Hypersensitivity Reactions: Types & Mechanisms

Hypersensitivity Reactions

• Immune system's protective function can cause harm through exaggerated responses, known as hypersensitivity reactions.
• Gell and Coombs created a classification system in 1963, categorizing hypersensitivity reactions into types I, II, III, and IV based on tissue injury mechanisms.

Type I Hypersensitivity Reactions

• Histamine and other mediators are released from mast cells and basophils are involved.
• Allergic rhinitis, asthma, anaphylaxis, eczema, angioedema, conjunctivitis, gastroenteritis, and urticaria can ensue.
• Symptoms can range from mild to severe and life-threatening.
• Anaphylactic reaction: immediate response to a specific antigen after prior exposure (sensitization).
• During initial exposure, the immune system creates immunoglobulin E (IgE) antibodies that attach to mast cells.
• Later exposures cause the antigen to trigger mast cell release, leading to histamine release = vasodilatation, bronchoconstriction, mucus secretion, and vascular permeability.
• Localized exposure results in mild, local reactions. Systemic exposure leads to severe, widespread reactions.

Allergic Rhinitis

• Allergic rhinitis is the most common allergy.
• Perennial allergic rhinitis: Symptoms occur year-round.
• Hay fever: Symptoms occur seasonally; causative antigens are airborne.
• Pathophysiology: antigen-antibody reaction, decreases ciliary action, and increases mucus secretions, resulting in vasodilation and tissue edema.
• Signs and Symptoms: Sneezing, nasal itching, runny nose, itchy eyes, pale, cyanotic, edematous nasal mucosa, and allergic shiners (dark circles under eyes).
• Complications: sinusitis, nasal polyps, asthma, and chronic bronchitis from repeated allergic rhinitis episodes.
• Diagnostic tests: Identify offending allergens through skin testing (though not always reliable) or in-vitro allergy test (RAST) for IgE antibodies.
• Therapeutic measures: Remove environmental stimuli. Antihistamines and nasal decongestants relieve symptoms. Severe symptoms require corticosteroids, which can cause drying in older adults. Nasal congestion can be reduced through Intranasal saline irrigation, and rhinophototherapy is also effective. Immunotherapy is for severe symptoms until environmental antigen exposure no longer causes symptoms.

Atopic Dermatitis (Eczema)

• A familial, chronic inflammatory skin response.
• Pathophysiology: Allergic response mediated by IgE antibodies, or epithelial cell defect impairing skin barrier.
• Signs and symptoms: Pruritus, edema, dry skin, weeping lesions, crusting, scaling, and lichenification.
• Diagnostic tests: Diagnosis is based on clinical examination and exclusion of other conditions. Serum IgE levels are often elevated and correlate with disease severity. Cultures and sensitivity tests are needed if infection is suspected.
• Therapeutic measures: Treatment of itchiness, dryness, and inflammation. Use antipruritics, diluted bleach baths, cool soaks, sensitive skin soaps, oatmeal baths, moisturizers, emollients, topical corticosteroids, or topical calcineurin inhibitors. Infected lesions require topical or systemic antibiotics. Avoid triggers, control temperature and humidity for prevention.

Anaphylaxis

• Severe systemic type I hypersensitivity reaction.
• Causes: antibiotics (cephalosporins, penicillin, sulfonamides), anticonvulsants (phenytoin), NSAIDs (aspirin), foods (eggs, nuts, shellfish, wheat), latex, food additives (MSG, bisulfites), insect venom.
• Pathophysiology: IgE antibodies from previous sensitization attach to mast cells. Systemic exposure to the antigen releases histamine and other mediators. Respiratory/cardiac arrest can result, requiring immediate treatment.
• Signs and symptoms: Sudden life-threatening symptoms, generalized smooth muscle spasms (bronchial narrowing, stridor, wheezing, dyspnea, laryngeal edema, respiratory arrest), cramping, diarrhea, nausea, vomiting, increased capillary permeability (hypotension, tachycardia, increased respiratory symptoms), blood vessel dilation (decreased circulating volume, diffuse erythema, warmth), and neurologic changes.
• Diagnostic tests: Patient history, signs, symptoms, arterial blood gases (hypoxemia, hypercarbia, acidosis), ECG (arrhythmias). Allergen testing after recovery.
• Therapeutic measures: Immediate IM epinephrine; IV access for vasopressors and fluids; oxygen therapy. Tracheostomy/intubation with mechanical ventilation may be needed. Antihistamines and corticosteroids can be used.

