Paul C. Cheng

The CD19/CD21 Complex Functions to Prolong B Cell Antigen Receptor Signaling from Lipid Rafts

The CD19/CD21 complex functions to significantly enhance B cell antigen receptor (BCR) signaling in response to complement-tagged antigens. Recent studies showed that following antigen binding the BCR translocates into plasma membrane lipid rafts that serve as platforms for BCR signaling. Here, we show that the binding of complement-tagged antigens stimulates the translocation of both the BCR and the CD19/CD21 complex into lipid rafts, resulting in prolonged residency in and signaling from the rafts, as compared to BCR cross-linking alone. When coligated to the BCR, the CD19/CD21 complex retards the internalization and degradation of the BCR. The colocalization and stabilization of the BCR and the CD19/CD21 complex in plasma membrane lipid rafts represents a novel mechanism by which a coreceptor enhances BCR signaling.

The Role of the CD19/CD21 Complex in B Cell Processing and Presentation of Complement-Tagged Antigens

The CD19/CD21 complex is an essential B cell coreceptor that functions synergistically to enhance signaling through the B cell Ag receptor in response to T cell-dependent, complement-tagged Ags. In this study, we use a recombinant protein containing three tandemly arranged copies of C3d and the Ag hen egg lysozyme, shown to be a highly effective immunogen in vivo, to evaluate the role of the CD19/CD21 complex in Ag processing in B cells. Evidence is provided that coengagement of the CD19/CD21 complex results in more rapid and efficient production of antigenic peptide/class II complexes as compared with B cell Ag receptor-mediated processing alone. The CD19/CD21 complex does not itself target complement-tagged Ags for processing, but rather appears to influence B cell Ag processing through its signaling function. The ability of the CD19/CD21 complex to augment processing may be an important element of the mechanism by which the CD19/CD21 complex functions to promote B cell responses to T cell-dependent complement-tagged Ags in vivo.

Translocation of the B Cell Antigen Receptor into Lipid Rafts Reveals a Novel Step in Signaling

The cross-linking of the B cell Ag receptor (BCR) leads to the initiation of a signal transduction cascade in which the earliest events involve the phosphorylation of the immunoreceptor tyrosine-based activation motifs of Igα and Igβ by the Src family kinase Lyn and association of the BCR with the actin cytoskeleton. However, the mechanism by which BCR cross-linking initiates the cascade remains obscure. In this study, using various A20-transfected cell lines, biochemical and genetic evidence is provided that BCR cross-linking leads to the translocation of the BCR into cholesterol- and sphingolipid-rich lipid rafts in a process that is independent of the initiation of BCR signaling and does not require the actin cytoskeleton. Translocation of the BCR into lipid rafts did not require the Igα/Igβ signaling complex, was not dependent on engagement of the FcR, and was not blocked by the Src family kinase inhibitor PP2 or the actin-depolymerizing agents cytochalasin D or latrunculin. Thus, cross-linking or oligomerization of the BCR induces the BCR translocation into lipid rafts, defining an event in B cell activation that precedes receptor phosphorylation and association with the actin cytoskeleton.

Honey bee propolis: prospects in medicine.

Modern physicians trained in allopathic medicine are usually wary of naturopathic remedies because the mechanisms of efficacy are usually unclear. Indeed, if one examines recipes from Chinese herbal medicine or some ‘home remedies,’ the active ingredients are unknown. Also, demonstration of the effectiveness of the remedies often is not scientific (no use of placebos), and could be a result of psychological effects of the patient. However, modern allopathic doctors and researchers should not ignore potential benefits which natural products may provide in curing some of the most serious medical problems today.

