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Results for “Properdin”

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PubMed1986

Isolation and characterization of rabbit properdin of the alternative complement pathway.

Rabbit factor P, which is involved in stabilizing the labile C3 convertase of the alternative complement pathway, was isolated from rabbit serum by a simple two-step procedure: polyethylene glycol precipitation and QAE-Sephadex A-50 column chromatography. The chemical properties, and functional activities of the rabbit P were very similar to those of human P, except that there were slight differences in the SDS-PAGE patterns of limited tryptic digests and in the amino terminal sequences. The molecular weights were estimated to be 58 000 for rabbit P and 59 000 for human P on SDS-PAGE under reducing conditions. The amino terminal 36 residues of rabbit P showed 78% homology to the equivalent region of human P.

Amino Acid Sequence↗
PubMed1993

Properdin.

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Chromatography, Affinity↗
PubMed1988

Biosynthesis of complement factor P (properdin) by the human pre-monocyte cell line (U-937).

The human monocyte-like cell line, U-937, is known to differentiate into macrophage-like cells following stimulation with phorbol myristate acetate (PMA) or interferon-gamma (IFN-gamma). The activated cells have been reported to have enhanced capacity to synthesize C2, C3, Factors B and H. Here, U-937 cells were used as a model system to investigate the effects of immunomodulatory agents on the biosynthesis of Factor P by monocytoid cells. Non-stimulated U-937 cells progressively secreted increasing amounts of Factor P over a 72-hr culture period. The secreted Factor P was hemolytically active. The daily production of Factor P was nearly linear (approx. 2.1 +/- 0.2 ng/10(6) cells; mean +/- SEM). Factor P synthesis was reversibly inhibited by cycloheximide indicating de novo synthesis. Both secreted Factor P and Factor P in normal plasma contained Factor P of heterogeneous molecular sizes and eluted from Sephacryl S-300 gel filtration column as a broad peak (mol. wt 250-800 kDa). The synthesis of Factor P by U-937 cells was augmented 1.8-, 2.1- and 2.5-fold respectively following induction with PMA (30 ng/ml), IFN-gamma (100 U/ml) and LPS (0.1 microgram/ml). Metabolic labeling of U-937 cells and autoradiograms of SDS-PAGE analysis of Factor P immunoprecipitates demonstrated a 54 kDa band in the culture supernate, co-migrating with purified 125I Factor P. Intracellular Factor P however had an apparent mol. wt that was 4000 kDa smaller than secreted Factor P. Thus U-937 cells synthesize a precursor Factor P subunit polypeptide chain which undergoes post-synthetic glycosylation and polymerization to give rise to the oligomers characteristic of native Factor P in fresh plasma. Our data also demonstrate that Factor P synthesis by monocytic cells can be enhanced by immunomodulatory factors or mediators that are generally found at sites of inflammation and immune response.

Cell Line↗