Complement Factor P (Properdin) Quantitative Assay
Complement Factor P (Properdin) Quantitative Assay Developed and Manufactured by Svar Life Science
Size: 1×96 wells
Standard Range: 0 – 200 ng/mL
Incubation Time: 2 hours
Sample Type: Serum, Plasma
Sample Size: 100 µL
Alternative Names: Complement Factor P, Properdin
For Research Use Only
Factor P (Complement P, Properdin, FP) is a positive regulator and an initiator of the alternative pathway (AP) for complement activation. It binds surface-bound C3 and C5 convertases and stabilizes them to amplify the activation cascade. Factor P binding increases the half-life of the convertase complex approximately 10-fold. It is suggested, however debated, that Factor P also can initiate complement activation by binding for example cell surfaces or certain biological substrates, recruiting C3b or C3(H2O) and Factor B and thus initiate the AP pathway. Factor P opposes the negative regulation of Factor H that enhances the dissociation of C3b and Bb and mediates Factor I cleavage of C3b to the inactive iC3b3 (Figure 1). Factor P is not produced in hepatocytes as most complement proteins, but instead by several cell types including monocytes, macrophages, T-cells and granulocytes. It is likely that transient increased concentration of Factor P enhances the AP upon local stimuli. For example, neutrophils have Factor P-containing granules that are secreted upon stimulation and can enhance the platelet-granulocyte aggregate formation.
In plasma, Factor P is present in a concentration of approximately 4-25 µg/mL. Factor P is an elongated 53 kDa glycoprotein that oligomerizes in vivo to dimers, trimers or tetramers (P2, P3 and P4) in a ratio of 26:54:20 (P2:P3:P4) in head to tail structures. Mutations, deficiencies, protein levels as well as protein deposits of Factor P are connected to diseases and disorders summarized by Chen et al. Deficiencies generally increase the susceptibility for meningococcal disease and other infectious diseases. Altered serum levels have been associated with for example C3 glomerulopathy, Lupus Nephritis, sepsis and chronic heart failure and IgA nephropathy.
The Factor P Quantitative Assay is a sandwich ELISA for quantifying human Factor P in, for example, serum or plasma samples. The assay is based on immobilized antibody in a 96-well plate, which captures Factor P present in test samples incubated in the plates. The bound Factor P is detected with a secondary antibody labelled with HRP. The HRP subsequently catalyzes a cleavage of the substrate that induces a color change correlating with the concentration of Factor P in the test sample.