Macrophage PTEN Regulates Expression and Secretion of Arginase I Modulating Innate and Adaptive Immune Responses

The activation of innate immune cells triggers numerous intracellular signaling pathways, which require tight control to mount an adequate immune response. The PI3K signaling pathway is intricately involved in innate immunity, and its activation dampens the expression and release of proinflammatory cytokines in myeloid cells. These signaling processes are strictly regulated by the PI3K antagonist, the lipid phosphatase, PTEN, a known tumor suppressor. Importantly, PTEN is responsible for the elevated production of cytokines such as IL-6 in response to TLR agonists, and deletion of PTEN results in diminished inflammatory responses. However, the mechanisms by which PI3K negatively regulates TLR signaling are only partially resolved. We observed that Arginase I expression and secretion were markedly induced by PTEN deletion, suggesting PTEN−/− macrophages were alternatively activated. This was mediated by increased expression and activation of the transcription factors C/EBPβ and STAT3. Genetic and pharmacologic experimental approaches in vitro, as well as in vivo autoimmunity models, provide convincing evidence that PI3K/PTEN-regulated extracellular Arginase I acts as a paracrine regulator of inflammation and immunity.

A Role for MHC Class II Antigen Processing in B Cell Development

For mature B cells, the encounter with foreign antigen results in the selective expansion of the cells and their differentiation into antibody secreting cells or memory B cells. The response of mature B cells to antigen requires not only antigen binding to and signaling through the B cell antigen receptor (BCR) but also the processing and presentation of the BCR bound antigen to helper T cells. Thus, in mature B cells, the ability to process and present antigen to helper T cells plays a critical role in determining the outcome of antigen encounter. In immature B cells, the binding of antigen results in negative selection of the B cell, inducing apoptosis, anergy or receptor editing. Negative selection of immature B cells requires antigen induced signaling through the BCR, analogous to the signaling function of the BCR in mature B cells. However, the role of class II antigen processing and presentation in immature B cells is less well understood. Current evidence indicates that the ability to process and present antigen bound to the BCR is a late acquisition of developing B cells, suggesting that during negative selection B cells may not present BCR bound antigen and interact with helper T cells However, the expression of class II molecules is an early acquisition of B cells and recent evidence indicates that the expression of class II molecules early in development is required for the generation of long lived mature B cells. Here we review our current understanding of the processing and presentation of antigen by mature B cells and the role for antigen processing and class II expression during B cell development.

A1.03 Arginase I and osteoclastogenesis

Background and objectives Osteoclasts are giant, multi-nucleated cells that derive from the monocyte-macrophage linage and are involved in bone turnover. They are further known as the main effector cells for development of age-related osteoporosis. While the role of Arginase I within certain myeloid lineages such as macrophages is well appreciated, its role within osteoclasts is relatively unknown. Our aim was therefore to investigate the importance of the enzyme in the context of osteoclastogenesis. Materials and methods We analysed osteoclastogenesis of C57BL/6J or BALB/c wildtype cells in vitro in the presence and absence of recombinant Arginase I (recARG1) and its inhibitor nor-NOHA. This was complemented via qPCR analysis of marker genes. We further investigated the potential of the enzyme to induce cell death via flow cytometry analysis of 7-AAD and Annexin V. Results In osteoclast differentiation assays, we show that Arginase I is strongly downregulated during osteoclastogenesis, suggesting involvement of this enzyme in OC differentiation. We further show that addition of recArgI completely abolishes osteoclast formation without inducing cell death. The inhibitory effect of recArgI on osteoclastogenesis was completely dependent on the enzymatic function, as no decrease in osteoclast formation could be observed during combined addition of recArgI and its specific inhibitor nor-NOHA. We further demonstrate that recArgI specifically inhibits RANKL-mediated terminal differentiation of OCs, but has no effect on MCSF dependent generation of OC precursors. In line, we could show that addition of recombinant Arginase I negatively regulated the expression of classic RANKL induced osteoclastic marker genes such as TRAP and Cathepsin K. Conclusions We propose that recArgI might be a potent inhibitor of osteoclastogenesis and could prove itself to be useful for the treatment of osteoclast driven diseases, such as osteoporosis.