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A mouse monoclonal antibody named BU11 which detects an antigen strongly expressed on human plasma cells is described. The antibody stains plasma cells in tonsil sections, fresh and cultured plasmacytoid cells from the bone marrow of patients with multiple myeloma and cells of the plasmacytoid cell line RPMI 8226 used as the immunogen. In vitro studies of pokeweed mitogen (PWM) stimulated peripheral blood B cells and Epstein-Barr virus (EBV) stimulated tonsil B cells show that the antigen is present mainly on cells coexpressing the OKT10 antigen and containing cytoplasmic immunoglobulin (cIg). The BU11 antigen is expressed weakly on some normal B cells and is not present on T cells, monocytes or granulocytes. The antigen is of molecular weight 58kD under reducing conditions and is biochemically distinct from previously described plasma cell antigens.

A collection of new and established FDC-reactive MoAb has been used in an immunohistological study designed to throw light on (a) the nature of FDC (which are of unknown lineage) as judged by their sharing of antigens with other cell types and (b) the reason for the strong expression of some B cell antigens on FDC. The MoAb were tested on: (1) sections of tonsil, (2) sections of lymph nodes from four cases of non-Hodgkin's lymphoma, (3) peripheral blood cells and (4) cells of cultured haemopoietic cell lines. Only one of the ten new MoAb bound to FDC and no other component of the tissues screened. It resembled R4/23, a MoAb known to be specific for FDC. The other nine antibodies showed a range of cross-reactivity patterns involving one or more of the following: monocytes, macrophages, platelets, epithelium, endothelium and connective tissue fibres. Some of the MoAb reacted with B lymphocytes and cells of B lymphoblastoid lines but none showed the restricted FDC-staining pattern associated with MoAb which detect the CD23, P45 antigen. The findings are discussed in terms of the intrinsic or extrinsic nature of the antigens detected.

The monoclonal antibody, AGF2.3, was isolated from mice immunised with the human promyeloid cell line HL60. By immunofluorescence and immunoelectron microscopy the antibody was shown to bind to the nuclear envelope in uninduced HL60 cells. Immunofluorescent staining was reduced to very low levels in HL60 cells induced to mature to monocytes or neutrophils by addition of 12-0-tetradecanoylphorbol-13-acetate or dimethyl sulfoxide respectively. Blood neutrophils did not express the antigen. Weak immunofluorescent staining of cell nuclei was observed in peripheral blood lymphocytes and in sections of normal human kidney, tonsil and skin epithelium. The AGF2.3 antigen was strongly expressed on the nuclei of 21/21 haemopoietic cell lines and 21/25 permanent non-haemopoietic cell lines representing various cell types. In contrast, the antigen was not expressed by any of six primary (untransformed) cell cultures. These included fibroblasts, endothelial cells and keratinocytes. The antigen was expressed in the Q10 SV-40 transformed cell line derived from a non-expressing primary fibroblast culture. AGF2.3 antibody precipitated a protein with an apparent subunit molecular weight of approximately 215 kDa from Triton X-100 extracts of HL60 and HeLa cells labelled with 35S-methionine. This protein was not detectable in extracts of primary skin fibroblasts prepared in parallel. We conclude that AGF2.3 antibody recognises a previously undescribed protein associated with the nuclear envelope which is expressed at high levels in most transformed cell lines but which is weakly expressed or absent in normal tissues and primary cell cultures.