Figure 2.

Regulation of extramedullary hematopoiesis during immune responses. An example of the regulatory mechanism for EH is illustrated. In the spleen, EH, exemplified by maturation of myeloid progenitors into mature neutrophils and dendritic cells, constitutively occurs at low levels. During infection and inflammation, this process is greatly increased due to activated T cells producing hematopoietic cytokines such as GM-CSF and IL-3. An important negative regulator of EH is the FoxP3⁺ regulatory T cell. FoxP3⁺ regulatory T cells suppress the differentiation of naïve T cells into hematopoietic cytokine-producing effector T cells in response to antigens imparted by antigen-presenting cells. Since it is known that FoxP3⁺ regulatory T cells can suppress more than T cells, there is the possibility that FoxP3⁺ regulatory T cells suppress EH via the regulation of additional target cell types.