Studies on the Immune Response of Guinea Pigs to the Envelope Substance of Pasteurella Pestis

Given a weight-adjusted dose, mice excreted an excess of Fraction I two to three times faster than guinea pigs, which explains former difficulties in detecting immunounresponsiveness in mice. The rapidity of elimination of further Fraction I by immunounresponsive guinea pigs 90 days after a primary excess in oil may prevent further stimulation of antibody production in some animals, thus resulting in partial, rather than complete, immunity. Hyperimmune animals were not easily made immunounresponsive. Immunity to Fraction I once established was solid and not easily overwhelmed. Serologic response of guinea pigs to graded doses of Fraction I approaching excess 21 days after injection or over a long period after a single large excess indicates a limited plateau of antibody production to excess Fraction I. This and previous studies indicate immunounresponsiveness of guinea pigs to excess Fraction I in oil adjuvant to be a temporary long delay in immunity resulting from a prolonged blockade of elements of the RES by finely divided state of the antigen, producing a saturation of a limited plateau of antibody production by this system. These inhibiting factors are partially overcome 3 to 6 months later by a gradually appearing antibody excess stimulated from within or by booster inoculation from without. Complete immunity was not obtained because of the rapidity of excretion of later immunizing doses, appearing slowly from the encapsulated injection site or as booster injections.