Nucleases in immunity. I. The effect of immunization on RNase and DNase activity in lymphoid tissues.

The level of RNase and DNase in the spleen, lymph nodes and thymus glands of mice immunized with sheep erythrocytes was determined. Within 12 hr after immunization there was a moderate decrease in the level of specific RNase activity in the spleen. The depression persisted for several days and then returned to normal. The level of DNase activity also decreased in the spleen of immunized animals, returning to near normal levels on day 4 to 5 and increasing moderately by day 6 and 8. RNase activity in the lymph nodes and thymus increased rapidly after immunization, reaching a peak level several fold higher than in control animals on days 2 and 6. The level of DNase activity in lymph nodes and thymus was also elevated during the first few days after immunization, but to a lesser extent. The changes in total enzyme activity generally preceded the appearance of haemolytic plaque forming cells. Most of the antibody forming cells were present in the spleen, with peak numbers at day 4. Much fewer antibody forming cells were present in the lymph nodes, and even fewer in the thymus. The relationship between immunogenesis and nucleic acid metabolism in lymphoid tissue was discussed.