Plaque-forming cells in rabbits following stimulation of the appendix with sheep erythrocytes.

Sheep erythrocyte (SRBC) antigen was delivered directly into the lymphoid component of the appendix or via the appendicular artery, followed by ligation or clamping of appendicular vessels. Antigen was also injected intravenously, into the spleen, or into the thymus. Counts of anti-SRBC plaque-forming cells (PFC) in the appendix were compared with counts in the spleen and thymus. None of the injection routes employed resulted in an elevation of PFC activity above background in the appendix. However, delivery of antigen via the appendicular artery caused a marked increase of PFC activity in the spleen. These results and other available evidence point towards a helper-cell function of lymphocytes in the appendix, and therefore suggest a central role of this organ in humoral immunity.