Immunology

A high-yield Step 1 review of the four Gell-Coombs hypersensitivity types — IgE (I), antibody/cytotoxic (II), immune-complex (III), and delayed T-cell (IV) — with mechanisms, diagnostic tests, the anaphylaxis-vs-anaphylactoid distinction, and the classic vignette buzzwords boards reward.

A Step 1 high-yield lesson contrasting innate immunity (fast, non-specific, no memory: phagocytes, NK cells, complement, TLRs) with adaptive immunity (slower, antigen-specific, memory: T and B cells), then linking each key cell/molecule to its classic immunodeficiency and infection pattern. Includes comparison and defect-to-disease tables, innate and adaptive clinical vignettes, and standard board mnemonics. Reviewed and signed off as accurate.

A Step 1 high-yield walkthrough of how T cells are educated in the thymus (positive/negative selection, MHC restriction, AIRE) and activated in the periphery (two/three-signal model, checkpoints, Th subsets), each step mapped to the classic immunodeficiency or autoimmune vignette its defect produces.

A Step 1 walkthrough of how B cells convert antigen recognition into high-affinity, class-switched antibody — BCR activation, the CD40L–CD40/AID germinal-center reaction, the five isotypes and their jobs, and the antibody immunodeficiencies (Bruton, hyper-IgM, selective IgA, CVID, Wiskott-Aldrich) mapped to their signature infection patterns.

A Step 1 high-yield walkthrough of MHC/HLA antigen presentation: MHC I (endogenous → CD8) versus MHC II (exogenous → CD4), the proteasome/TAP and invariant-chain/CLIP/HLA-DM loading pathways, the defect-to-disease correlations (bare lymphocyte syndromes types I and II), and the classic HLA disease and drug-hypersensitivity associations.

A Step 1–focused walkthrough of the complement system: the three activation pathways converging on C3, the roles of C3b, the anaphylatoxins, C5a, and the MAC, and the high-yield regulator/component defects mapped to their signature diseases (Neisseria, hereditary angioedema, PNH, and SLE).

A Step 1 high-yield tour of the cytokines that show up on boards — the innate/macrophage set (IL-1, IL-6, IL-8, IL-12, TNF-α), the T-helper subset cytokines and interferons — mapped to their secreting cells, functions, defect-driven diseases (IL-12R deficiency, Job syndrome), and cytokine-directed drugs.

A board-focused map of primary immunodeficiencies organized by the four arms of host defense — B cell, T cell, phagocyte, and complement — linking each defective molecule to its signature infection pattern and syndrome. Includes comparison tables, defect→disease vignettes, and the classic USMLE mnemonics.