Neonates Support “Homeostatic” Proliferation
The number of lymphocytes in the periphery is maintained at a constant level throughout life. Positive or negative disturbances of such balance by either antigenic challenge or lymphoablative therapies lead to activation of homeostatic regulatory processes including massive activation-induced cell death and homeostatic proliferation of peripheral T cells, respectively (Marrack et al., 2000). Experimentally, it has been well demonstrated that lymphopenic environments generated by irradiation or genetic manipulation drives the proliferation of transferred na ve T cells, which rarely divide in their normal environment (Goldrath and Bevan, 1999). It has been argued that this process is fundamentally different from antigen-driven proliferation, implying that different mechanisms are involved (Clarke and Rudensky, 2000). Both the physiologic significance and mechanisms of homeostatic proliferation are poorly understood.
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