Circulating T and B lymphocytes of the mouse: II. Lifespan

Abstract

The average lifespan of circulating lymphocytes was investigated by determining the percentage of labeling of thoracic duct lymphocytes (TDL 5 5 The following abbreviations are used: FCS, fetal calf serum; 3HT, tritiated thymidine; NMS, normal mouse serum; NTx, neonatally thymectomized; POL, polymerized flagellin; TDL, thoracic duct lymphocytes; TxBM, adult thymectomized, irradiated, and marrow protected. ) from mice injected with tritiated thymidine ( 3HT) for various periods. Percentage of labeling of TDL from normal CBA mice, which consist of approximately 85% T cells and 15% B cells, was found to be directly proportional to the time of 3HT administration. This technique thus failed to demonstrate the presence of more than one population of lymphocytes. Less than 50% of TDL were labeled after 3HT injection for 8 weeks. Percentage of labeling of TDL from nude mice (which consist solely of B cells) was likewise found to be directly proportional to the duration of 3HT injection but occurred at a rate three to four times faster than in non-T cell-depleted CBA mice. Further experiments, in which a marker for B cells was used, allowed the rate of 3HT labeling of B cells to be studied in normal CBA mice. These data corroborated the findings in nude mice and indicated that, with regard to lifespan, thoracic duct B cells consisted of a single population with an average lifespan of 5–7 weeks. Similarly it was calculated that the average lifespan of thoracic duct T cells was in the order of 4–6 months. Studies on the rate of formation of TDL during prolonged thoracic duct drainage of normal CBA mice indicated that the percentage of newly formed cells increased rapidly after 24-hr drainage. The total numbers of newly formed cells, however, were found to remain relatively constant throughout the period of drainage investigated (up to 9 days) except for a transient increase during the second and third day. Newly formed small lymphocytes were found to consist of approximately equal proportions of T cells, B cells, and other “mononuclear” cells which lacked surface markers for either T or B cells. The great majority of large lymphocytes, in contrast, were found to be neither T cells nor B cells and probably belonged to the plasma cell line. In nude mice, production of newly formed lymphocytes during prolonged thoracic duct drainage was found to be very low in comparison with normal CBA mice.