Host responses to infection with Yersinia enterocolitica

The mechanism of protective systemic immunity to Y. enterocolitica infection in mice was studied. It was determined that active immunization of mice with heat-killed yersiniae would induce a protective immune response against an intravenous challenge. This protective response was proven to be humoral in nature when it was demonstrated that passively transferred serum, but not cells, protected normal recipients against a lethal challenge. It was also shown that the immune serum caused opsonization of the microorganisms resulting in enhanced phagocytosis and killing of yersiniae by reticuloendothelial organs.