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Primary Immunodeficiency Diseases

Primary Immunodeficiency Diseases. Primary immunodeficiencies are those in which the defect is intrinsic to the immune ​system, meaning it is genetically determined. Chronic Granulomatous Disease (CGD)

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Primary Immunodeficiency Diseases

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  1. Primary Immunodeficiency Diseases

  2. Primary immunodeficiencies are those in which the defect is intrinsic to the immune ​system, meaning it is genetically determined.

  3. Chronic Granulomatous Disease (CGD) • CGD is a disorder in which polys and monocytes phagocytose but can’t kill bacteria and fungi ​once they’re ingested. This affects phagocyte-rich endothelial organs such as lung, ​liver, spleen, and lymph nodes.

  4. Patients are susceptible to all types of bacteria and fungi that are catalase positive and ​oxidase negative, and​therefore do not produce hydrogen peroxide. • Organisms that are catalase negative (pneumococcus, streptococci, H. influenzae) don’t cause ​particular trouble because they generate hydrogen peroxide.

  5. This occurs because phagocytic cells normally kill ingested microbes by using myeloperoxidase ​in the presence of hydrogen peroxide to fix iodide to the microbial surface. • This iodide ​fixation kills microbes. In normal phagocytes, myeloperoxidase and H2O2 are contained ​in lysosomes that fuse with phagocytes.

  6. In CGD, phagocytic cells can’t generate H2O2, and can’t kill microbes that don’t themselves ​generate peroxide (staph, E coli, aspergillus, candida). • Gene defects that cause peroxide dysfunction may be X-linked or autosomal recessive. Most ​commonly it is the X-linked enzyme Cytochrome b558 that is defective. But various ​genetic defects can cause the same clinical syndrome.

  7. Diagnosis is by NBT dye (only changes color in presence of H2O2), and direct measurement ​of H2O2 production. • Severe Combined Immunodeficiency (SCID) • There are multiple genetic forms of this disease. ADA deficiency is autosomal recessive. IL2 ​receptor deficiency is X-linked recessive. JAK3 and RAG2 deficiencies may also ​cause SCID.

  8. SCID is characterized by severe recurrent infections, since both B and T cells are defective. In IL2 receptor and JAK3 deficiencies, the T cells alone are defective, but this also prevents ​activation of B cells by T cells. • In ADA deficiency, the defect is intrinsic to B/T cells. Adenosine Deaminase (ADA) is part of ​the purine salvage pathway.

  9. When absent, deoxy ATP accumulates and poisons T cells. • Prenatal diagnosis of ADA deficiency is possible. Developmentally, costrochondral flaring of ​the ribs can be seen.

  10. It is now possible to provide enzyme replacement therapy to salvage T cells. We can also ​insert the gene into lymphocytes, and this is the first successful example of gene ​therapy for a genetic disorder.

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