Questions
3–5 questions in university semester papers
Difficulty
Medium-Hard
Importance
High yield for MBBS and BMLT/BMRIT university exams
Overview
Immunopathology is the study of immune responses that cause disease, primarily through the failure of protective mechanisms or aberrant reactions against self or harmless antigens. Mastering this topic is essential for clinical understanding of chronic conditions, organ rejection, and failure of immune surveillance. Success in this topic relies on categorizing reactions based on the Gell and Coombs classification and understanding the loss of self-tolerance.
Hypersensitivity Reactions (Gell and Coombs)
Hypersensitivity refers to excessive or aberrant immune responses to antigens that cause tissue damage or disease. It is systematically classified into four types based on the mechanism of injury and the time taken for the reaction to manifest.
- Type I: IgE-mediated, immediate reaction (e.g., Anaphylaxis, Asthma)
- Type II: IgG/IgM-mediated cytotoxic reactions (e.g., Blood transfusion reactions)
- Type III: Immune complex-mediated reactions (e.g., SLE, Post-streptococcal glomerulonephritis)
- Type IV: Cell-mediated (delayed) hypersensitivity (e.g., Contact dermatitis, TB Mantoux test)
Autoimmune Diseases
Autoimmunity occurs when the immune system loses its ability to distinguish between 'self' and 'non-self' antigens, leading to an adaptive immune response against host tissues. These diseases are often multifactorial, involving genetic predisposition combined with environmental triggers.
- Mechanism: Failure of central or peripheral tolerance
- Systemic Autoimmunity: Rheumatoid Arthritis, Systemic Lupus Erythematosus (SLE)
- Organ-specific: Hashimoto thyroiditis, Type 1 Diabetes Mellitus, Multiple Sclerosis
- Role of MHC/HLA complex in genetic susceptibility
Immunodeficiency Pathology
Immunodeficiency states represent the clinical consequences of a compromised immune system, categorized into primary (genetic) or secondary (acquired) disorders. Pathologically, these result in increased susceptibility to opportunistic infections and decreased surveillance against malignancy.
- Primary: Severe Combined Immunodeficiency (SCID), Bruton's Agammaglobulinemia
- Secondary: HIV/AIDS, Malnutrition, Chemotherapy-induced immunosuppression
- Diagnostic hallmark: CD4+ T-cell count reduction in HIV
- Pathogenesis of AIDS: Depletion of CD4 T-helper cells via HIV infection
Exam Tip
Always draw a table comparing the four types of hypersensitivity reactions in your answer—it is the quickest way to gain full marks.
Common Mistakes
- Confusing Type II (cytotoxic) and Type III (immune complex) mechanisms by incorrectly identifying the role of complement fixation.
- Failing to mention the time factor (immediate vs delayed) when describing Type I versus Type IV reactions.
- Treating autoimmune diseases as purely genetic without acknowledging environmental/epigenetic triggers.
More Revision Notes
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