properdin factor B in serum
Reference interval
- 17-42 mg/dL (Adults)
Principle
The Beckman Array Protein System, in conjunction with the Properdin Factor B (PFB) Reagent Test Kit, is intended for in vitro diagnostic quantitation of PFB of biological fluids by rate nephelometry.
The complement proteins are a group of at least 20 immunologically distinct components in blood & tissue fluids. They are able to interact sequentially with antigen-antibody complexes, with each other, & with cell membranes in a complex but adaptable way to destroy viruses & bacteria &, pathologically, even the host's own cells. Complement proteins are synthesized by the liver & are normally present in the blood as functionally inactive molecules. A sequence of interactions can be activated by antigen-antibody complexes through the 'classical' pathway form C1 to C5, or even by nonantibody initiating factors through the 'alternative' or nonclassical pathway from C3 to C5. Either path leadts to the final membrane attack sequence (C5 to C9 & lysis.) The whole process is controlled by the very short life of many of the intermediates & by the presence of specific inhibitor proteins which are an integral part of the system.
.Properdin Factor B (C3 proactivator) is a beta-globulin with a M.W. of 95,000. Its serum concentration normally is ~ 20 mg/dL.
Clinical significance
Decreased plasma levels seen in diseases associated with marked & prolonged alternative pathway activation (e.g. membranoproliferative chronic glomerulonephritis, SLE severe protein-losing gastroenteropathies, burns).
Decreased synovial fluid values seen in Rheumatoid arthritis, sickle cell disease, in C3b deficiency, disease with decreased synthesis or loss of protein.
The alternative properdin pathway is activated by particulate surfaces (e.g. inulin, zymosan, endotoxin). Factor B is a C3A precursor, which is a C3 convertase subunit that enters the classic complement pathway at the C3 level. Low Factor B levels may be indicative of alternative pathway activation but may also be due to loss in patients with severe protein-losing gastro- enteropathies & burns. Normal levels of C3, C4, & Factor B, in the presence of subnormal CH50 indicate another specific factor deficiency, requiring specialized assays for this deficient factor.
Ba is the activation fragment of Factor B liberated in the alterative pathway, & it possesses chemotactic activity. Bb is the decay product of the alternative pathway enzymes an da macrophage & monocyte spreading factor.
Decreases
- membranoproliferative chronic glomerulonephritis
- systemic lupus erythematosus
- severe protein-losing gastroenteropathy
- burns
Specimen
No special patient preparation is required. 200 uL of serum, CSF or urine. Store sample in freezer until ready for assay. Highly lipemic samples may result in inaccurate determination & should be redrawn on a fasting patient. Plasma is not recommended.
More general terms
Additional terms
- nephelometry
- properdin factor B; complement factor B; C3/C5 convertase; glycine-rich beta glycoprotein (GBC); PBF2 (CFB)