Comparative effects of immunoglobulins and immunoglobulin fragments on the immune response of rabbits

Immunosuppression by passive transfer of antibody has been extensively studied and has resulted in at least one practical human application. Human immunoglobulin G anti-Rho is now used widely in the prevention of Rh antibody production by Rh negative mothers. Although considerable knowledge has accrued concerning the mechanisms involved, many aspects of the role of passive antibody are still uncertain. The principal purpose of this was to determine if the low molecular weight subunit ( ? 160,000) of the IgM molecule is similar to the entire molecule (? 160,000 MW) of IgG and IgM (1,000,000) in regards to its capacity to cause immunosuppression. Rabbits immunized with human erythrocytes and injected with homologous immunoglobulins or their fractions were found to vary quantitatively in their ability to produce antibody. Homologous anti-human erythrocyte IgG exhibited the greatest capability to cause immunosuppression. Homologous, specific IgM appeared much less capable in suppression of antibody production. Homologous IgM low molecular weight fragments had little or no effect on antibody production.