Intraaortic hemopoietic cells are derived from endothelial cells during ontogeny

We have investigated the developmental relationship of the hemopoietic and endothelial lineages in the floor of the chicken aorta, a site of hemopoietic progenitor emergence in the embryo proper. We show that, prior to the onset of hemopoiesis, the aortic endothelium uniformly expresses the endothelium-specific membrane receptor VEGF-R2. The onset of hemopoiesis can be determined by detecting the common leukocyte antigen CD45. VEGF-R2 and CD45 are expressed in complementary fashion, namely the hemopoietic cluster-bearing floor of the aorta is CD45(+)/VEGF-R2(−), while the rest of the aortic endothelium is CD45(−)/VEGF-R2(+). To determine if the hemopoietic clusters are derived from endothelial cells, we tagged the E2 endothelial tree from the inside with low-density lipoproteins (LDL) coupled to DiI. 24 hours later, hemopoietic clusters were labelled by LDL. Since no CD45(+) cells were inserted among endothelial cells at the time of vascular labelling, hemopoietic clusters must be concluded to derive from precursors with an endothelial phenotype.

Anti-apogens and anti-engulfens: monoclonal antibodies reveal specific antigens on apoptotic and engulfment cells during chicken embryonic development

We have isolated a group of monoclonal antibodies that specifically recognize either apoptotic or engulfment cells in the interdigit areas of chicken hind limb foot plates, and throughout the embryo. Ten of these antibodies (anti-apogens) detect epitopes on dying cells that colocalize to areas of programmed cell death, characterized by the presence of apoptotic cells and bodies with typical cellular and nuclear morphology. Our results indicate that cells destined to die, or that are in the process of dying, express specific antigens that are not detectable in or on the surface of living cells. The detection of these apoptotic cell antigens in other areas of programmed cell death throughout the chick embryo indicates that different cell types, which form specific tissues and organs, may utilize similar cell death mechanisms. Six of the monoclonal antibodies (antiengulfens) define a class of engulfment cells which contain various numbers of apoptotic cells and/or apoptotic bodies in areas of programmed cell death. The immunostaining pattern of the anti-engulfen R15F is similar to that of an antibody against a common leukocyte antigen, suggesting the participation of cells from the immune system in the removal of apoptotic cell debris. These novel monoclonal antibody markers for apoptotic and engulfment cells will provide new tools to assist the further understanding of developmental programmed cell death in vertebrates.

Phenotypic similarities and differences between CALLA-positive acute lymphoblastic leukemia cells and normal marrow CALLA-positive B cell precursors

Expression of differentiation markers in common acute lymphoblastic leukemia (cALL) cells from 25 patients was compared with subpopulations of normal common ALL antigen (CALLA) (CD10)-positive bone marrow lymphoid cells (cBMLs). In cBML, CD10 intensity is positively correlated with CD34 (MY10) and terminal transferase (TdT) expression and inversely correlated with common leukocyte antigen (CLA), CD20 (B1), and ctyoplasmic mu chain (Cmu) expression. In cALL, CD10 density was inversely correlated with CLA and Cmu expression and strongly correlated with CD34 expression as in cBML. In contrast to cBML, TdT and CD20 expression were not related to CD10 density in cALL. Furthermore, cALL TdT intensity measured by enzyme immunoassay was not related to expression of CD10, CLA, or CD34, but was positively correlated with CD20 expression. Cmu expression in cALL was inversely correlated with expression of CD34 and positively correlated with CLA as in cBML, but showed no association with TdT intensity or CD20 expression in contrast to the relationship found in cBMLs. Analysis of TdT intensity and Cmu expression in sorted subpopulations of cells from individual patients that were positive or negative for CD34, CD20, or CD10 was consistent with the data obtained by comparison of cells from different patients. These results indicate that from patient to patient and within individual patients, cALL cells express the markers CD34, CLA, CD10, and Cmu in a coordinated fashion similar to cBMLs, but demonstrate differences in expression of TdT and CD20 with respect to the marrow cells considered their normal counterparts. The cALL cells that are CD34 positive show increased expression of CD10 and are less likely to be CLA or Cmu positive, suggesting that they may represent a phenotypically less differentiated form of cALL than does CD34-negative cALL.

Phenotypic similarities and differences between CALLA-positive acute lymphoblastic leukemia cells and normal marrow CALLA-positive B cell precursors

Expression of differentiation markers in common acute lymphoblastic leukemia (cALL) cells from 25 patients was compared with subpopulations of normal common ALL antigen (CALLA) (CD10)-positive bone marrow lymphoid cells (cBMLs). In cBML, CD10 intensity is positively correlated with CD34 (MY10) and terminal transferase (TdT) expression and inversely correlated with common leukocyte antigen (CLA), CD20 (B1), and ctyoplasmic mu chain (Cmu) expression. In cALL, CD10 density was inversely correlated with CLA and Cmu expression and strongly correlated with CD34 expression as in cBML. In contrast to cBML, TdT and CD20 expression were not related to CD10 density in cALL. Furthermore, cALL TdT intensity measured by enzyme immunoassay was not related to expression of CD10, CLA, or CD34, but was positively correlated with CD20 expression. Cmu expression in cALL was inversely correlated with expression of CD34 and positively correlated with CLA as in cBML, but showed no association with TdT intensity or CD20 expression in contrast to the relationship found in cBMLs. Analysis of TdT intensity and Cmu expression in sorted subpopulations of cells from individual patients that were positive or negative for CD34, CD20, or CD10 was consistent with the data obtained by comparison of cells from different patients. These results indicate that from patient to patient and within individual patients, cALL cells express the markers CD34, CLA, CD10, and Cmu in a coordinated fashion similar to cBMLs, but demonstrate differences in expression of TdT and CD20 with respect to the marrow cells considered their normal counterparts. The cALL cells that are CD34 positive show increased expression of CD10 and are less likely to be CLA or Cmu positive, suggesting that they may represent a phenotypically less differentiated form of cALL than does CD34-negative cALL.