CYTOCHEMICAL DETECTION OF SITES OF ANTIBODY TO HORSERADISH PEROXIDASE IN SPLEEN AND LYMPH NODES

After repeated injection of small amounts of horseradish peroxidase into the perivertebral muscle and footpads of rabbits, certain sites in spleen and popliteal lymph nodes showed intense adsorption of antigen (horseradish peroxidase) during treatment of fixed tissue sections in vitro. The reaction occurred in certain cells, probably plasma cells, and was also positive in the reticulum extending between lymphocytes. These sites were considered to contain antibodies against horseradish peroxidase, since sections from the same block, not treated with antigen in vitro, and corresponding sections from nonimmunized rabbits did not give a similar reaction. The blood sera of rabbits which showed specific binding of antigen in the spleen caused approximately 60% inhibition of horseradish peroxidase activity, but no inhibition was caused by the blood sera of nonimmunized control animals.