Immunology Flashcards – First Aid for the USMLE STEP 1

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  • Structure of a lymph node
    "Many afferents, 1 or more efferents; encapsulated with trabeculae"
  • Function of lymph nodes
    (1) non specific filtration by macrophages (2) storage and activation of T and B cells (3) antibody production
  • Site of B cell localization and proliferation
    Follicle - located in outer cortex of lymph node
  • Primary follicles
    Dense and dormant
  • Secondary follicles
    Active with pale central germinal centres
  • Medullary cords
    Closely pack lymphocytes and plasma cells
  • Medullary sinuses
    Communicate with efferent lymphatics and contain reticular cells and macrophages
  • Region of cortex between follicles and medulla that houses T cells
    Paracortex
  • Which region of lymph node enlarges in an extreme cellular immune response?
    Paracortex
  • Which region of lymph node is not well developed in DiGeorge syndrome?
    Paracortex
  • Where are high endothelial venules located?
    Paracortex - site through which T and B cells enter from blood
  • Lymph drainage of upper limb and lateral breast
    Axillary node
  • Lymph drainage of stomach
    Celiac lymph nodes
  • Lymph drainage of sigmoid colon
    Colic node --> inferior mesenteric node
  • Lymph drainage of duodenum/ jejunum
    Superior mesenteric node
  • Lymph drainage of rectum (ABOVE pectinate line)
    Internal iliac node
  • Lymph drainage of anal canal (BELOW pectinate line)
    Superficial inguinal node
  • Lymph drainage of testes
    Superficial and deep plexuses --> para aortic nodes
  • Lymph drainage of scrotum
    Superficial inguinal node
  • Lymph drainage of superficial thigh
    Superficial inguinal node
  • Lymph drainage of lateral side of dorsum of foot
    Popliteal node
  • Right lymphatic duct drains..
    Right arm and right half of head
  • Thoracic duct drains...
    Everything EXCEPT right arm/head
  • Sinusoids of spleen
    "Long, vascular channels in red pulp with fenestrated barrel hoop basement membrane Majority of spleen is red pulp"
  • Where are T cells found in spleen?
    Periarterial lymphatic sheath (PALS) within white pulp White pulp = PALS + B cell corona
  • Where are B cells found in spleen?
    Follicles within white pulp of spleen White pulp = PALS + B cell corona
  • Which cells are located in marginal zone of spleen?
    APCs
  • Macrophages in spleen remove...
    Encapsulated bacteria
  • Splenic dysfunction increases susceptibility to which organisms?
    "Encapsulated ""Shin Skis"" Strep, H Flu, Neisseria Meningitidis Salmonella, Klebsiella, Strep (Group B) dec IgM --> dec complement activation --> dec C3b opsonization --> inc susceptibility to encapsulated organisms"
  • Post-splenectomy remnants/results (3)?
    Howell-Jolly bodies (nuclear remnants) Target cells Thrombocytosis
  • Site of T cell differentiation and maturation
    Thymus
  • Thymus is derived from which embryonic derivative?
    "Epithelium of 3rd branchial pouch fully formed at birth --> most active before puberty --> shrinks with age (reversible, e.g. BM transplant)"
  • Lymphocytes are of which embryological origin?
    Mesenchymal origin
  • Cortex of thymus contains...
    Immature T cells
  • Medulla of thymus contains...
    Mature T cells and epithelial reticular cells containing Hassall's corpuscles
  • Where do positive and negative selection occur in thymus?
    Positive selection: cortex Negative selection: corticomedullary junction
  • Positive selection
    MHC restriction: T cells must express TCR capable of binding surface self MHC
  • Negative selection
    Non-reactive to self: T cells with TCR that bind self-Ag with high affinity undergo apoptosis
  • Innate immunity
    Receptors that recognize pathogens are germline encoded; response is fast and non specific with no memory
  • Cells involved in innate immune response
    "Neutrophils, macrophages, dendritic cells, NK cells, and complement note: NK cells are the only innate cell of lymphoid origin"
  • Adaptive immunity
    Receptors undergo V(D)J recombination during lymphocyte development; slow to first exposure but memory response is faster and more robust
  • Cells involved in adaptive immune response
    "T cells, B cells, circulating Ab"
  • Human leukocyte antigen genes code for...
    Major histocompatibility complex
  • Role of MHC
    Present antigen fragments to T cells and bind TCR
  • MHC 1 binds..
    TCR and CD8
  • MHC II binds
    TCR and CD4
  • Which HLA genes code for MHC 1?
    "A, B and C"
  • Which HLA genes code for MHC II?
    "DR, DP and DQ"
  • MHC I is expressed on...
    "Almost all nucleated cells, but NOT on RBCs"
  • B2 microglobulin
    Needed to mediate transport of MHC I to cell surface
  • How is antigen loaded to MHC I?
