require antibodies. Type 2 and type 3 hypersensitivity occurs due to the same class of antibody called IgG. The difference between them is the variety of antigens that produce a response. Also, type 2 reactions involve IgM antibodies. Type 2 hypersensitivity can cause cytotoxic reactions. In these reactions, healthy cell death occurs as they react to the antigens. This causes long-term damage to cells and tissues, driving conditions like.

• The blood disorder - thrombocytopenia occurs due to inadequate platelets.

• Autoimmune hemolytic anemia is due to the bursting of red blood cells.

• Autoimmune neutropenia due to the destruction of neutrophils.

• Autoimmune conditions like Graves’ disease.

Common causes of type 2 hypersensitivity reactions are:

• Penicillin.

• Thiazides.

• Cephalosporins.

• Methyldopa.

According to the trigger and the response, there are different groups of type 2 hypersensitivity. Diagnosis differs according to these groups, as a physician has to be careful and avoid further damage triggering. Diagnosis involves direct immunofluorescence to identify the causative antibodies. Treatment for type 2 hypersensitivity involves using immunosuppressants to prevent antibodies' unusual response. Treatment options include the following:

• Systemic glucocorticoids.

• Cyclophosphamide.

• Cyclosporin.

• Intravenous immunoglobulin infusions.

• Plasmapheresis.

Type 3 Hypersensitivity reaction

Type 3 hypersensitivity reactions involve antigens and antibodies forming complexes in the skin, blood vessels, joints, and kidneys. These complexes lead to a series of responses that cause tissue damage.

The causes of a type 3 hypersensitivity reaction are as follows.

• Drugs with proteins from organisms, such as antivenins.

• The drug Infliximab for autoimmune conditions.

• Animal-derived things like insect stings or tick bites.

Type 3 hypersensitivity reactions can cause the following.

• Serum sickness.

• Lupus rheumatoid arthritis.

• Small-vessel vasculitis.

• Henoch-Schönlein purpura.

• Diagnosing type 3 hypersensitivity needs clinical history, a physical exam, and various assessments, like blood and urine test, biopsies, and imaging scans.

• Depending on the severity and type of hypersensitivity response the treatmntoptions are available. First, however, treatment is required to control the underlying conditions. This involves immunosuppression with systemic glucocorticoids and disease-modifying drugs.

Type 4 Hypersensitivity Reaction.

Type 4 hypersensitivity reactions are cell-mediated. Antibodies are not involved in these reactions. Instead, white blood cells called T cells regulate type 4 hypersensitivity reactions.

Type 4 hypersensitivity is further divided into type 4a, type 4b, type 4c, and type 4d, according to the type of T cell involved and its reaction. This type is different from the other type of reactions, and it causes a delayed response. The three types of type 4 hypersensitivity are as follows:

• Contact dermatitis.

• Tuberculin-type hypersensitivity.

• Granulomatous-type hypersensitivity.

Common causes of type 4 hypersensitivity reactions are exposure to poison ivy, metals, and drugs like antibiotics or anticonvulsants. Diagnosing contact dermatitis is done using a skin biopsy and skin patch tests. In addition, a doctor can order a chest X-ray while diagnosing tuberculin-type hypersensitivity. Granulomatous-type hypersensitivity is challenging to diagnose, and any of the following can be used for the assessment:

• X-ray.

• Lymph node biopsy.

• Enzyme analysis.

• Salivary gland analysis.

Treatment depends on the outcome. For example, contact dermatitis needs the application of topical steroids. Treatment for granulomatous-type hypersensitivity also involves steroid therapy, and treatments vary according to the outcome of the reaction. Methotrexate can be prescribed as steroid treatment in a patient with pulmonary sarcoidosis. Tuberculin-type hypersensitivity requires a standard procedure for tuberculosis. Common treatments for tuberculin-type hypersensitivity include:

• Rifampin.

• Isoniazid.

• Pyrazinamide.

• Ethambutol.

Type 5 Hypersensitivity Reaction

Type 5 hypersensitivity reactions occur when an antibody targets receptors on a cell that a hormone would ordinarily activate. Although additional research is needed, some experts believe that this reaction is a subset of type 2 rather than a separate kind.

Nonallergy Hypersensitivity Reaction.

Hypersensitivity reactions are allergic reactions. Some show a non-immune anaphylactic reaction to some drugs or foods. These reactions cannot be distinguished from allergic reactions. They cause direct symptoms without the involvement of antibodies or T cells.

Conclusion:

The diagnosis of hypersensitivity or non-allergic reactions depends on various elements like allergological and laboratory tests and clinical reports. The importance of allergy testing investigation with a suspected reaction to a substance and the severity of the signs and symptoms to prevent exposure to the same substance to avoid severe adverse reactions.