Human blood dendritic cell-like B cells isolated by the 5G9 monoclonal antibody reactive with a novel 220-kDa antigen

We developed a murine IgG1 mAb, 5G9, following immunization of a BALB/c mou se with Daudi cells. By immunoprecipitation, 5G9 reacted with a 220-kDa Ag on Daudi cells, which reduced to four subunits (55, 65, 80, and 85 kDa). mA b 5G9 bound to 40-60% of peripheral blood B cells, weakly reacted with mono cytes and granulocytes, and did not bind to erythrocytes, platelets, T cell s, or NK cells. mAb 5G9 brightly stained scattered cells in human tonsil se ctions, which appeared to be dendritic cells (DC) by morphology. mAb 5G9 al so stained scattered cells in cytospin slides of monocyte-derived DC with l ong, thin, beaded membrane processes, morphologically distinct from other m onocyte-derived DC. Positive selection of blood mononuclear cells with mAb 5G9 and sheep anti-mouse IgG Dynabeads demonstrated an enriched population of DC. By flow cytometry analysis, these cells were CD19, CD20, CD22, CD40, CD44, CD83, CD86, IgD, and HLA-Dr positive and either kappa- or lambda-L c hain positive. They did not express CD3, CD4, CD5, CD10, CD11b, CD13, CD25, CD56, CD14, CD33, or CD64. Isolated 5G9(+) cells were potent APCs in allog eneic MLR, compared with 5G9(-) PBMC, 5G9- B cells, monocytes, and monocyte s cultured in IL-4 and GM-CSF for 24 h. mAb 5G9 defines a novel peripheral blood cell with B cell phenotype and DC morphology and function: DC-like B cells. The significance of this cell in immune responses requires further s tudy.