Question

A patient has a genetic disease that prevents her from making the C5 protein. How would this affect the three functions of her complement cascade?

Answer 1

• Complement component 5 is the fifth component of complement encoded by C5 gene
• It plays an important role in inflammatory and cell killing processes.
• This protein is composed of alpha and beta polypeptide chains that are linked by a disulfide bridge.
• C5a and C5b
• An activation peptide, C5a, which is an anaphylatoxin
• It induces smooth muscle contraction ,increased vascular permiability , degranulation of basophills and mast cells and guide lymphocyte to site of infection .
• It is derived from the alpha polypeptide via cleavage with a C5-convertase.
• The C5b can form a complex with the C6 complement component, and this complex is the basis for formation of the membrane attack complex.
• Mutation of C5gene leads to deficiency of C5protein
• Lack of this protein leads recurrent gram negative infection mainly meningitis and extra genital gonorrhea by neisseriae species .
• Liver fibrosis and rheumatoid arthritis occur.

Here in this lady ,she will have recurrent bacterial infection due to deficiency of anaphylatoxin

,liver fibrosis,

rheumatoid arthritis

deficient membrane attack complex

Decreased innate immunity