Opsonic and protective activity of immunoglobulin, modified immunoglobulin, and serum against neonatal Escherichia coli K1 infection.

Because modified immune serum globulin (M-ISG) has been proposed for therapy in neonatal bacterial sepsis, we evaluated it in a suckling rat model of Escherichia coli K1 sepsis. We compared a M-ISG preparation (lot 2581), which was protective against group B streptococcal (GBS) sepsis, with other M-ISG, standard ISG preparations and with adult and cord serum. All immune serum preparations and sera demonstrated opsonic activity against E. coli K1 and were superior to saline in protecting against death due to E. coli K1 sepsis. Survival rates were higher for one M-ISG preparation (lot 2581) than for randomly selected standard immune serum globulin and cord sera but were similar to adult sera in these protection studies. Therapeutic and opsonic activity of standard immune serum globulin and M-ISG prepared from the same donors were similar, suggesting that the different processes used for their manufacture did not affect these activities. Because the M-ISG preparation studied showed protective activity to both GBS and E. coli K1, we studied it further by adsorbing the preparation with GBS and E. coli K1. Opsonic activity to E. coli K1 was removed by E. coli adsorption but not by adsorption with GBS, indicating that this activity was not due to a single cross-reacting antibody. Empirical therapy with M-ISG prescreened for opsonic activity to both E. coli K1 and GBS may be of clinical value. Trials appear warranted to study the pharmacology and efficacy of M-ISG in septic newborns.