Specificity and functional effects of antibodies to human stem cell factor.

Three monoclonal antibodies (Mabs), 7H6, 4B10 and Genzyme Mab, and a commercially-available polyclonal antiserum (Genzyme) to human Stem Cell Factor (SCF) were compared for their ability to detect native and recombinant SCF in a variety of assays, and for blocking of SCF function. All antibodies were found to bind to the membrane bound isoform as well as soluble SCF and to bind to both glycosylated (yeast MGF) and unglycosylated (E. coli SCF) recombinant factor.

Increased expression of c-Kit or its ligand Steel Factor is not a common feature of adult acute myeloid leukaemia.

Cell surface levels of the receptor tyrosine kinase P145(c-kit), the product of the c-kit proto-oncogens, in a panel of 80 primary adult acute myeloid leukaemia (AML) specimens collected at presentation were quantitated by immunofluorescence and flow cytometry, and compared with levels on CD34+ bone marrow cells from normal donors. Receptor levels on AML blast cells were extremely variable and were similar to, or less than, those on normal stem and progenitor cells. In general P145(c-kit) expression was higher on cells of immature phenotype (FAB M1 and M2).

Epitope mapping and functional studies with three monoclonal antibodies to the c-kit receptor tyrosine kinase, YB5.B8, 17F11, and SR-1.

Three monoclonal antibodies (MAbs) to the human c-kit receptor tyrosine kinase (P145c-kit), derived in independent laboratories, have been extensively used in studies of c-kit expression and the role of its ligand, steel factor (SLF), in hemopoiesis and mast cell differentiation and function. In this study, the relationship between the epitopes they identify, and their effects on SLF binding, receptor internalization, and signal transduction are compared. Epitope mapping studies carried out on the high P145c-kit-expressing cell line HEL-DR showed that SR-1 identifies an epitope independent of those bound by YB5.

c-kit is expressed by primitive human hematopoietic cells that give rise to colony-forming cells in stroma-dependent or cytokine-supplemented culture.

Using monoclonal antibody (MAB) YB5.B8, we have examined the expression of the c-kit protein, the receptor for the hematopoietic cytokine stem cell factor (SCF), on primitive hematopoietic cells. Bone marrow mononuclear cells (BMMNC) enriched for immature cells by differential agglutination using the lectin soybean agglutinin (SBA) were subjected to multiparameter fluorescence activated cell sorting (FACS) based on light-scattering properties, the expression of the c-kit protein and the CD34 antigen, and the retention of the vital fluorescent dye, Rhodamine 123 (Rh123).

Expression of CD31 epitopes on human lymphocytes: CD31 monoclonal antibodies differentiate between naive (CD45RA+) and memory (CD45RA-) CD4-positive T cells.

The CD31 antigen, a member of the immunoglobulin superfamily with a possible cell adhesion function, is expressed on approximately 50% of peripheral blood lymphoid cells at relatively low intensity (10-20% of the level on monocytes). In the accompanying paper we showed that a mAb, 5A2.G5, which identifies a glycosylation-dependent epitope of the CD31 antigen, bound to fewer lymphocytes than two other CD31 mAb, B2B1 and 2BD4, although the 3 antibodies bound equally well to monocytes.