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  • Overview
  • Innate immunity
  • Adaptive immunity
  • Hypersensitivity (survey)
  • Vaccination principles
  • Worked micro‑examples
  • Pitfalls
  • Practice prompts
  • References

Anatomy and Physiology - Immune System

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Type: Study
Divisions: B, C
Participants: Up to 2
Approx. Time: 50 minutes
Allowed Resources: Binders/notes allowed per rules; non‑programmable calculator as permitted.

Overview

Immunology distinguishes rapid innate defenses from specific, memory‑forming adaptive responses. Key tools include complement pathways, antigen presentation, and antibody effector functions.

Innate immunity

  • Barriers: skin, mucosa, cilia, acid, antimicrobial peptides.
  • Cells: neutrophils (phagocytosis), macrophages (phagocytosis/antigen presentation), dendritic cells (professional APCs), NK cells (missing‑self recognition), mast cells/eosinophils (allergy/parasites).
  • Complement (survey): classical (Ab‑mediated), lectin (MBL), alternative (spontaneous) pathways converge on C3 convertase → opsonization (C3b), inflammation (C3a/C5a), MAC (C5b‑C9).
  • Inflammation: PRRs (TLRs) detect PAMPs/DAMPs → cytokines (IL‑1, TNF‑α) → vascular changes, leukocyte recruitment.

Adaptive immunity

  • B cells: clonal selection; somatic hypermutation and class switching (T‑dependent); plasma/memory cells.
  • T cells: TCR recognizes peptide‑MHC; CD4 (MHC II) helper subsets (Th1/Th2/Th17/Tfh) vs CD8 (MHC I) cytotoxic.
  • Antigen presentation: endogenous peptides via MHC I (proteasome/TAP) vs exogenous via MHC II (endosomal); cross‑presentation exceptions.
  • Antibody classes: IgM (primary), IgG (opsonization, placenta), IgA (mucosal), IgE (allergy/parasites), IgD (BCR role). Functions: neutralization, opsonization, complement activation, ADCC.

Hypersensitivity (survey)

  • Type I (immediate, IgE/mast): anaphylaxis, allergies.
  • Type II (antibody‑mediated cytotoxicity): hemolysis (ABO mismatch), Goodpasture.
  • Type III (immune complex): serum sickness, some glomerulonephritides.
  • Type IV (delayed, T‑cell): contact dermatitis, TB skin test.

Vaccination principles

  • Active immunity via antigen exposure; adjuvants enhance innate signals; herd effects depend on R₀ and coverage.

Worked micro‑examples

  1. Complement deficiency
  • C5–C9 deficiency → recurrent Neisseria infections (MAC defect); properdin deficiency affects alternative pathway.
  1. MHC restriction
  • A CD8 T cell specific to peptide X on HLA‑A*02:01 will not recognize X on a different HLA allele (restriction).
  1. Hypersensitivity classification
  • Urticaria minutes after peanut ingestion → Type I; rash 48 h after nickel exposure → Type IV.

Pitfalls

  • Confusing MHC I vs II pathways and which T cell recognizes each.
  • Ignoring antibody class functions in mucosal vs systemic compartments.
  • Overlooking innate–adaptive crosstalk (e.g., cytokines shaping Th subsets).

Practice prompts

  • Trace antigen processing for a viral vs bacterial extracellular protein.
  • Match antibody classes to functions and anatomical sites.
  • Classify clinical vignettes by hypersensitivity type.

References

  • SciOly Wiki – Anatomy & Physiology (Immune)
  • Janeway’s Immunobiology (use summaries)