    Intracellular peptides are loaded in RER proteosomes degrade pathogen --> TAP transports peptide to ER --> MHC-I binds peptide in RER --> complex moves to cell surface
  • How is antigen loaded on MHC II?
    Antigen is loaded following release of invariant chain in an acidified endosome MHC-II binds peptide in endosome --> complex moves to cell surface
  • MHC I mediates...
    Viral immunity
  • dz associated with HLA A3
    Hemochromatosis
  • dz associated with HLA B27
    PAIR: psoriasis ankylosing spondylitis IBD reiter's syndrome
  • dz associated with HLA B8
    Grave's disease
  • dz associated with HLA DR2
    "Multiple sclerosis, hay fever, SLE, goodpasture's"
  • dz associated with HLA DR3
    1. T1DM (not T2!!!) 2. Grave's Disease
  • dz associated with HLA DR4
    "Rheumatoid arthritis, T1DM (not T2!!!)"
  • dz associated with HLA DR5
    "Pernicious anemia, B-12 Deficiency, Hashimotos thyroiditis"
  • DELETEdz associated with HLA DR7
    Steroid-responsive nephrotic syndrome
  • Only lymphocyte member of innate immunity
    NK cells
  • NK cells - mechanism
    Use perforin and granzyme to induce apoptosis of virally infected cells and tumor cells
  • Which cytokines enhance NK cell activity?
    "IL2, IL12, IFN-alpha, IFN-beta"
  • NK cells are induced to kill when...
    (1) exposed to NON-specific activation signal on target cell (2) exposed to ABSENCE of MHC-I on target cell surface
  • Which antibody neutralizes viruses and opsonizes bacteria?
    IgG
  • Which antibodies can activate complemet?
    IgG and IgM
  • Which antibodies sensitize mast cells?
    IgE
  • Which antibodies mediate allergy and type 1 HS reactions?
    IgE
  • Which antibodies mediate type 2 and 3 HS reactions?
    IgG
  • Hyperacute organ rejection is mediated by...
    Antibodies - B cells
  • Acute and chronic organ rejection is mediated by...
    T cells
  • Function of CD4 T cells
    Help B cells make antibodies and produce IFN-y which activates macrophages
  • CD8 T cells function
    Kill virus infected cells directly
  • Delayed type HS reaction is mediated by..
    T cells
  • CD8+ T cells become
    "Cytotoxic T cells which kill virus-infected, neoplastic and donor graft cells"
  • CD4+ T cells become
    T helper cells
  • Which interleukin mediates development of Th1 cells?
    IL-12
  • Which interleukin mediates development of Th2 cells?
    IL-4
  • Which Th cell is important for cell-mediated response?
    Th1 cells
  • Which Th cell is important for humoral response?
    Th2 cells
  • Antigen presenting cells
    "Macrophages, dendritic cells, B cells"
  • Costimulatory signal for Th cell activation
    B7 on APC interacts with CD28 on Th cell
  • Costimulatory signal needed for cytotoxic T cell activation
    IL2 from Th1 cell activates CD8 T cell to kill virus-infected cell
  • Which cytokines from Th2 cell mediate class switching on B cell?
    "IL4, IL5, IL6, IL10"
  • Costimulatory signal for B cell class switching
    CD40 Ligand from Th2 cell binds CD40 on B cell
  • Th1 cell regulates (1) and activates (2) and (3)
    (1) cell mediated response (2) macrophages (3) CD8+ T cells
  • Th1 cells secrete which cytokines?
    IL2 and IFN-y
  • Which cytokine inhibits Th1 cells?
    IL-10 (from Th2 cells)
  • Th2 cells regulate (1) and activate (2)
    (1) humoral response (2) B cells to make antibody (IgE > IgG)
  • Th2 cells secrete which cytokines?
    "IL4, IL5, IL6, IL10"
  • Which cytokine inhibits Th2 cells?
    IFN-y (from Th1 cell)
  • Macrophage-lymphocyte interaction
    ACTIVATED lymphocytes (release IFN-y) and macrophages (release IL1 and TNFa) stimulate one another
  • How do cytotoxic T cells kill cells? What cells are killed?
    "Release cytotoxic granules containing preformed proteins (perforin, granzyme, granulysin) to kill virus-infected, neoplastic, and donor graft cells by inducing apoptosis"
  • Perforin
    Helps deliver content of granule into target cell
  • Granzyme
    "Serine protease, activates apoptosis inside target cell"
  • Granulysin
    "Antimicrobial, induces apoptosis"
  • Fab
    Antigen binding fragment of antibody; made of variable regions of heavy and light chains
  • Idiotype
    Unique antigen binding pocket; only one idiotype expressed per B cell
  • Fc portion
    Constant region of antibody made of carbohydrate side chains; at carboxy terminal
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