Urticaria

• Type I hypersensitivity reaction.
• Causes: medicines, foods, chemicals, cold, stress, chronic conditions (lupus, lymphoma, hyperthyroidism, cancer).
• Pathophysiology: Antigen-stimulated IgE reaction, releasing mast cell contents (histamine).
• Signs and Symptoms: Raised, pruritic, non-tender, erythematous wheals on trunk and proximal extremities.
• Diagnosis: based on physical examination and history.
• Treatment: Depending on symptom severity. Epinephrine for severe cases, corticosteroids for inflammation, antihistamines to block histamine. Some cases require IgE monoclonal antibody therapy.

Angioedema

• Type I hypersensitivity reaction of varying causes.
• Allergic reaction is the most common cause, other causes are ACE inhibitors or idiopathic reasons. There are hereditary or acquired forms caused by C1 esterase inhibitor deficiency or dysfunction.
• Anxiety, infection, physical stimuli (cold, physical activity, surgery), or trauma can trigger angioedema.
• Pathophysiology: Temporary vascular permeability in submucosal and subcutaneous layers leads to swelling.
• Signs and symptoms: Localized swelling of skin, mucosa, or submucosa. Can occur with or without urticaria. Affects any part of the body or the face, eyes, and lips. Eruptions are nonpruritic and painless, but can lead to medical emergencies if upper airways are obstructed.
• Diagnosis: Comprehensive history and physical. Skin testing to find allergens.
• Therapeutic measures: Avoidance of antigens or allergen desensitization, Cinryze for prophylaxis, antihistamines, corticosteroids, Berinert for angioedema of the abdomen, face, or throat, Haegarda, Ecallantide, plasma kallikrein inhibitor, and icatibant to control symptoms. Fresh frozen plasma is used for angioedema symptoms associated with ACE inhibitor.

Nursing Considerations for Type I Hypersensitivity

• Assess patient symptoms, reporting sudden dyspnea, anxiety, restlessness, or chest/back pain. Identify allergies and reactions.
• Observe skin/lesions and include signs of infection. Note the patient's understanding of their condition, causes, treatment plan, and self-care practices.
• Nursing diagnoses: Impaired Gas Exchange related to laryngeal edema, Anxiety, or Deficient Knowledge.
• Monitor respiratory status, use of accessory muscles, changes in mentation, voice, or dysphagia. Elevate the patient if experiencing difficulty breathing.
• Stay with the patient to reduce anxiety, visualization techniques.
• Assess patient knowledge, discuss allergies and anaphylaxis, wearing a mask or vacuuming, administer epinephrine.
• Teach about signs of infection, cotton clothes and cool compresses and stress management.

Type II Hypersensitivity Reactions

• A cell or substance with an antigen attached to its cell membrane is destroyed.
• Immunoglobulin G (IgG) or immunoglobulin M (IgM) recognizes the antigen as foreign.
• Antibody attaches to the antigen, causing cell lysis or accelerated phagocytosis.
• Hemolytic transfusion reaction is an example

Hemolytic Transfusion Reaction

• Rare type II hypersensitivity due to ABO or Rh incompatibility
• The donor's and recipient's ABO and Rh blood types must be matched for compatibility for a transfusion
• If they are incompatible, the recipient's antibodies attach to the transfused RBCs and causes rapid lysis

