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Flashcards in Immunodeficiency Deck (17)
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1

describe X-linked agammaglobulinemia

  • B cells in the bone marrow fail to mature beyond the pre-B cell stage, resulting in a marked decrease or absence of mature B-lymphocytes and serum immunogloublins
  • disease is caused by mutations in the gene encoding a kinase called Bruton tyrosine kinase (BTK)
  • recurrent pyogenic infections

2

describe IgA and IgG subclass deficiency

  • results from failure in terminal differentiation of B cells
  • IgA deficiency is most common
    • risk of anaphylactic shock during blood transfusion due to reaction against donor IgA
  • patients tend to develop immune complex disease
  • susceptible to pyogenic infections

3

describe X-linked hyper-IgM syndrome

  • characterized by defective B cell heavy-chain isotype (class) switching so that IgM is the major serum antibody and by severe deficiency of cell-mediated immunity against intracellular microbes 
    • caused by mutations in CD40L (on T cells) 
  • susceptible to pyogenic infections

4

describe common variable immunodeficiency (CVID)
 

  • characterized by poor antibody responses to infections and reduced serum levels of IgG, IgA and IgM
  • underlying causes of CVID include defects in various genes invovled in B cell maturation and activation
  • recurrent pyogenic infection
  • may follow viral infection 

5

describe hypogamaglobulinemia of infancy

  • due to delay in IgG synthesis approx. up to 36 months
    • in normal infants, synthesis begins at 3 months
    • all other immunoglobulins are normally expressed 
  • deficiency in various functions of Th cells has been linked to dminished IgG class switch
  • normal B-lymphocytes

6

describe DiGeorge's syndrome

  • results from incomplete development of the thymus and a failure of T-cell maturation
  • T cells are completely absent or presence of few abnormal T cells
    • B cell, plasma cells and serum Ig levels are detected but in subnormal levels
  • most common are intracellular infxns such as viruses and yeast infxns such as Candida albicans and Pneumocystis carinii but pts should be able to cope with most common bacterial infxns
  • should never be immunized with live attenuated viral vaccines

7

describe ataxia-telangiectasia

  • associated with a lack of coordination of movement (ataxia) and dilation of small blood vessels of the facial area (telangiectasia)
  • T-cells and their functions are reduced to various degrees
  • B-cell numbers and IgM concentrations are normal to low

8

describe Wiskott-Aldrich syndrome

  • X-linked disease caused by a mutation in a gene that encodes a protein responsible for actin cytoskeleton rearrangement; because of the proteins absence, platelets and leukocytes do not develop normally, are small and fail to migrate normally
  • associated with normal T-cell numbers with reduced functions, which get progressively worse
  • IgM concentrations are reduced but IgG levels are normal
    • both IgA and IgE are elevated
  • boys with this syndrome develop severe eczema

9

describe bare leukocyte syndrome

  • caused by failure to express class II MHC molecules, as a result of mutations in the transcription factors that normally induce class II MHC expression
    • some individuals have a defect in their TAP gene and can't express class I MHC and are also deficient in CD8 T cells
  • profound decrease in CD4 T cells, because of defective maturation of these cells in the thymus and defective activation in peripheral lymphoid organs

10

describe cyclic neutropenia

  • marked by low numbers of circulating neutrophil approx. every 3 weeks
  • the neutropenia lasts about a week during which the patients are susceptible to infection; the defect appears to be due to poor regulation of neutrophil production

11

describe leukocyte adhesion deficiency

  • leukocytes lack the complement receptor CR3 due to a defect in CD11 or CD18 peptides and consequently cannot respond to C3b opsonin

12

describe X-linked SCID

  • due to a defect in gamma-chain causing impaired signalling through IL-2 as well as IL-4, -7, -11 and -15
    • all involved in lymphocyte proliferation/differentiation
    • when the gamma chain is not functional, immature lymphocytes, especially pro-T cells, cannot proliferate

13

describe autosomal SCID

  • caused by mutations in the ADA gene, which is involved in the breakdown of adenosine
    • deficiency of ADA leads to the accumulation of toxic purine metabolites in cells that are actively synthesizing DNA, namely, proliferating cells
    • lymphocytes are particularly susceptible to injury because these cells undergo tremendous proliferation during their maturation
  • ADA def. results in a block in T cell maturation more than in B cell maturation

14

describe the effects of corticosteroids

  • cause changes in circulating leukocytes
  • depletion of CD4 cells
  • decreased in circulating eosinophils and basophils
  • inhibition of T cell activation and B cell maturation
  • inhibits cytokine production

15

describe the effects of methotrexate

  • structural analogue of folic acid
  • blocks folic acid dependent synthetic pathways essential for DNA synthesis
  • prolonged use for treatment reduces immunoglobulin synthesis

16

describe the effects of cyclosporin

  • have severe effects on T cell signalling and functions
  • binds to immunophilins which are believed to have a critical role in signal transduction
  • also inhibit IL-2 dependent signal transduction

17

describe Duncan syndrome (X-linked lymphoproliferative syndrome)

  • caused by functional suppression of T cells that renders them incapable of killing EBV-infected B cells
    • as a result, T cells proliferate leading to increased risk of lymphoma or other lymphoproliferative diseases
  • patients do not present with major symptoms until they are infected with EBV