Canine BFU‐e progenitors: Adaptation of a reproducible assay and anatomical distribution

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Abstract
In vitro cloning assays are used increasingly in investigative hematotoxi‐cology and in screening candidate compounds for their hematotoxic potential. To expand these applications, a practical cloning assay for erythroid burst‐forming units (BFU‐e) that uses a microplasma clot (MPC) system was adapted to the dog, a species used extensively in experimental hematology and drug development. This system offers the advantage over the methylcellulose and soft agar culture systems of allowing specimen fixation and, therefore, morphological and cytochemical evaluation. The distribution of BFU‐e among various anatomic sites was assessed using the MPC cloning system, which was modified to optimize the BFU‐e growth. BFU‐e growth required only erythropoietin (Epo) in the culture medium and there was no need for an exogenous source of burst‐promoting activity (BPA). The cloning efficiency was linearly proportional to the plating concentrations of Epo and marrow mononuclear cells (MMC) over a range of 0 to 3 U Epo and 1 × 103 to 3 × 103 MMC per ml of culture, respectively. Increases in concentrations of Epo and MMC beyond these levels were not associated with linear growth. The addition of trans‐ferrin and spleen‐conditioned medium containing a mixture of growth factors (including BPA) reduced BFU‐e growth. The relative concentration of BFU‐e was comparable among samples collected from the iliac crest, femur, and humerus. Serial cultures performed on individual dogs were highly reproducible and there was little variation in BFU‐e activity among dogs of comparable age. It was concluded that the MPC system is a practical and reproducible cloning system for early (BFU‐e), as well as late erythroid colony‐forming units (CFU‐e) in the dog. The concentration of BFU‐e appears comparable throughout the active marrow; therefore, various anatomic sites can be used interchangeably for serial quantitative analysis of this progenitor.