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To define the cellular targets for c-kit ligand (KL) and to study their functional properties and composite antigenic profile, we isolated cells expressing c-kit receptor (KR) from bone marrow (BM), peripheral blood, and fetal liver (FL) using immunoadherence to a recently obtained antibody (SR-1) against the human KR. Cells isolated by this approach (designated SR-1Ad) have the morphology of blasts and represent 1% to 4% of the original BM or FL populations. SR-1Ad cells from either source are highly enriched in progenitors (12% to 73%) and respond to KL in distinct patterns. In SR-1Ad cells from BM, the greatest impact of KL stimulation is on burst-forming units-erythroid (BFU-E), whereas in SR1-Ad cells from FL, the most significant KL effect is on a mixed erythroid/nonerythroid progenitor (erythroid/macrophage, colony-forming unit-mix CFU-Mix). When antibody SR-1 is continually present in culture, it neutralizes the effects of added KL. Furthermore, in the absence of added KL, it greatly diminishes the erythropoietin- and interleukin-3-dependent BFU-E growth in BM; whereas in FL, a wider spectrum of inhibition is observed, with CFU-Mix most severely curtailed. SR-1Ad cells coexpress other progenitor-associated antigens in a combination reflecting the dominant presence of erythroid progenitors (high expression of CD34, DR, CD38, and Ep-1; low expression of CD33). Several cytoadhesion molecules, ie, alpha L/beta 2 and alpha 4/beta 1 integrins, and intercellular adhesion molecule 1 and homing cell adhesion molecule 1, are also coexpressed. Our data provide new information on the isolation and characterization of KR expressing cells from normal, adult, and fetal hematopoietic tissues. On these biologically relevant target cells, the impact of ligand-induced stimulation or antibody-mediated ablation of KR function has been gauged.
Papayannopoulou et al. (Sun,) studied this question.