Population doublings of murine CD4+ memory T cells during continuous antigen stimulation in vivo

• Neonatal thymectomy removes self-renewing, naïve CD4+ T cells.
• Neonatal thymectomy generates memory CD4+ T cells to self-antigen on parietal cells.
• The memory CD4+ T cells logarithmically expanded in nude mice, when transferred.
• Life duration of CD4+ memory T cell population was one and a half years.
• The population doublings of memory CD4+ T cells are similar to those of naïve ones.

We investigated the expansion rate of CD4+ memory T cells using a newly developed in vivo system. Neonatal thymectomy abrogates the subsequent production of T cells and induces autoimmune gastritis (AIG) by the activation of CD4+ T cells; this disease was transferred into athymic nude mice through the inoculation of splenic CD4+ memory T cells. The transferred CD4+ T cells increased logarithmically in number during the first 2 months in the spleen of the recipients. The serial transfer of these splenocytes at two-month intervals revealed that the numbers of the AIG-transferable generations were inversely correlated with the age of the first AIG donors. The duration of the AIG-promoting capacity of CD4+ T cells under continuous antigenic stimulation in vivo was approximately equivalent—one and a half years. These results indicate that there exists an intrinsic population doubling limit in memory CD4+ T cells similar to that of self-renewing naïve ones.