Two spatially distant epitopes of human lactoferrin.

Lactoferrin (LF) is an iron binding protein, which may represent a target for antineutrophil cytoplasmic antibodies (ANCA) in patients affected by rheumatoid arthritis, ulcerative colitis, and primary sclerosing cholangitis. Here we describe the production and characterization of two new monoclonal antibodies (MAbs) against human LF. These MAbs (AGM 10.14, an IgG1, and AGM 2.29, an IgG2b) recognize spatially distant epitopes of LF as assessed by cross-blocking experiments. We also demonstrated by indirect immunofluorescence that both MAbs react with ethanol-fixed neutrophil granulocytes showing a perinuclear staining pattern. AGM 2.29 and AGM 10.14 have been utilized as capture and labeled tracer antibody, respectively, in a double determinant immunoassay (DDIA) to measure soluble LF. The results obtained show that this DDIA allows us to quantify even low concentrations of LF, the maximal range of the assay sensitivity being between 12 and 780 ng/ml. Therefore, AGM 10.14 and AGM 2.29 may represent useful reagents for studying the role of autoantibodies to LF as well as for measuring soluble LF, which is a reliable secretory marker of neutrophil activation.