Lymph node activating factor from mixed cultures of allogeneic lymphoid cells: effect on the lymph nodes of euthymic and athymic mice.

The action of "lymph node activating factor" (present in supernatants from 4hr cultures of allogeneic lymphocytes) on the lymph nodes of athymic nu/nu mice, nu/+ hybrids and euthymic BALB/c mice was studied. An increase in lymph node weight, cellularity and changes in lymph node morphology, i.e. an increase of the dense lymphatic tissue of the cortex and paracortex and appearance of follicles with light centers, were found in all mice. Lymphocyte activation evaluated by the presence of lymphocytes with RNA synthesizing nucleoli occurred only in nu/nu mice and nu/+ hybrids. Marked changes in lymph node morphology found in nu/nu homozygotes suggest relation of the lymph node activating factor to mediators acting directly on B cells.