[Protective action of anti-listeria IgG]

It was found that single injection into mice of 70 micrograms IgG against Listeria innocua protected them against lethal action of virulent cell of L. monocytogenes, if antibodies were injected 1-3 weeks before infection. Immune IgG did not exert the protective effect when injected one day before infection. Mice T lymphocytes receiving immune IgG three weeks before infection, exhibited increased ability to direct interactions (cluster formation) with dendritic cells presenting Listeria antigen (LA). At the same time, sera obtained from these animals were blocking the reaction of indirect haemagglutination occurring between antibodies against L. innocula and LA-covered sheep erythrocytes. These results suggest that anti-listerial IgG are inducing in mice production of anti-idiotypic antibodies. Most probably, some of these immunoglobulins imitate determinants of Listeria antigens, copying their three-dimensional structure. They could activate T cells specific against bacterial antigens (1st signal of activation). Introduction of virulent L. monocytogenes cells into mice possessing T cells activated by anti-idiotypic antibodies, could create a second antigenic signal, resulting in intensive elimination of bacteria by mechanisms of specific cellular immunity.