Immunity to Brucella abortus induced in mice by popliteal lymph node restricted strain 19 vaccination

Living vaccines induce immunity by lymphoid organs colonization that persists for a while before subsiding. Brucella abortus 19 vaccine injected into the footpad of mice was shown to colonize the popliteal lymph node and the spleen for at least 15 days before progressive disappearance. Administration of an immune serum before footpad vaccination restricted the colonization to the popliteal lymph node. The serum did not interfere with immunity when this immunity was measured by the virulent challenge spleen count method at least 90 days after vaccination. Immunity induced by lymph node restricted vaccination was very efficient 90 or 180 days after vaccination and was not boosted by a second injection administered 90 days after the first. This immunity was however about 20% lower, expressed in log10 spleen counts, than immunity induced by a non-restricted systemic vaccination which in addition was boosted by a recall. Restricted vaccination may mainly trigger the T-cell limb of immunity, whereas systemic vaccination triggers both humoral and cellular effectors.