• Conditional Vascular Cell Adhesion Molecule 1 Deletion in Mice

      Koni, Pandelakis A.; Joshi, Sunil K.; Temann, Ulla-Angela; Olson, Dian; Burkly, Linda; Flavell, Richard A.; Institute of Molecular Medicine and Genetics; Department of Medicine (2001-03-19)
      We generated vascular cell adhesion molecule (VCAM)-1 “knock-in” mice and Cre recombinase transgenic mice to delete the VCAM-1 gene ( vcam-1 ) in whole mice, thereby overcoming the embryonic lethality seen with conventional vcam-1 –deficient mice. vcam-1 knock-in mice expressed normal levels of VCAM-1 but showed loss of VCAM-1 on endothelial and hematopoietic cells when interbred with a “TIE2Cre” transgene. Analysis of peripheral blood from conditional vcam-1– deficient mice revealed mild leukocytosis, including elevated immature B cell numbers. Conversely, the bone marrow (BM) had reduced immature B cell numbers, but normal numbers of pro-B cells. vcam-1 –deficient mice also had reduced mature IgD 1 B and T cells in BM and a greatly reduced capacity to support short-term migration of transferred B cells, CD4 1 T cells, CD8 1 T cells, and preactivated CD4 1 T cells to the BM. Thus, we report an until now unappreciated dominant role for VCAM-1 in lymphocyte homing to BM.
    • Exocytotic Insertion of Calcium Channels Constrains Compensatory Endocytosis to Sites of Exocytosis

      Smith, Robert M.; Baibakov, Boris; Ikebuchi, Yoshihide; White, Benjamin H.; Lambert, Nevin A.; Kaczmarek, Leonard K.; Vogel, Steven S.; Institute of Molecular Medicine and Genetics (2000-02-21)
      Proteins inserted into the cell surface by exocytosis are thought to be retrieved by compensatory endocytosis, suggesting that retrieval requires granule proteins. In sea urchin eggs, calcium influx through P-type calcium channels is required for retrieval, and the large size of sea urchin secretory granules permits the direct observation of retrieval. Here we demonstrate that retrieval is limited to sites of prior exocytosis. We tested whether channel distribution can account for the localization of retrieval at exocytotic sites. We find that P-channels reside on secretory granules before fertilization, and are translocated to the egg surface by exocytosis. Our study provides strong evidence that the transitory insertion of P-type calcium channels in the surface membrane plays an obligatory role in the mechanism coupling exocytosis and compensatory endocytosis.
    • A Kinetic Analysis of Calcium-Triggered Exocytosis

      Blank, Paul S.; Vogel, Steven S.; Malley, James D.; Zimmerberg, Joshua; Institute of Molecular Medicine and Genetics (2001-08-1)
      Although the relationship between exocytosis and calcium is fundamental both to synaptic and nonneuronal secretory function, analysis is problematic because of the temporal and spatial properties of calcium, and the fact that vesicle transport, priming, retrieval, and recycling are coupled. By analyzing the kinetics of sea urchin egg secretory vesicle exocytosis in vitro , the final steps of exocytosis are resolved. These steps are modeled as a three-state system: activated, committed, and fused, where interstate transitions are given by the probabilities that an active fusion complex commits (a ) and that a committed fusion complex results in fusion, p . The number of committed complexes per vesicle docking site is Poisson distributed with mean n. Experimentally, p and n increase with increasing calcium, whereas a and the p/n ratio remain constant, reducing the kinetic description to only one calcium-dependent, controlling variable, . On average, the calcium dependence of the maximum rate (R max ) and the time to reach R max (T peak ) are described by the calcium dependence of n . Thus, the nonlinear relationship between the free calcium concentration and the rate of exocytosis can be explained solely by the calcium dependence of the distribution of fusion complexes at vesicle docking sites.
    • Positive Selection of Cd4+ T Cells Is Induced in Vivo by Agonist and Inhibited by Antagonist Peptides

      Kraj, Piotr; Pacholczyk, Rafal; Ignatowicz, Hanna; Kisielow, Pawel; Jensen, Peter; Ignatowicz, Leszek; Institute of Molecular Medicine and Genetics (2001-08-20)
      The nature of peptides that positively select T cells in the thymus remains poorly defined. Here we report an in vivo model to study the mechanisms of positive selection of CD4+ T cells. We have restored positive selection of TCR transgenic CD4+ thymocytes, arrested at the CD4+CD8+ stage, due to the lack of the endogenously selecting peptide(s), in mice deficient for H2-M and invariant chain. A single injection of soluble agonist peptide(s) initiated positive selection of CD4+ transgenic T cells that lasted for up to 14 days. Positively selected CD4+ T cells repopulated peripheral lymphoid organs and could respond to the antigenic peptide. Furthermore, coinjection of the antagonist peptide significantly inhibited agonist-driven positive selection. Hence, contrary to the prevailing view, positive selection of CD4+ thymocytes can be induced in vivo by agonist peptides and may be a result of accumulation of signals from TCR engaged by different peptides bound to major histocompatibility complex class II molecules. We have also identified a candidate natural agonist peptide that induces positive selection of CD4+ TCR transgenic thymocytes.
    • Prenatal alcohol exposure triggers ceramide-induced apoptosis in neural crest-derived tissues concurrent with defective cranial development

