Despite earlier evidence to the contrary, it has recently been claimed that most B lymphocytes, including lymph node (LN) and thoracic duct B cells, are short-lived cells of recent marrow origin. To seek direct information on this question, we transferred unprimed LN or thoracic duct B cells from normal mice to xid mice, i.e., mice unresponsive to the T-independent antigen, trinitrophenyl (TNP)-Ficoll. At varying periods after B cell transfer the recipients were challenged with TNP-Ficoll; anti-TNP plaque-forming cells were assayed in the spleen 6 d later. The results showed that the B cell recipients retained responsiveness to TNP-Ficoll for at least 3 mo after transfer. Responsiveness increased within the first 3 wk but then remained relatively constant. These findings imply that, at least for TNP-Ficoll-reactive cells, B cells residing in LN and thoracic duct lymph are not short-lived cells of recent marrow. Indeed, the data suggest that once the pool of recirculating B cells is fully formed in adult mice, further input of newly formed cells from the marrow into the recirculating pool is very limited.

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