Further, we suggest a possible role of tumor-expressed FcRI in complementing the metastatic phenotype. Open in a separate window Figure 6 Model of specific Ab-tumor cell promotion. kinase signal transduction pathway. A selective inhibitor of phosphatidylinositol-3 kinase also inhibited this induction of tumor cell proliferation. These findings support a role for immune complexes and FcRI expression by tumor cells in augmentation of tumor growth and a metastatic phenotype. test. Results B Cells with Prior Exposure to Tumor-Associated Antigens Promoted In Vivo Tumor Growth To investigate whether B cells first require exposure to tumor-associated antigens to be able to interact with tumors in promoting tumor growth compared with no exogenous B cells (as a control), and to B cells isolated from spleens of non-tumor-bearing mice spleen (N-SpBL) having comparable scores compared with the control (Physique 1compared with B cells isolated from spleens of non-tumor-bearing mice (N-SpBL) (Physique 1culture, forming soluble immune complexes with the secreted sTn-mucin. Proliferation was then compared between T-47D tumor cells incubated in various concentrations of anti-sTn IgG1 mAb, and control T-47D tumor cells incubated with serum-free medium only. A statistically significant induction of tumor cell growth was observed for the tumor cells incubated with anti-sTn IgG1 mAb compared with the control tumor cells (Physique 3assay using murine metastatic melanoma cells, B16F1. We have found that these melanoma cells also express FcRI, but do not secrete detectable amounts of sTn-mucin. The melanoma cells were treated in culture with either anti-sTn IgG1 mAb in various concentrations and Nav1.7-IN-2 supernatant made up of sTn-mucin, with anti-sTn IgG1 mAb, or with fresh tissue culture medium as a control. A statistically significant induction of tumor cell growth was observed for the melanoma cells incubated with anti-sTn IgG1 mAb and sTn-mucin compared with melanoma cells incubated in either anti-sTn IgG1 mAb or no antibody (Physique 3is associated with the metastatic potential of the tumor [14,15], may be used as a marker of progression and metastasis [15], and may be used as a prognostic indicator [16]. To investigate if cross-linking of FcRI expressed by sTn-mucin-secreting tumor cells may also induce sTn-mucin production, T-47D tumor cells were incubated in the presence of either various concentrations of anti-sTn IgG1 mAb, tissue culture medium alone, or an isotype control mAb. The culture supernatants Cdc14A1 were then assayed for sTn-mucin production by measuring the amount of sTn epitope, and sTn-mucin production was then expressed as the ratio of the amount of sTn-mucin to the amount Nav1.7-IN-2 of cell proliferation to take induction of cell proliferation into account. sTn-mucin production by T-47D tumor cells in the presence of anti-sTn IgG1 mAb was increased approximately two-fold over comparative cells to which isotype control mAb was added (Physique 4). Further, treatment of T-47D tumor cells with an isotype control mAb did not induce a detectable increase in sTn-mucin production compared with the comparative control cells to which no IgG1 mAb was added (not shown). Based on these results, in addition to being a mechanism by which tumor cell proliferation is usually induced, immune complexes formed between sTn-mucin and anti-sTn Ab can induce production of sTn-mucin by sTn-mucin-secreting, Fcexperiments show that B cells exposed to tumor-associated antigens can promote tumor growth in immune-competent animals, sustaining the suggestion of an undesired tumor promoting role of a humoral immune response induced by tumor [5C7]. Moreover, the results of the experiments, utilizing a model that isolated the conversation to only tumor cells and B cells, stress the concept that B cells exposed to tumor-associated antigens can directly interact with certain tumor cells through specific recognition, and promote tumor cell growth. As shown by flow cytometry tumor cells can express FcRI. RT-PCR and DNA sequencing showed that those tumor cells expressed FcRIB-RNA, which encodes a transmembrane receptor with two extracellular domains, in which the second extracellular domain name splices precisely to the transmembrane/cytoplasmic domain name, and does not utilize the third extra-cellular domain name encoded by the FcRIA gene [11]. FcRIB has higher affinity for immune complexes than free Ab [13]; this suggests that an specific recognition tumor cell/B cells Nav1.7-IN-2 could be carried out, in some cases, by immune complexes produced by binding of tumor cell-secreted antigens with the correspondent antibodies produced by the lymphocytes. The experiments with adenocarcinoma cells secreting sTn-mucin incubated in the presence of anti-sTn monoclonal Ab sustain the interpretation that tumor-associated antigen secreted by tumor cells,.