OPSONIC ANTIBODIES TO THE SURFACE M-PROTEIN OF GROUP-A STREPTOCOCCI IN POOLED NORMAL IMMUNOGLOBULINS (IVIG) - POTENTIAL IMPACT ON THE CLINICAL EFFICACY OF IVIG THERAPY FOR SEVERE INVASIVE GROUP-A STREPTOCOCCALINFECTIONS

The surface M protein of group A streptococci (GAS) is one of the majo r virulence factors for this pathogen, Antibodies to the M protein can facilitate opsonophagocytosis by phagocytic cells present in human bl ood, We investigated whether pooled normal immunoglobulin G (IVIG) con tains antibodies that can opsonize and enhance the phagocytosis of typ e M1 strains of GAS and whether the levels of these antibodies vary fo r different MG preparations, We focused on the presence of anti-M1 ant ibodies because the M1T1 serotype accounts for the majority of recent invasive GAS clinical isolates in our surveillance studies, The level of anti-M1 antibodies in three commercial MG preparations was determin ed by enzyme-linked immunosorbent assay (:ELISA), and the opsonic acti vity of these antibodies was determined by neutrophil-mediated opsonop hagocytosis of a representative M1T1 isolate. High levels of opsonic a nti-M1 antibodies were found in all MG preparations tested, and there was a good correlation between ELISA titers and opsonophagocytic activ ity. However, there was no significant difference in the levels of ops onic anti-M1 antibodies among the various MG preparations or lots test ed. Adsorption of MG with M1T1 bacteria removed the anti-M1 opsonic ac tivity, while the level of anti-M3 opsonophagocytosis was unchanged. P lasma was obtained from seven patients,vith streptococcal toxic shock syndrome who received MG therapy, and the level of anti-M1 antibodies was assessed before and after MG administration. A significant increas e in the level of type M1-specific antibodies was found in the plasma of all patients who received IVIG therapy (P < 0.006). The results rev eal another potential mechanism by which MG can ameliorate severe inva sive group A streptococcal infections.