Functional analysis of myeloid cell antigens

Based on their structures and homologies to other adhesion receptors, the lymphomyeloid progenitor cell antigen, CD34, the myelomonocytic cell antigen, CD33, and the mature myeloid cell surface molecule, BGPc, are candidates to mediate specific cell-extracellular matrix and/or cell-cell adhesion. This thesis describes the analysis of adhesion of the CD34, CD33 and BGPc molecules to stromal layers formed by long-term bone marrow cultures, extracellular matrix components and various cell lines. BGPc mediated homophilic aggregation of CHO cells transfected with BGPc cDNA as well as binding to carcinoembryonic antigen (CEA) and perhaps another cell surface receptor on HL-60 cells. The CD33 and CD34 defined antigens do not appear to be involved in adhesion to stromal layers; to the extracellular matrix components fibronectin, fibrinogen, laminin, collagen I, III, IV, IX and X and hyaluronic acid; or to other cell surface receptors expressed on Raji, Daudi, MOLT4, CEM, U937, HL-60, KG1 and peripheral blood mononuclear cells. This work also describes the molecular cloning of a murine homologue of the human CD33 myeloid antigen. Two cDNA clones, differing by an 83 nucleotide insertion in the cytoplasmic region were isolated. The insertion generated a shift in the reading frame within the cytoplasmic tail, resulting in two mouse CD33 isoforms, m33-A and m33-B, with distinct cytoplasmic domains and with predicted protein core molecular weights of 37 kD and 45 kD, respectively. The cDNAs and deduced amino acid sequences show extensive similarity to the human CD33 sequence with the highest homology in the first and second Ig-like domains (61% amino acid identity). The most significant divergence between the human and murine proteins occurs in their cytoplasmic portions. Murine CD33 mRNAs were detected in bone marrow, spleen, thymus, brain, liver and in the multipotential progenitor cell line, A4, the myelomonocytic cell line, WEHI 3B, the myeloid cell line. M1 and the macrophage cell line, P388, by Northern analysis. The expression pattern of the murine CD33 homologue suggests that the function of CD33 antigen in haemopoiesis may be conserved between man and mouse