engleski

The expression/differentiation pattern of cell antigens and adhesion molecules on the nonadherent population in canine LTMC: A biphasic development of myeloid and lymphoid cells

During maturation of normal hematopoietic progenitors, there appears to be a differentiation-dependent expression of adhesion receptors which may contribute to the homing and lodging of stem/progenitor cells into the marrow and for the eventual release of mature effector cells from the marrow cavity. Using a model of long-term marrow culture (LTMC) we have studied the expression pattern of different lineage cell antigens and cell adhesion molecules on the nonadherent cells in canine LTMC. CD4^+ cells became a major proportion of both the small and large cell subsets by day 8 of culture. Small CD4^+ cells, the majority of which are negative for other T-cell antigens during the first 2 weeks of culture, express low levels of CD4 (CD4^lo) and coexpress granulocytic and/or monocytic markers. These CD4^lo cells have progenitor potential as measured by the long-term culture initiating cell (LTC-IC) assay and differentiate into myeloid (first wave) and lymphoid (second wave) cells. The T cells, which appear in 2-week-old LTMC, respond to Con A but not to alloantigen. At the same time, most of the large cells are CD14^+, CD11b^+, CLA-DR^+ and CD4^lo, while granulocytes are not observed. This phenotypic pattern closely resembles that found on myelomonoytic cells developing from fetal thymic and fetal liver CD34^+ precursors in a model of human fetal thymic organ culture. The cell adhesion molecules - CD44, CD18, L-selectin, CD11a-c as well as VLAa4, dramatically increase from the first week of LTMC, while ICAM-1 and a new b2 cell adhesion molecule, adb2, increased slightly from the third week on. In the large ("monocytic") cell population, adb2 was exclusively expressed by CD4^+ cells. The differentiation pattern of T-cell antigens and adhesion molecules seen in the canine LTMC appear to mimic thse required for developmental interactions between leukocytes and endothelial cells; that is, an early expression of L-selectin and CD44, followed by the integrins, and later on by ICAM-1 and adb2. Our data support the view that in a model of canine LTMC hematopoietic precursors retain their intrinsic developmental potential.

adb2; CD4; cell adhesion molecules; long-term marrow culture

nije evidentirano