MI2.{5,7-8} | Immunodiagnostics & Immunological Disorders — Summary & Reflection

REFLECT

Integrative questions to consolidate your learning:

1. A patient with SLE and nephritis has low C3, low C4, a positive ANA with homogeneous pattern, and positive anti-dsDNA. Map the pathological sequence: Which hypersensitivity type causes the glomerulonephritis? What is the role of anti-dsDNA complexes? Why is complement low?

1. A post-transplant patient on cyclosporin develops Pneumocystis jirovecii pneumonia (PJP). Explain why this opportunistic infection occurs, connecting your answer to the mechanism of action of cyclosporin and the specific immune pathway it suppresses.

1. Why might a patient with advanced cervical cancer (HPV-positive) be a candidate for a PD-1 checkpoint inhibitor, and what immune mechanism does this treatment restore? How does this connect to tumour immunology principles?

KEY TAKEAWAYS

Key take-home points from this module:

• Immunodiagnostic tests exploit antigen–antibody interactions: agglutination (Widal, Brucella), precipitation (VDRL, Ouchterlony), ELISA (HIV, HBsAg, dengue), immunofluorescence (rabies DFA, ANA-IIF), flow cytometry (CD4 count), and rapid lateral flow tests (HIV rapid test, malaria RDT).
• The four hypersensitivity types: I (IgE, immediate, anaphylaxis), II (IgG/IgM against cell surface, cytotoxic), III (immune complexes, serum sickness/SLE nephritis), IV (Th1 cells, delayed, Mantoux/contact dermatitis).
• Autoimmune diseases arise from tolerance failure; ANA and specific autoantibodies (anti-dsDNA, anti-CCP, anti-GBM) detected by IIF and ELISA are diagnostic cornerstones.
• Primary immunodeficiencies: XLA (no B cells/Ig), DiGeorge (no T cells/thymus), SCID (no T or B cells), CGD (no oxidative burst — NBT negative); secondary immunodeficiency is dominated by HIV, malnutrition, and immunosuppressive drugs.
• Transplant rejection: Hyperacute (pre-formed antibodies, minutes), acute cellular (CD8+ CTL, days–weeks), chronic (antibody + T cell, months–years). HLA matching, crossmatch, and PRA guide donor selection.
• Tumour immunology: Tumours evade immunity via MHC I loss, PD-L1 expression, and Treg infiltration. Checkpoint inhibitors (anti-PD-1, anti-CTLA-4), CAR-T cells, and cancer vaccines represent applications of immune principles to cancer treatment.