The peripheral T-cell pool: regulation by non-antigen induced proliferation?

Despite continuous perturbations, the recirculating lymphocyte pool remains relatively constant. Expansion of the pool is compensated for by cell loss. When the T-cell pool is in deficit, either from a congenital defect or an acquired immunodeficiency, T-cell numbers are restored by extrathymic division-a response that occurs without deliberate provocation. We have considered how the recirculating pool may be stably maintained and how a T-cell deficit might be restored to equilibrium. Recent evidence suggests that depleted T-cell compartments are replenished by CD4 T-cell proliferation in the absence of specific antigen, a response that occurs without engaging the T-cell receptor.