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Long‐term immunoglobulin G production by transplanted thymus cells

Two sublines of CBA/H mice congenic for the Igl allotype locus were used to study donor‐allotype IgG2a concentrations in the serum of mice injected intravenously with thymus cells. High concentrations (up to several mg/ml) were found in x‐irradiated recipients(exposed to 650 rad, or to 900 rad with a restorative injection of fetal liver cells). The highest concentrations were seen 1–2 months after injection, but detectable quantities were still present in most individuals after 377 days. No donor‐allotype Ig was detected in non‐irradiated recipients. Cell for cell, lymph node cells were about as efficient as thymus cells at transferring IgG production. Although pluripotent hema‐ topoietic stem cells were found in the thymus, their concentration (about 10−8) was too low to account for the results. It is suggested that the thymus contains B lymphocytes, or their precursors, with considerably greater powers of self‐maintenance and expansion than are possessed, on average, by the B lymphocytes in lymph nodes.