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Udgivelsesdato: februar

Background and Objectives. We explored the expression of LCK and BAFF-R (B-cell activating factor receptor) both of which are known to play a role in signaling and apoptosis, in routine tissue biopsies. It was hypothesized that their expression patterns might yield information on apoptosis as it occurs in normal and reactive lymphoid cells, and also be of value for the detection of lymphoma subtypes. Design and Methods. Both molecules were studied in paraffin-embedded tissue sections and cell lines by immunoperoxidase staining, and were also studied by western blotting. Human tonsillar B-cell subsets were analyzed by flow cytometry for LCK expression. Results. LCK was detected for the first time in germinal centers and, at lower levels, in mantle zone B cells. The presence of LCK in B cells was confirmed by western blotting. Cross-linking surface IgM reduced LCK expression whereas cross-linking surface CD40 appeared to have the opposite effect. BAFF-R was present on mantle zone B cells but absent or weakly expressed in germinal center cells. Most lymphomas of germinal center origin (e.g. follicular lymphoma) and also many mantle cell lymphomas, chronic lymphocytic leukemia (CLL) and most T-cell neoplasms expressed LCK. In contrast, BAFF-R was expressed in a variety of B-cell lymphomas, but often absent in grade 3 follicular lymphomas and diffuse large B-cell lymphomas (DLBCL). Both LCK-positive and BAFF-R-positive DLBCL tended to be of germinal-center phenotype. Interpretation and Conclusions. The reciprocal expression pattern of LCK and BAFF-R in germinal center and mantle zone B cells may reflect their opposing roles in apoptosis. Their detection in lymphoma tissue biopsies may therefore be of clinical relevance in predicting response to treatment.

The JC12 monoclonal antibody recognizes a previously unknown nuclear protein that showed a restricted distribution in normal tonsil and was also overexpressed in a subset of diffuse large B-cell lymphomas. Using this reagent, we expression cloned cDNAs encoding its antigenic target and identified this protein as a novel putative transcription factor, FOXP1. The FOXP1 protein sequence contains predicted domains characteristic of transcription factors, including a winged helix DNA-binding motif, a second potential DNA-binding motif, a C(2)H(2) zinc finger, nuclear localization signals, coiled-coil regions, PEST sequences, and potential transactivation domains. The FOXP1 gene has been mapped to chromosome 3p14.1, a region that commonly shows loss of heterozygosity in a wide range of tumors and which is reported to contain a tumor suppressor gene(s). Using tissue arrays and immunohistochemistry, we demonstrate that both the FOXP1 mRNA and protein are widely expressed in normal tissues. The levels of FOXP1 mRNA were compared in paired normal and tumor tissues (from the same patient) using a tissue array containing cDNAs extracted from 68 samples taken from kidney, breast, prostate, uterus, ovary, cervix, colon, lung, stomach, rectum, small intestine, and from nine cancer cell lines. Differences in FOXP1 mRNA expression between normal and tumor samples were observed in 51% of cases. Most striking was the comparative loss of expression in 73% of colon tumors and comparative overexpression of FOXP1 mRNA in 75% of stomach tumors. Analysis of the FOXP1 mRNA expression in normal tissues (not taken from cancer patients) indicated that loss of FOXP1 expression may occur in some histologically normal tissues adjacent to tumors. Immunohistochemical analysis of FOXP1 protein expression was performed on 128 solid tumors, including 16 renal, 9 breast, 12 lung, 20 colon, 21 stomach, 10 head and neck, 35 prostate, and 5 pancreatic cases. Complete loss of expression, increased expression, and cytoplasmic mislocalization of the predominantly nuclear FOXP1 protein were frequently observed in neoplastic cells. Our study identifies FOXP1 as a new candidate tumor suppressor gene localized to the chromosome 3p14.1 region.

A new monoclonal antibody, GHI/61, which labels the majority of monocytes and tissue macrophages is described. This antibody recognizes an intracellular antigen of 130,000 MW (reduced) and 110,000 MW (unreduced). Using biochemical, flow cytometry and immunocytochemical studies antibody GHI/61 was shown to recognize the same antigen as the previously described antibodies Ber-MAC3, Ki-M8 and SM4. On the basis of the results obtained, antibodies GHI/61, SM4, Ber-MAC3 and Ki-M8 should form a new CD group at the next Leucocyte Typing Workshop. Since the antigen recognized by the antibody GHI/61 is relatively easy to purify, the sequencing and the isolation of the gene encoding this protein should be possible.