Treatment potential of pathogen-reactive antibodies sequentially purified from pooled human immunoglobulin

Intravenous immune globulin (IVIG), pooled from human blood, is a polyspecific antibody preparation that inhibits the super-antigenic proteins associated with streptococcal and staphylococcal toxic shock, and the Shiga toxin. In addition to this toxin-neutralising activity, IVIG contains other pathogen-reactive antibodies that may confer additional therapeutic benefits. We sought to determine if pathogen-reactive antibodies that promote opsonophagocytosis of different organisms can be sequentially affinity-purified from one IVIG preparation.

Antibodies that recognise cell wall antigens of Streptococcus pyogenes, Staphylococcus aureus, and vancomycin-resistant enterococcus (VRE) were sequentially affinity-purified from a single preparation of commercial IVIG and opsonophagocytic activity was assessed using a flow cytometry assay of neutrophil uptake. Non-specific IgG-binding proteins were removed from the S. aureus preparations using an immobilised Fc fragment column, produced using IVIG cleaved with the Immunoglobulin G-degrading enzyme of S. pyogenes (IdeS). Affinity-purified anti-S. aureus and anti-VRE immunoglobulin promoted significantly higher levels of opsonophagocytic uptake by human neutrophils than IVIG when identical total antibody concentrations were compared, confirming activity previously shown for affinity-purified anti-S. pyogenes immunoglobulin. The opsonophagocytic activities of anti-S. pyogenes, anti-S. aureus, and anti-VRE antibodies that were sequentially purified from a single IVIG preparation were undiminished compared to antibodies purified from previously unused IVIG.