The abolition of the protective effect of Pasteurella septica antiserum by iron compounds.

Ferric ammonium citrate, haematin hydrochloride, soluble haematin, lysed mouse red cells and a variety of purified haemoglobins abolished the protective effect of Pasteurella septica antiserum in mice when the iron compounds were injected intraperitoneally with P. septica. Ferric ammonium citrate was less effective than haematin or lysed red cells when the dose of P. septica was reduced to less than 105. The ability of lysed red cells to abolish protection was greatly reduced if given 4 hours or more after infection. P. septica grew rapidly in unimmunized normal mice. In passively immunized mice the number of viable bacteria declined rapidly after infection. In passively immunized mice given haematin or lysed red cells the growth of bacteria was identical to that seen in unprotected normal mice. Large numbers of dead P. septica or carbon particles did not interfere with passive protection.