--- module: 058-02 language: en chapter: 58 title: "Allergy, Anaphylaxis, Immunodeficiency, Transplantation, and Immune Therapy" module_title: "Systemic hypersensitivity, immune-defect localisation, and transplant complications" source_sha256: d758bc34da93f813abc9a45955092454ea800e62b7296dae96d43b70fa74e654 --- # Hypersensitivity, immune defects, and transplant complications ## Localising immune disorders ### Ask which defensive or regulatory function failed ### Allergy: inappropriate response to harmless trigger ### Immunodeficiency: lost protection at typical sites ### Autoimmunity: effectors turned toward self ### Too much or too little immunity #### Fever, rash, infiltrates, cytopenia fit either ## Immunoglobulin E allergy and recognising anaphylaxis ### Sensitisation: class switch under T-helper signals ### Cross-linking releases preformed and new mediators #### Leak lowers effective volume #### Airway and gut smooth muscle constricts ### Severity not predicted by skin-test wheal ### Anaphylaxis is a clinical diagnosis #### Skin findings absent in profound shock #### Normal pressure does not exclude airway danger ### Uncertainty must not delay adrenaline ## Treating anaphylaxis ### Intramuscular adrenaline first-line #### Alpha-one reverses vasodilation and oedema #### Beta-one supports the heart #### Beta-two bronchodilates, cuts mediator release ### Repeat promptly if no improvement ### Sudden sitting or standing #### Empty-ventricle arrest with low venous return ### Supportive care never replaces adrenaline ### Antihistamines only for itch after stabilisation ### Corticosteroids too slow, no biphasic prevention ### Refractory: infusion and early airway plan ## Follow-up and allergy labels ### Tryptase supports mast-cell activation #### Normal result does not exclude anaphylaxis ### Reconstruct trigger, route, timing, cofactors ### Action plan, autoinjector, technique, referral ### Vague labels cause inferior antibiotics and delay #### Clarify by targeted testing or challenge ## Angioedema and food allergy testing ### Histaminergic: itchy wheals, responds to adrenaline ### Bradykinin: no itch, slower, poor drug response #### Protect airway, arrange targeted inhibitor ### Food testing starts from reproducible phenotype #### Broad panels lower positive predictive value ### Intolerance and coeliac disease are not allergy ### Staple-food removal risks growth failure ## Localising immunodeficiency ### Infection pattern over infection count ### Antibody: sinopulmonary encapsulated bacteria, Giardia ### T-cell: opportunists, diarrhoea, thrush, poor growth ### Neutrophil: deep abscesses, impaired pus ### Terminal complement: invasive Neisseria ### Tests chosen by phenotype #### Infant ranges, protein loss, recent immunoglobulin #### Normal screen does not exclude a strong pattern ## Secondary impairment, asplenia, and viral infection ### Far more common than primary disease ### Net state from combined therapies #### Prophylaxis follows integrated state, not drug name ### Asplenia: rapid encapsulated sepsis #### Fever means immediate assessment ### Antiretroviral therapy starts promptly #### Undetectable load prevents transmission ### Immune-reconstitution syndrome is not failure ## Immune therapy risks ### Glucocorticoids: dose, duration, combination #### Abrupt withdrawal: adrenal crisis and relapse ### Tumour-necrosis-factor blockade breaks granulomas ### B-cell depletion: hypogammaglobulinaemia ### Complement inhibition: meningococcus despite vaccine ### Checkpoint inhibitors release T-cell restraint #### Immune events may lag well behind a dose #### Exclude infection before immunosuppression ### Vaccinate before suppression #### Live vaccines later unsafe #### Inactive responses weaker, recheck antibodies ### Prophylaxis follows cumulative regimen and host ## Solid-organ transplant complications ### Hyperacute, acute, and chronic rejection ### Thrombosis, leak, recurrence, toxicity mimic rejection #### Exclude infection before escalating suppression ### Infection shifts with time after transplant #### Maximal suppression: cytomegalovirus, Pneumocystis ### Calcineurin inhibitors: narrow therapeutic window #### Azole, macrolide, grapefruit interactions #### Interpret trough with timing and adherence ### Never interrupt suppression without a plan ### Non-adherence explored without blame ## Stem-cell transplantation and surveillance ### Donor lymphocytes attack malignancy and host ### Graft-versus-host disease: skin, gut, liver ### Sequential infection risks, revaccination needed ### Pair every benefit with a surveillance map