THE TEMPO OF LYMPHOCYTE RECIRCULATION FROM BLOOD TO LYMPH IN THE RAT

Abstract

Radioactively labelled thoracic duct lymphocytes were obtained either by incubation in vitro with 3 H‐uridine or 14 C‐uridine or by giving potential donors repeated injections of 3 H‐thymidine finishing 17 days before thoracic duct cannulation. These labelled TDL were injected i.v. into syngeneic recipients which had been subjected to splenectomy and thoracic duct cannulation on the previous day. The tempo of lymphocyte recirculation from blood to lymph was reflected by the time at which radioactivity was recovered in the thoracic duct lymphocyte output of the recipient. This was measured by scintillation counting of 2‐hourly fractional collections for 36 hr after the injection. Two lines of evidence showed that the majority of small lymphocytes which label intensely with radioactive uridine in vitro were uniform in their ‘migration potential’with a modal blood to lymph transit time of 14–18 hr. By contrast the cells which were labelled in vivo with 3 H‐thymidine included a slower population with a modal transit time of 24–28 hr. These conclusions can be more fully interpreted in the light of recent evidence on thymic‐independent (‘B’) lymphocytes.