Characterization of immunoglobulin G fragments in liquid intravenous immunoglobulin products

Abstract

Intravenous immunoglobulin (IVIG) products formulated as a liquid instead of a powder have become commercially available. Preferably, such liquid products should not alter after storage outside the refrigerator. Therefore, a thorough characterization of immunoglobulin G (IgG) fragmentation at various storage temperatures is required. Storage experiments with liquid IVIG products from five manufacturers were performed at 4, 25, and 37 degrees C and IgG fragments were analyzed. Storage of liquid IVIG products at 4 degrees C resulted in negligible alterations, whereas an increase of IgG fragments was observed after prolonged storage at elevated temperatures. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis of five liquid IVIG products revealed three IgG fragments (12, 26, and 54 kDa) in all products. Fragments of similar molecular mass were produced upon incubations of IgG with blood-derived proteases. N-terminal amino acid sequencing revealed the cleavage site of these fragments, suggesting human neutrophil elastase to cause the 12-kDa fragment. The presence of elastase in liquid IVIG was confirmed by enzyme-linked immunosorbent assay. The origin of the 26- and 54-kDa fragments, both with an aspartic acid residue at the cleavage site, could not be determined unambiguously. IgG fragmentation in liquid IVIG is negligible when stored in the refrigerator. Only after prolonged storage at elevated temperature does proteolytic degradation of IgG become apparent.