Immune phenotype of canine hematopoietic progenitor cells

The immune phenotype of canine hematopoietic progenitor cells was studied by immunoseparation and culturing of separated cells. Two separation methods were used, the magnetic cell sorting system (MACS) and the fluorescence activated cell sorter (FACS). For separation rat anti dog antibodies Dog 13 and Dog 14 directed against Thy-1, and Dog 26 as well as cross-reactive mouse anti human antibodies IOT2a and 7.2 directed against MHC class II were used. Separated cell populations were cultured in semisolid agar before and after long-term culture on a pre-established irradiated stromal cell layer. After 28 days, adherent and nonadherent cells were harvested from long-term culture. The MACS system allowed separation of cells into positive and negative fractions. Long-term culture-initiating cells (LTC-IC) were found in both the Thy-1⁺ and the Thy-1^- fraction, but the content of LTC-IC was higher in the Thy-1⁺ fraction. The MACS system did not allow separation of progenitor cells according to the expression of MHC class II antigen detected by Dog 26 and the cross-reactive antibodies IOT2a and 7.2. In contrast to the MACS system the FACS allowed separation of negative, low-positive and high-positive cell populations. Low-positive fractions were well defined for Thy-1 and less well defined for MHC class II. CFU before and after long-term culture were exclusively observed in the low positive fraction (Thy-1(lo+)). Using MHC class II antibody Dog 26 LTC-IC were found mainly in the negative and low positive fraction, and CFU were observed mainly in the low and high positive fraction. In conclusion pluripotent canine hematopoietic precursor cells are low positive for Thy-1 and for MHC class II. In this respect canine hematopoietic progenitor cells are comparable to those of mouse and man.