Immuno 12

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disorders manifesting as defects in both B and T cell arms of adaptive immunity are classified as

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severe combined immunodeficiency (SCID)

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Breakdown of SCID causes

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50% X-linked; autosomal; half of autosomal and X-linked causes unknown

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what mutation causes half X-linked SCID cases

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cytokine receptor subunit gamma

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what normally signals via this X-linked mutation

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IL-2, IL-4, IL-7, IL-9, and IL-15

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IL-7 fxn

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immature T cell proliferation

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IL-15 fxn

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major cytokine involved in NK cell proliferation and maturation

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what causes half autosomal SCID cases

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mutation in adenosine deaminase (ADA)-involved in breakdown of purines

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what occurs with ADA mutation

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accumulation of toxic purine metabolites in cells that are actively synthesizing DNA

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other cause of autosomal SCID

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mutation in kinase involved in signaling by the gammac cytokine receptor chain (similar to X-linked); rare cases due to mutation in RAG1 or 2 gene

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what is fxn of RAG1 and 2

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encode lymphocyte specific components of VDJ recombinase-required for Ig and T cell receptor gene recombinations and lymphocyte maturation

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most common clinical syndrome caused by block in B cell maturation

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X-linked agammaglobulinemia

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what causes decrease/absence of mature B cells in agammaglobulinemia

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mutation in kinase called B cell tyrosine kinase or Bruton tyrosine kinase (Btk)

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Btk fxn

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activated by pre-B cell receptor and delivers biochem signals that promote maturation

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DiGeorge syndrome

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incomplete dvlp of thymus (and parathyroids) and failure of T cell maturation

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X-linked hyper-IgM syndrome

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defective B cell heavy chain isotype switching, so IgM is major serum antibody; severe deficiency against intracellular microbes with cell-mediated immunity

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what causes X-linked hyper-IgM

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mutation in CD40 ligand; leads to defective T cell-dependent B cell responses and T cell-dependent macrophage activation in cell-mediated immunity

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common variable immunodeficiency

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group of disorders characterized by poor antibody responses to infections and reduced serum levels of IgG, IgA, and often IgM

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bare lymphocyte syndrome

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failure to express class II MHC molecules due to mutations in transcription factors that enduce MHC II expression

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class II MHC fxn

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display peptide antigens for recognition by CD4+ T cells; critical for maturation and activation of T cells

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Chronic granulomatous disease

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mutations in enzyme phagocyte oxidase-unable to kill phagocytized microbes

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phagocyte oxidase fxn

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catalyzes production of microbicidal ROS in lysosomes

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Leukocyte adhesion deficiency

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mutation in integrins or enzymes required for expression of ligands for selectins; leukocytes not recruited normally to sites of infection

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C3 deficiency causes

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severe infections and usually is fatal

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C2 and C4 deficiency

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components of classical pathway-immune complex mediated disease resembling lupus

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why does C2 and C4 lead to lupus like disease when absent

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classical pathway is involved in removal of immune complexes that are constantly being formed during humoral responses

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Chediak-Higashi syndrome

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immunodeficiency in which lysosomal granules of leukocytes do not form normally

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Wiskott-Aldrich syndrome

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eczema, reduced blood platelets, and immunodeficiency; X-linked

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mutation in Wiskott-Aldrich syndrome

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protein that binds various adapter molecules and cytoskeletal components in hematopoietic cells

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Ataxia-telangiectasia

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gait abnormalities, vascular malformations (telangietasia), and immunodeficiency; mutation in DNA repair gene

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why does ataxia-telangiectasia result in immunodeficiency

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during recombination of antigen receptor gene segments-results in defective lymphocyte maturation

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Protein-calorie malnutrition and immune fxn

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deficiencies in virtually all components of immune system

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components of infectious HIV particle

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2 RNA strands within protein core, surrounded by lipid envelope derived from infected host cell (but containing viral proteins)

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how does HIV infect cells

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mainly via gp120-major envelope glycoprotein; binds CXCR4 and/or CCR5 of CD4 cells

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provirus

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integrated viral DNA

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what may account for loss of T cells exceeding HIV infected T cells

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T cells chronically activated -eventual apoptosis via cativation-induced cell death

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what occurs during clinical latency of HIV infected person

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usually progressive loss of CD4+ T cells in lymphoid tissues and destruction of architecture of lymphoid tissues

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normal CD4+ level and level of AIDS

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1500 cells/mm^3 vs 200

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why are CD8+ CLT fxn lowered in AIDS

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CD4+ required for full responses to many viral antigens

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two most common cancers assocaited with AIDS

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B cell lymphoma (EBV) and Kaposi sarcoma (herpesvirus)