It is known that RNA preparation extracted from lymphoid organs of immunized animals contains a factor which is called immune RNA (iRNA). The author studied the role of iRNA in immune response by assaying with plaque-forming cell (RFC) method. The iRNA was extracted with a phenol method from spleens of mice immunized with sheep red blood cells (SRBC).
The iRNA transferred antigen-specific IgM memory to non-immunized mice. The iRNA extracted 5 days after immunization seemed to have higher activity than that extracted at any other day after immunization. The activity of iRNA was lost by treatment with RNase, but was not lost with amylase, proteinase, or anti-SRBC antiserum. High activity was observed in the iRNA extracted from immunized neonatal mice, in which primary immune response was not demonstrated but immunological memory seemed to be induced. And the activity was demonstrated in the iRNA extracted from mice immunized with a low dose of SRBC, with which primary immune response was not initiated but immunological memory seemed to be initiated.
Conclusively, iRNA seemed to play some important roles in the induction of immunological memory.