Immune processes in the course of infection with dysentery bacilli. II. Transfer of immunity by means of serum.

The role of antibodies in immunity to intravenous infection with dysentery bacilli was studied in mice. Serum from animals immunized with a single dose of live dysentery bacilli obtained at a varying intervals of time after immunization transferred immunity to other mice infected with lethal doses of the same bacilli. Passive immunity transferred with serum was diffrentiated. Sera obtained 4 to 8 days after immunization of the donors with sublethal doses of live Shigella sonnei phase I bacilli protected lethally infected recipients by inhibiting multiplication of the bacilli in the spleen and liver. Highest protective activity of this type was found in sera obtained 6 days after immunization of the donors. Sera obtained after 11 days and later protected the recipients from death, but only negligibly inhibited growth of the bacilli in the internal organs of the animals. It is suggested that immunity to intravenous infection with dysentery bacilli in mice follows a biphasic course. In the first phase, between days 4 and 8 after immunization, cell-mediated immunity and a specific humoral factor play the main role. In the second phase, specific immunoglobulins of the IgG class afford protection.