Expression and distribution of the Kit receptor in bovine bone marrow cells

Objective-To characterize the expression and distribution of the Kit recept or in bovine bone marrow cells (BMC) and to define the function of its liga nd, stem cell factor (SCF). Animals-Six 7- to 70-day-old healthy male Holstein-Friesian calves. Procedures-Expression and distribution of the Kit receptor were assessed by use of flow cytometry with monoclonal antibodies (mAb) against the bovine Kit protein. Using Giemsa-stained centrifuged preparations, the histologic appearance of Kit receptor positive (Kit(+)) BMC were evaluated. Semisolid cultures supplemented with granulocyte colony-stimulating factor (G-CSF) an d SCF were used to measure the colony formation capacity of Kit(+) BMC. Results-The Kit receptor was expressed on approximately 18% of total BMC. M ost of Kit(+) BMC did not coexpress lineage markers, but a small subset of this population did coexpress CD3. The Kit(+)CD(3-) BMC were a heterogeneou s cell population comprising blast-like cells such as myeloblasts, promyelo cytes, rubriblasts, and prorubricytes. Conversely, Kit(+)CD(3+) BMC had a l ymphocyte-like appearance. Kit(+) BMC formed colonies in semisolid culture with G-CSF, whereas Kit BMC failed to grow. Addition of SCF to G-CSF result ed in superadditive enhancement in colony numbers and size. Conclusions-The Kit receptor is expressed primarily on immature blood cells in bovine bone marrow, and Kit(+) BMC contain hematopoietic progenitor cel ls that are reactive to G-CSF. In addition, SCF synergizes with G-CSF to st imulate colony formation by these cells. Our results suggest that the Kit r eceptor and its ligand, SCF, are involved in early stages of granulopoiesis in calves.