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Human Blood Dendritic Cell-Like B Cells Isolated by the 5G9 Monoclonal Antibody Reactive with a Novel 220-kDa Antigen

Rui-Kun Zhong^*, Albert D. Donnenberg, Hai-Fan Zhang, Simon Watkins^*, Jie-Hua Zhou^* and Edward D. Ball^1,*

^* Department of Medicine, School of Medicine, University of California at San Diego, La Jolla, CA 92093; and Department of Medicine, School of Medicine, University of Pittsburgh, Pittsburgh, PA

We developed a murine IgG1 mAb, 5G9, following immunization of a BALB/c mouse 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). mAb 5G9 bound to 40–60% of peripheral blood B cells, weakly reacted with monocytes and granulocytes, and did not bind to erythrocytes, platelets, T cells, or NK cells. mAb 5G9 brightly stained scattered cells in human tonsil sections, which appeared to be dendritic cells (DC) by morphology. mAb 5G9 also stained scattered cells in cytospin slides of monocyte-derived DC with long, thin, beaded membrane processes, morphologically distinct from other monocyte-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 - or -L chain positive. They did not express CD3, CD4, CD5, CD10, CD11b, CD13, CD25, CD56, CD14, CD33, or CD64. Isolated 5G9⁺ cells were potent APCs in allogeneic MLR, compared with 5G9^- PBMC, 5G9^- B cells, monocytes, and monocytes 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 study.