Effect of thermal injury on splenic myelopoiesis.

Thermal injury increases the number of macrophage progenitors in the bone marrow but leads to a decrease in the number of granulocyte progenitors. In the spleen, thermal injury increases the numbers of myeloid progenitors, but the lineage commitment of these cells is unknown. In this study mice were given a scald burn, and the number of splenic myeloid progenitors as well as their progeny was determined. BrdU uptake was used to monitor the de novo production of splenocytes for 8 days after the burn. Burn injury increased the numbers of splenic granulocyte-macrophage (GM), granulocyte (G), and macrophage (M) progenitors at postburn day 8 by 12-, 11-, and 18-fold, respectively. Scald injury increased the number of mature PMN (CD11b GR1(bright)) in the spleen and increased the number of white pulp monocyte/macrophages. Increased numbers of BrdU-positive PMN and monocyte/macrophages were seen after injury. Burn macrophages produced increased levels of the anti-inflammatory hematopoietic cytokine G-CSF. Our work clearly shows that the increased myelopoiesis observed postinjury leads to the production of mature myeloid cells. However, the effects of thermal injury on progenitors in the spleen and marrow are not equivalent.