Etiology of Hemolytic Transfusion Reactions

• The ABO blood group system types are A, B, AB, and O.
• Antibodies are continually made naturally for A or B antigens that a person does not have
• People with blood type O are universal donors because they do not have A or B antigens to be sensed as foreign by the recipient's anti-A or anti-B antibodies.
• People with type AB blood are universal recipients because they do not make anti-A or anti-B antibodies.
• Rh antigens are present on the RBC surface in people who are Rh+
• Antibodies may form for other types of RBC antigens due to prior sensitization, most often from previous blood transfusion or pregnancy.
• A person who is Rh+ typically has the D antigen
• A person who is Rh- does not have the D antigen.
• antibodies are present in those who are Rh- only after a sensitizing event.
• Those who are Rh+ can receive Rh- blood. Those who are Rh- cannot receive Rh+ blood
• When maternal and fetal Rh antigens are different, the mother becomes sensitized by the fetal Rh type and develops antibodies that can affect future fetuses.
• For example, an Rh0(D)-negative pregnant woman becomes sensitized by an Rh0(D)-positive fetus. As a result, the blood cells of future Rh0(D)-positive fetuses can be destroyed by maternal anti-Rh0(D) antibodies crossing the placenta.
• Signs include low back or chest pain, chills, fever, tachycardia, hypotension, headache, nausea, and or anxiety.
• Direct Coomb's test checks for agglutination.
• Epinephrine, and antihistamines are used to treat this.

Medications used

• Antihistamines block capillary permeability, reduce itching and prevent bronchospasms.
• Corticosteroids reduce inflammation and accumulation of macrophages.
• Sympathomimetics cause vasoconstriction, bronchodilation, and cardiac stimulation

Type III Hypersensitivity Reactions

• A type III hypersensitivity reaction involves immune complexes formed by antigens and antibodies, usually of the IgG type
• Serum sickness and resulting organ inflammation, tissue damage, and necrosis are examples of this.

Serum Sickness

• Rare type III hypersensitivity reaction where antigen-antibody complexes causes nonhuman proteins.
• Exposure to nonhuman antigens is typically through medications such as antivenoms, rabies vaccinations, and immune modulating agents (rituximab).
• Arthralgia, edema, fever, lymphadenopathy, muscle soreness, nausea, rash, and urticaria may occur
• Antihistamines and corticosteroids may be given.

Type IV Hypersensitivity Reactions

• Also called a delayed reaction.
• Occurs with a sensitized T-lymphocyte comes in contact with the particular antigen to which it is sensitized
• The resulting necrosis is caused by the actions of macrophages and the various T lymphocytes involved in the cell-mediated immune response
• Contact dermatitis is an example.

Contact Dermatitis

• Haptens bind to the skin, and 7-10 days later T cells are formed.
• The T cells become activated, and cause a reaction
• Common reaction to poison ivy, latex, special protocols are followed using latex-free gloves and equipment.

Transplant Rejection

• Transplanted living tissue is sensed as being foreign to the immune system
• Lymphocytes become sensitized during an induction phase immediately after the tissue is transplanted
• If immunosuppression is not effective, It will result in varying degrees of transplant rejection
• Tests will including arteriography biopsy, blood tests, scans to diagnose organ trauma

Autoimmune Disorders

• With autoimmune disorders, the immune system no longer recognizes the body's normal cells as self
• They are recognized as antigens instead
• Can include viral infections, smoking or drugs
• Can be discussed by system affected

Systemic Lupus Erythematosus

• It occurs more commonly in black, Hispanic, or American Indian women of child bearing age.
• Most patients with lupus have systemic lupus erythematosus (SLE).
• The classic feature of lupus is the characteristic reddened butterfly rash found over the bridge of the nose that extends to both cheeks
• Tests will include complete blood count, as well as anti DNA, or ANA
• Steroids and cytotoxic drugs will be used to treat this.

Ankylosing Spondylitis

• ankylosing spondylitis is a chronic progressive inflammatory disease primarily of the spine and sacroiliac area.
• Can cause severe back pain, fatigue, anxiety.
• Treatment includes pain relief, ROM excercises

Immune Deficiencies

• When one or more components of the immune system are either completely absent or deficient
• Recurrent infections occur, especially from Staphylococcus and Streptococcus organisms
• hypogammaglobulinemia is an example of this.

Overview of hypersensitivity reactions, focusing on the Gell and Coombs classification (types I-IV). Type 1 hypersensitivity is explored in detail, including the roles of histamine and IgE. Learn about allergic rhinitis, asthma, anaphylaxis, and other related reactions that may range from mild to life-threatening.