      Wang, G; Bieberich, Erhard; Institute of Molecular Medicine and Genetics (2010-05-27)
      Fetal alcohol syndrome (FAS) is caused by maternal alcohol consumption during pregnancy. The reason why specific embryonic tissues are sensitive toward ethanol is not understood. We found that in neural crest-derived cell (NCC) cultures from the first branchial arch of E10 mouse embryos, incubation with ethanol increases the number of apoptotic cells by fivefold. Apoptotic cells stain intensely for ceramide, suggesting that ceramide-induced apoptosis mediates ethanol damage to NCCs. Apoptosis is reduced by incubation with CDP-choline (citicoline), a precursor for the conversion of ceramide to sphingomyelin. Consistent with NCC cultures, ethanol intubation of pregnant mice results in ceramide elevation and increased apoptosis of NCCs in vivo. Ethanol also increases the protein level of prostate apoptosis response 4 (PAR-4), a sensitizer to ceramide-induced apoptosis. Prenatal ethanol exposure is concurrent with malformation of parietal bones in 20% of embryos at day E18. Meninges, a tissue complex derived from NCCs, is disrupted and generates reduced levels of TGF-b1, a growth factor critical for bone and brain development. Ethanol-induced apoptosis of NCCs leading to defects in the meninges may explain the simultaneous presence of cranial bone malformation and cognitive retardation in FAS. In addition, our data suggest that treatment with CDP-choline may alleviate the tissue damage caused by alcohol.
    • T Cell Receptorâ Induced Calcineurin Activation Regulates T Helper Type 2 Cell Development by Modifying the Interleukin 4 Receptor Signaling Complex

      Yamashita, Masakatsu; Katsumata, Makoto; Iwashima, Makio; Kimura, Motoko; Shimizu, Chiori; Kamata, Tohru; Shin, Tahiro; Seki, Nobuo; Suzuki, Seiichi; Taniguchi, Masaru; et al. (2000-06-5)
      The activation of downstream signaling pathways of both T cell receptor (TCR) and interleukin 4 receptor (IL-4R) is essential for T helper type 2 (Th2) cell development, which is central to understanding immune responses against helminthic parasites and in allergic and autoimmune diseases. However, little is known about how these two distinct signaling pathways cooperate with each other to induce Th2 cells. Here, we show that successful Th2 cell development depends on the effectiveness of TCR-induced activation of calcineurin. An inhibitor of calcineurin activation, FK506, inhibited the in vitro anti-TCRâ induced Th2 cell generation in a dose-dependent manner. Furthermore, the development of Th2 cells was significantly impaired in naive T cells from dominant-negative calcineurin Aα transgenic mice, whereas that of Th1 cells was less affected. Efficient calcineurin activation in naive T cells upregulated Janus kinase (Jak)3 transcription and the amount of protein. The generation of Th2 cells induced in vitro by anti-TCR stimulation was inhibited significantly by the presence of Jak3 antisense oligonucleotides, suggesting that the Jak3 upregulation is an important event for the Th2 cell development. Interestingly, signal transducer and activator of transcription (STAT)5 became physically and functionally associated with the IL-4R in the anti-TCRâ activated developing Th2 cells that received efficient calcineurin activation, and also in established cloned Th2 cells. In either cell population, the inhibition of STAT5 activation resulted in a diminished IL-4â induced proliferation. Moreover, our results suggest that IL-4â induced STAT5 activation is required for the expansion process of developing Th2 cells. Thus, Th2 cell development is controlled by TCR-mediated activation of the Ca2+/calcineurin pathway, at least in part, by modifying the functional structure of the IL-4R signaling complex.
    • Viral Escape by Selection of Cytotoxic T Cellâ Resistant Variants in Influenza a Virus Pneumonia

      Price, Graeme E.; Ou, Rong; Jiang, Hong; Huang, Lei; Moskophidis, Demetrius; Institute of Molecular Medicine and Genetics (2000-06-5)
      Antigenic variation is a strategy exploited by influenza viruses to promote survival in the face of the host adaptive immune response and constitutes a major obstacle to efficient vaccine development. Thus, variation in the surface glycoproteins hemagglutinin and neuraminidase is reflected by changes in susceptibility to antibody neutralization. This has led to the current view that antibody-mediated selection of influenza A viruses constitutes the basis for annual influenza epidemics and periodic pandemics. However, infection with this virus elicits a vigorous protective CD8+ cytotoxic T lymphocyte (CTL) response, suggesting that CD8+ CTLs might exert selection pressure on the virus. Studies with influenza A virusâ infected transgenic mice bearing a T cell receptor (TCR) specific for viral nucleoprotein reveal that virus reemergence and persistence occurs weeks after the acute infection has apparently been controlled. The persisting virus is no longer recognized by CTLs, indicating that amino acid changes in the major viral nucleoprotein CTL epitope can be rapidly accumulated in vivo. These mutations lead to a total or partial loss of recognition by polyclonal CTLs by affecting presentation of viral peptide by class I major histocompatibility complex (MHC) molecules, or by interfering with TCR recognition of the mutant peptideâ MHC complex. These data illustrate the distinct features of pulmonary immunity in selection of CTL escape variants. The likelihood of emergence and the biological impact of CTL escape variants on the clinical outcome of influenza pneumonia in an immunocompetent host, which is relevant for the design of preventive vaccines against this and other respiratory viral infections, are discussed.