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Complement Deficiencies – Primary Immunodeficiency

by Peter Delves, PhD
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    Looking at complement deficiencies, any one of the many different complement components can be affected. For example, if there is a defective gene encoding the complement components C1q, C1r, C1s, C2, C3, C4 or Factor I, there will be impaired clearance of immune complexes. And this can result in the condition, systemic lupus erythematosus which is an autoimmune disease. And typical infections seen when there is deficiency of these particular complement components include a number of pyogenic bacteria. Deficiencies in the later complement components, C6-- C5, C6, C7, C8, C9, Factor D, Properdin; this will lead to a range of other types of infections, particularly disseminated Neisseria infections. MASP-2 deficiency, one sees an increased instance of Streptococcus pneumoniae. And in mannose binding lectin deficiency, which has quite a high prevalence for a primary immunodeficiency, in fact it’s one of the most prevalent primary immunodeficiencies; there is usually no consequence. So most people with mannose binding lectin deficiency don’t even know they’ve got it. And the same is true of another relatively common primary immunodeficiency, which is selective-IgA deficiency. Again, usually other parts of the immune response compensate for the lack, and one doesn’t see a greatly increased instance of particular infections. One interesting complement regulatory component deficiency is paroxysmal nocturnal hemoglobinuria (PNH). In this disease, there is a mutation in the PIG-A gene. This encodes an α-1,6-N-acetyl-glucosaminyltransferase, which results in an inability to synthesize the glycosyl phosphatidylinositol, or GPI anchors. And a lack of these GPI anchors mean that complement control proteins, CD55 and CD59 are absent from the surface of erythrocytes. And this means that these erythrocytes are susceptible to complement-mediated lysis. So normally, CD55 which requires a GPI anchor to hold it on to the cell surface of the erythrocyte, this molecule CD55 inhibits the C3 convertase, which...

    About the Lecture

    The lecture Complement Deficiencies – Primary Immunodeficiency by Peter Delves, PhD is from the course Immunodeficiency and Immune Deficiency Diseases. It contains the following chapters:

    • Complement Deficiencies
    • Paroxysmal Nocturnal Hemoglobinuria
    • Hereditary Angioedema

    Included Quiz Questions

    1. Neisseria meningitidis
    2. Streptococcus pneumoniae
    3. Staphylococcus aereus
    4. Escherichia coli
    5. Candida albicans
    1. C8
    2. Factor I
    3. C1q
    4. C2
    5. C4
    1. GPI anchors attached CD55 and CD59 to the cell surface, which inhibit complement mediated lysis by inhibiting C3 convertase and insertion of the membrane attack complex
    2. GPI anchors inhibit formation of the membrane attack complex and activation of C3 convertase
    3. GPI anchors protect against the actions of CD55 and CD59
    4. GPI anchors inhibit complement mediated lysis by inhibiting CD55 and CD59, which inhibits C3 convertase and the membrane attack complex
    5. GPI anchors attached CD55 and CD59 to the cell surface, attracting C3 convertase which protects against the membrane attack complex

    Author of lecture Complement Deficiencies – Primary Immunodeficiency

     Peter Delves, PhD

    Peter Delves, PhD


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