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B cell-specific gene ablation of Notch2 results in the loss of the marginal zone (MZ) B-cell lineage. To analyze the effects of constitutive Notch2 signaling in B cells, we have generated a transgenic mouse strain that allows the conditional expression of a constitutively active, intracellular form of Notch2 (Notch2IC). Expression of Notch2IC at the earliest developmental stages of the B-cell lineage completely abolished B-cell generation and led to the development of ectopic T cells in the bone marrow (BM), showing that Notch2IC is acting redundantly with Notch1IC in driving ectopic T-cell differentiation. In B cells clearly committed to the B-cell lineage induction of Notch2IC drove all cells toward the MZ B-cell compartment at the expense of follicular B cells. Notch2IC-expressing B cells reflected the phenotype of wild-type MZ B cells for their localization in the MZ, the expression of characteristic surface markers, their enhanced proliferation after stimulation, and increased basal activity of Akt, Erk, and Jnk. Notch2IC-driven MZ B-cell generation in the spleen was achieved even in the absence of CD19. Our results implicate that a constitutive Notch2 signal in transitional type 1 B cells is sufficient to drive MZ B-cell differentiation.

The ubiquitin-editing enzyme A20/TNFAIP3 is essential for controlling signals inducing the activation of nuclear factor-κB transcription factors. Polymorphisms and mutations in the TNFAIP3 gene are linked to various human autoimmune conditions, and inactivation of A20 is a frequent event in human B-cell lymphomas characterized by constitutive nuclear factor-κB activity. Through B cell-specific ablation in the mouse, we show here that A20 is required for the normal differentiation of the marginal zone B and B1 cell subsets. However, loss of A20 in B cells lowers their activation threshold and enhances proliferation and survival in a gene-dose-dependent fashion. Through the expression of proinflammatory cytokines, most notably interleukin-6, A20-deficient B cells trigger a progressive inflammatory reaction in naive mice characterized by the expansion of myeloid cells, effector-type T cells, and regulatory T cells. This culminates in old mice in an autoimmune syndrome characterized by splenomegaly, plasma cell hyperplasia, and the presence of class-switched, tissue-specific autoantibodies.

Chronic administration of nicotine is followed by a general stimulation of brain metabolism that results in a distinct increase of glucose transport protein densities for Glut1 and Glu3, and local cerebral glucose utilization (LCGU). This increase of LCGU might be paralleled by an enhanced production of lactate. Therefore, the question arose as to whether chronic nicotine infusion is accompanied by increased local densities of monocarboxylate transporter MCT1 in the brain. Secondly, we inquired whether LCGU might be correlated with local densities of MCT1 during normal conditions and after chronic nicotine infusion. Nicotine was given subcutaneously for 1 week by osmotic mini-pumps and local densities of MCT1 were measured by immunoautoradiographic methods in cryosections of rat brains. MCT1 density was significantly increased in 21 of 32 brain structures investigated (median increase 15.0+/-3.6%). Immunohistochemical stainings of these substructures revealed an over-expression of MCT1 within endothelial cells and astrocytes of treated animals. A comparison of 23 MCT1 densities with LCGU measured in the same structures in a previous study revealed a partial correlation between both parameters under control conditions and after chronic nicotine infusion. 10 out of 23 brain areas, which showed a significant increase of MCT1 density due to chronic nicotine infusion, also showed a significant increase of LCGU. In summary, our data show that chronic nicotine infusion induces a moderate increase of local and global density of MCT1 in defined brain structures. However, in terms of brain topologies and substructures this phenomenon did partially match with increased LCGU. It is concluded that MCT1 transporters were upregulated during chronic nicotine infusion at the level of brain substructures and, at least partially, independently of LCGU.

Screening of head and neck carcinoma patients with the proteomics-based AMIDA technology yielded a set of tumour-associated antigens, including the intermediate filament protein cytokeratin 8 (CK8). The expression pattern and specificity of CK8 was compared with those of the established markers pan-cytokeratins and CK13, and with that of the proliferation marker Ki67. Expression of CK8 correlated positively with malignancies of the head and neck areas. CK8 was not expressed in healthy epithelium, except for some rare cases of cells of the basal layer and laryngeal tissue. In contrast, the vast majority of head and neck squamous cell carcinomas and metastases strongly expressed CK8. Interestingly, CK8 de novo expression correlated with dysplastic areas of oral leukoplakic lesions, while hyperplastic leukoplakia remained CK8-negative but strongly panCK and CK13 positive. Thus, CK8 is an attractive marker molecule for a differentiated diagnosis of leukoplakia and head and neck carcinomas, which possesses notedly improved specificity as compared with panCK and CK13.

We reported the identification of tumour-associated antigens from head and neck carcinomas, including cytokeratin 8 (CK8). These antigens were isolated based on the humoral immune response they elicit in vivo using the antibody-mediated identification of antigens technology. Unlike healthy squamous epithelium, tumour cells displayed CK8 at the plasma membrane. However, the actual presence of CK8 at the plasma membrane is still a matter of debate. Here, we have analyzed the expression of CK8 in detail using confocal laser scanning microscopy and circumstantiated its localization at the plasma membrane of carcinoma cells. Healthy human tissues were devoid of CK8 at the membrane, with the exception of hepatocytes. Moreover, membrane-associated CK8 molecules experienced a re-distribution throughout mitosis, which was associated with phosphorylation at serine 73. Phosphorylated CK8 redistributed into dense speckles and relocated to the plasma membrane upon cytokinesis. Thus, CK8 possesses genuine extracellular epitopes on tumour cells, which may represent valuable targets for therapy.

Recently, we described a new target-identification technology, autoantibody-mediated identification of antigens (AMIDA). AMIDA takes advantage of autologous serum autoantibodies to identify disease-associated antigens. Here, we evaluated the allogenic variant of AMIDA (allo-AMIDA), using permanent cancer cell lines as an antigen-pool rather than primary biopsy samples. Twelve different proteins were retrieved exclusively with antibodies from cancer patients, but not from healthy donors. The expression of three of these antigens, e-FABP, hnRNP H, and Grb2, was evaluated in more detail. All three proteins were strongly overexpressed in primary carcinomas and metastases thereof, as compared to healthy epithelium. Additionally, serum reactivity against e-FABP was detected in 20% of cancer patients but only 2% of healthy volunteers. In summary, we demonstrate that permanent cancer cell lines represent a reliable source for tumour-associated antigens. Moreover, we show that allo-AMIDA is suitable for the identification of tumour-specific antigens overcoming the limitations of autologous screening techniques., (Copyright 2004 Elsevier Inc.)