USMLE (Fach) / Immunology (Lektion)

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  • Autoantibodies - Anti-phospholipase A2 receptor 1° membranous nephropathy
  • Autoantibodies - IgA anti-endomysial, IgA anti-tissue ... Celiac disease
  • Autoantibodies - Anti-glutamic acid decarboxylase, ... Type 1 diabetes mellitus
  • Chronic transplant rejection Onset: Months to years CD4+ T cells respond to recipient APCs presenting donor peptides, including allogeneic MHC. Both cellular and humoral components (type II and IV hypersensitivity reactions). Features:- ...
  • Graft-versus-host disease Grafted immunocompetent T cells proliferate in the immunocompromised host and reject host cells with "foreign" proteins → severe organ dysfunction. Type IV hypersensitivity reaction. Features:- Maculopapular ...
  • Lymph node A 2° lymphoid organ that has many afferents, 1 or more efferents. Encapsulated, with trabeculae. Functions are nonspecific filtration by macropahges, storage of B and T cells, and immune response activation. ...
  • Lymphatic drainage associations Cervical: Head and neck Mediastinal: Trachea and esophagusHilar: Lungs Axillary: Upper limb, breast, skin above umbilicus Celiac: Liver, stomach, spleen, pancreas, upper duodenumSuperior mesenteric: Lower ...
  • Spleen Located in LUQ of abdomen, anterior to left kidney, protected by 9th-11th ribs. Sinusoids are long, vascular channels in red pulp with fenestrated "barrel hoop" basement membrane. - T cells are found ...
  • Thymus Located in the anteriorsuperior mediastinum. Site of T-cell differentiation and maturation.- Encapsulated.- Derived from the third pharyngeal pouch.- Lymphocytes of mesenchymal origin. Cortex is dense ...
  • Innate vs adaptive immunity Innate immunity:- Components: Neutrophils, macrophages, monocytes, dendritic cells, natural killer (NK) cells (lymphoid origin), complement, physical epithelial barriers, secreted enzymes.- Mechanism: ...
  • Natural killer cells Lymphocyte member of innate immune system. - Use perforin and granzymes to induce apoptosis of virally infected cells and tumor cells. - Also kills via antigen-dependent cell-mediated cytotoxicity (CD16 ...
  • Major functions of B and T cells B cells: Humoral immunityRecognize antigen – undergo somatic hypermutation to optimize antigen specificity.Produce antibody – differentiate into plasma cells to secrete specific immunoglobulins.Maintain ...
  • Differentiation of T cells Positive selection: Thymic cortex. T cells expressing TCRs capable of binding self-MHC on cortical epithelial cells survive. Negative selection: Thymic medulla. T cells expressing TCRs with high affinity ...
  • Th1 cell Secretes: IFN-γ  Function: Activates macrophages and cytotoxic T cells to kill phagocytosed microbes. Induced by: IFN-γ, IL-12Inhibited by: IL-4, IL-10 (from Th2 cell) Immunodeficiency: Mendelian susceptibility ...
  • Th2 cell Secretes: IL-4, IL-5, IL-6, IL-10, IL-13 Function: Activate eosinophils and promote production of IgE for parasite defense Induced by: IL-2, IL-10Inhibited by: IFN-γ (from Th1 cell)
  • Th17 cell Secretes: IL-17, IL-21, IL-22 Function: Immunity against extracellular microbes, through induction of neutrophilic inflammation. Induced by: TGF-β, IL-1, IL-6Inhibited by: IFN-γ, IL-4 Immunodeficiency: ...
  • Treg Secretes: TGF-β, IL-10, IL-35 Function: Prevent autoimmunity by maintaining tolerance to self-antigens.Identified by expression of CD3, CD4, CD25, FOXP3. Induced by: TGF-β, IL-2Inhibited by: IL-6 Immunodeficiency: ...
  • Macrophage-lymphocyte interaction Th1 cells secrete IFN-γ, which enhances the ability of monocytes and macrophages to kill microbes they ingest. This function is also enhanced by interaction of T cell CD40L with CD40 on macrophages.
  • Cytotoxic T cells Kill virus-infected, neoplastic, and donor graft cells by inducing apoptosis. Release cytotoxic granules containing preformed proteins (eg, perforin, granzyme B). Cytotoxic T cells have CD8, which binds ...
  • T- and B-cell activation APCs: B cells, dendritic cells, Langerhans cells, macrophages.Two signals are required for T-cell activation, B-cell activation, and class switching. T-cell activation:1. Dendritic cell (specialized APC) ...
  • Antibody structure and function Fab (containing the variable/hypervariable) regions consisting of light (L) and heavy (H) chains recognizes antigens. Fc region of IgM and IgG fixes complement. Heavy chain contributes to Fc and Fab regions. ...
