The transfer to rabbits of homologous lymph node cells which have been incubated in vitro with Shigella-trypsin filtrate leads to the appearance of agglutinins to Shigella in the sera of the recipients. In the present study it has been found that the prior injection of the prospective recipients with blood leucocytes from the donor animals prevented the appearance of anti-Shigella agglutinins. The following observations have been made in this system:

1. The degree of the pre-injection effect was found to be a function of the number of leucocytes injected and of the interval between such pre-injection and the transfer of the antigen-incubated lymph node cells.

2. The pre-injection of leucocytes at appropriate intervals could also cause the failure of antibody to appear in sera of recipients of lymph node cells when these were obtained from donor rabbits injected with Shigella, 1, 2, or 3 days prior to cell transfer.

3. Agglutinins failed to appear in cell-transfer experiments after the pre-injection not only of blood leucocytes, but also of lymph node cells, peritoneal exudate cells, or thymus cells of rabbits. This effect was not brought about by pre-injection of erythrocytes of rabbits or leucocytes of chicken, cow, or horse. The pre-injection of leucocytes of human blood had an effect of partial suppression.

4. When the leucocytes for pre-injection were pooled from groups of rabbits, either the prospective donors of the lymph node cells or other rabbits, essentially complete suppression of agglutinin titers occurred regularly. When the leucocytes for pre-injection were obtained from an individual rabbit and the lymph node cells from another rabbit the suppression of the recipients' titers occurred sporadically.

5. When the recipient's own leucocytes were pre-injected the subsequent agglutinin titers were somewhat lower than those of the non-pre-injected controls. When the recipient's whole blood was re-injected as the source of leucocytes the subsequent agglutinin titers were as high as those of the non-pre-injected controls.

6. The pre-injection effect was not obtained if the leucocytes had been heated, frozen and thawed, suspended in distilled water, lyophilized, or treated with sodium iodoacetate. However, sonic oscillation or x-irradiation of the leucocytes had no effect on their capacity to bring about the pre-injection effect.

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