The in vivo functions and properties of persisting cell-stimulating factor

We present evidence that persisting (P) cell-stimulating factor (PSF), a T cell lymphokine, is produced and active in vivo. Mice injected in one footpad with keyhole limpet haemocyanin or intravenously with sheep erythrocytes had substantial increases in numbers of splenic P cell precursors; the increase following the sheep erythrocytes did not occur in athymic mice implying a dependence on T lymphocytes. The increase in P cell precursors correlated with the local release of PSF; thus cells from the ipsilateral draining lymph node of mice injected in one footpad with KLH, but not cells from the contralateral node, showed both increased numbers of P cell precursors and the production of PSF. PSF could, in other situations, enter the circulation and exert effects distal to its release. Mice bearing a localized tumour that produced PSF (WEHI-3B), but not those bearing a non-producing subline, showed both a significant increase in P cell precursors in the spleen and bone marrow, and a marked increase in the numbers of mast cells, megakaryocytes, metamyelocytes and polymorphs in the spleen. PSF was detected in the serum of the mice bearing the PSF-producing tumour. Following intravenous injection of PSF into normal mice there was a rapid initial clearance (t 1/2 4 min), followed after 10 mins by a phase of slower clearance (t 1/2 40 min). This was due to removal of PSF rather than inhibition or destruction by serum factors, as when PSF was mixed in vitro with mouse serum for 24 hr at 37 degrees, no activity was lost.