[MICRO-05] Immunology, Innate vs Adaptive Immunity, Hypersensitivity Reactions (Types I–IV) & Autoimmunity

MICRO-05 • 9. Pathophysiology

Learning Objectives

Compare the 5 human immunoglobulin classes (IgG, IgA, IgM, IgE, IgD) by structure, placental transfer, complement fixation, and mucosal/mast-cell function.; Contrast MHC Class I (CD8+ cytotoxic T cells, all nucleated cells) vs MHC Class II (CD4+ helper T cells, professional APCs).; Classify Gell and Coombs Hypersensitivity Reactions (Types I, II, III, IV) with drug-induced immunological examples.

Chapter Overview & Core Explanation

The immune system combines rapid front-line innate defences (neutrophils, macrophages, complement) with high-precision adaptive memory (B-cell antibodies and T-cells). When this system overreacts to a drug or allergen, it causes hypersensitivity reactions ranging from immediate anaphylaxis to delayed severe skin rashes.

Key Exam & Clinical Takeaways

• IgG is the only immunoglobulin isotype that crosses the human placenta (via neonatal Fc receptor FcRn), whereas secretory IgA provides mucosal immunity via breast milk (colostrum).
• Stevens–Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) are Type IV (T-cell-mediated) delayed hypersensitivity reactions.

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