  • Immunoglobulin isotypes All isotypes can exist as monomers. Mature, naive B cells prior to activation express IgM and IgD on their surfaces. They may differentiate in germinal centers of lymph nodes by isotype switching (gene ...
  • Antigen type and memory Thymus-independent antigens: Antigens lacking a peptide component (eg, lipopolysaccharides from gram ⊝ bacteria); cannot be presented by MHC to T cells. Weakly immunogenic; vaccines often require boosters ...
  • Complement System of hepatically synthesized plasma proteins that play a role in innate immunity and inflammation. Membrane attack complex (MAC) defends against gram ⊝ bacteria. Activation pathways:- Classic ...
  • Cytokines secreted by all T cells Interleukin-2: Stimualtes growth of helper, cytotoxic, and regulatory T cells, and NK cells. Interleukin-3: Supports growth and differentiation of bone marrow stem cells. Functions like GM-CSF.
  • Respiratory burst (oxidative burst) Involves the activation of the phagocyte NADPH oxidase complex (eg, in neutrophils, monocytes), which utilizes O2 as a substrate.Plays and important role in the immune response → rapid release of reactive ...
  • Interferon-α and -β A part of innate host defense against both RNA and DNA viruses.  Interferons are glycoproteins synthesized by virus-infected cells that act on local cells, "priming" them for viral defense by downregulating ...
  • Cell surface proteins T cells: - TCR (binds antigen-MHC complex)- CD3 (associated with TCR for signal transduction)- CD28 (binds B7 on APC) Helper T cells: CD4, CD40L, CXCR4/CCR5Cytotoxic T cells: CD8Regulatory T cells: CD4, ...
  • Live attenuated vaccien - MMRV- Yellow virus- BCG- Influenza (nasal)- Polio (sabin)- Rotavirus- Adenovirus (nonattenuated, given to military recruits)- Smallpox Microorganism loses its pathogenicity but retains capacity for ...
  • Killed or inactivated vaccine - Rabies- Influenza (injected)- Polio (salk) (k for killed)- Hepatitis A Pathogen is inactivated by heat or chemicles. Maintaining epitope structure on surface antigens is important for immune response. ...
  • Subunit - Hepatitis B (HbsAg)- HPV (types 6, 11, 16, and 18)- Acellular pertussis (aP)- Neisseria meningitidis (various strains)- Streptococcus pneumoniae- Haemophilus influenzae type b Includes only the antigens ...
  • Toxoid - Clostridium tetani- Corynebacterium diphtheriae Denatured bacterial toxin with an intact receptor binding site. Stimulates the immune system to make antibodies without potential for causing disease. ...
  • Type 1 hypersensitivity Anaphylactic and atopic – two phases:- Immediate (minutes): antigen crosslinks preformed IgE on presensitized mast cells → immediate degranulation → release of histamine (a vasoactive amine) and ...
  • Type II hypersensitivity Antibodies bind to cell-surface antigens → cellular destruction, inflammation, and cellular dysfunction.Direct Coombs test – detects antibodies attached directly to the RBC surface.Indirect Coombs ...
  • Type III hypersensitivitiy Immune complex–antigen-antibody (mostly IgG) complexes activate complement, which attracts neutrophils; neutrophils release lysosomal enzymes.- Can be associated with vasculitis and systemic manifestations. ...
  • Type IV hypersensitivity Two mechanisms, each involving T cells:1. Direct cell cytotoxicity: CD8+ cytotoxic T cell kill targeted cells.2. Inflammatory reaction: effector CD4+ T cells recognize antigen and release inflammation-inducing ...
  • Blood transfusion reaction Allergic/anaphylactic reaction: Type I hypersensitivity reaction against plama proteins in transfused blood. IgA-deficient individuals must receive blood products without IgA.- Urticaria, pruritus, fever, ...
  • Transplant rejection Hyperacute: within minutes- Pre-existing recipient antibodies react to donor antigen (type II hypersensitivity reaction), activate complement- Widespread thrombosis of graft vessels → ischemia/necrosis- ...
  • Infections in immunodeficiency ↓ T-cells:- Bacteria: Sepsis- Viruses: CMV, EBV, JC virus, VZV, chronic infeciton with respiratory/GI viruses- Fungi/parasites: Superficial, local Candida, PCP, Cryptococcus ↓ B-cells:- Bacteria: ...
  • Systemic mastocytosis Clonal mast cell proliferation occurs in the bone marrow, skin, and other organs.- Often associated with mutations in the KIT receptor tyrosine kinase.- Cells characterized by prominent expression of ...