Imaging regulatory T cell dynamics and CTLA4-mediated suppression of T cell priming

Foxp3(+) regulatory T cells (Tregs) maintain immune homoeostasis through mechanisms that remain incompletely defined. Here by two-photon (2P) imaging, we examine the cellular dynamics of endogenous Tregs. Tregs are identified as two non-overlapping populations in the T-zone and follicular regions of the lymph node (LN). In the T-zone, Tregs migrate more rapidly than conventional T cells (Tconv), extend longer processes and interact with resident dendritic cells (DC) and Tconv. Tregs intercept immigrant DCs and interact with antigen-induced DC: Tconv clusters, while continuing to form contacts with activated Tconv. During antigen-specific responses, blocking CTLA4-B7 interactions reduces Treg-Tconv interaction times, increases the volume of DC: Tconv clusters and enhances subsequent Tconv proliferation in vivo. Our results demonstrate a role for altered cellular choreography of Tregs through CTLA4-based interactions to limit T-cell priming

SdiA, an N-Acylhomoserine Lactone Receptor, Becomes Active during the Transit of Salmonella enterica through the Gastrointestinal Tract of Turtles

encode a LuxR-type AHL receptor, SdiA, they cannot synthesize AHLs. In vitro, it is known that SdiA can detect AHLs produced by other bacterial species..We conclude that the normal gastrointestinal microbiota of most animal species do not produce AHLs of the correct type, in an appropriate location, or in sufficient quantities to activate SdiA. However, the results obtained with turtles represent the first demonstration of SdiA activity in animals

Detection and Tracking of T Cells in Time-lapse Imaging

The effective classification and tracking of cells obtained from modern staining techniques has significant limitations due to the necessity of having to train and utilize a human expert in the field who must manually identify each cell in each slide. Often times these slides are filled with noise cells that are not of particular interest to the researcher. The use of computational methods has the ability to effectively and efficiently enhance image quality, as well as identify and track target cell types over large data sets. Here we present a computational approach to the in vitro tracking of T cells in time-lapse imagery capable of scaling to hundreds of cells and applicable to multiple staining techniques

Orai1 Function is Essential for T Cell Homing to Lymph Nodes

In T lymphocytes, Ca2+ release-activated Ca2+ (CRAC) channels composed of Orai1 subunits trigger antigen-induced gene expression and cell proliferation through the NFAT pathway. We evaluated the requirement of CRAC channel function for lymphocyte homing using expression of a dominant-negative Orai1-E106A mutant to suppress Ca2+ signaling. To investigate homing and motility of human lymphocytes in immunocompromised mouse hosts, we transferred human lymphocytes either acutely or following stable engraftment after a second transfer from the same blood donor. Human and mouse lymphocyte homing was assessed and cells were tracked within lymph nodes by two-photon microscopy. Our results demonstrate that human T and B lymphocytes home into and migrate within the lymph nodes of immunocompromised NOD.SCID mice similar to murine lymphocytes. Human T and B cells colocalized in atrophied or reconstituted mouse lymph nodes, where T cells migrated in a random walk at velocities of 9-13 μm/min and B cells at 6 μm/min. Expression of Orai1-E106A inhibited CRAC channel function in human and mouse T cells and prevented homing from high endothelial venules into murine lymph nodes. Ca2+ signals induced by CCL21 were also inhibited in T cells expressing Orai1-E106A. With CRAC channels inhibited, the high-affinity form of LFA-1 failed to become active, and T cells failed to migrate across endothelial cells in a transwell model. These results establish a requirement for CRAC channel-mediated Ca2+ influx for T cell homing to lymph nodes mediated by high-affinity integrin activation and chemokine-induced transendothelial migration

Orai1 Function is Essential for T Cell Homing to Lymph Nodes

In T lymphocytes, Ca2+ release-activated Ca2+ (CRAC) channels composed of Orai1 subunits trigger antigen-induced gene expression and cell proliferation through the NFAT pathway. We evaluated the requirement of CRAC channel function for lymphocyte homing using expression of a dominant-negative Orai1-E106A mutant to suppress Ca2+ signaling. To investigate homing and motility of human lymphocytes in immunocompromised mouse hosts, we transferred human lymphocytes either acutely or following stable engraftment after a second transfer from the same blood donor. Human and mouse lymphocyte homing was assessed and cells were tracked within lymph nodes by two-photon microscopy. Our results demonstrate that human T and B lymphocytes home into and migrate within the lymph nodes of immunocompromised NOD.SCID mice similar to murine lymphocytes. Human T and B cells colocalized in atrophied or reconstituted mouse lymph nodes, where T cells migrated in a random walk at velocities of 9-13 μm/min and B cells at 6 μm/min. Expression of Orai1-E106A inhibited CRAC channel function in human and mouse T cells and prevented homing from high endothelial venules into murine lymph nodes. Ca2+ signals induced by CCL21 were also inhibited in T cells expressing Orai1-E106A. With CRAC channels inhibited, the high-affinity form of LFA-1 failed to become active, and T cells failed to migrate across endothelial cells in a transwell model. These results establish a requirement for CRAC channel-mediated Ca2+ influx for T cell homing to lymph nodes mediated by high-affinity integrin activation and chemokine-induced transendothelial migration

B cell TLR1/2, TLR4, TLR7 and TLR9 interact in induction of class switch DNA recombination: Modulation by BCR and CD40, and relevance to T-independent antibody responses

Ig class switch DNA recombination (CSR) in B cells is crucial to the maturation of antibody responses. It requires IgH germline IH-CH transcription and expression of AID, both of which are induced by engagement of CD40 or dual engagement of a Toll-like receptor (TLR) and B cell receptor (BCR). Here, we have addressed cross-regulation between two different TLRs or between a TLR and CD40 in CSR induction by using a B cell stimulation system involving lipopolysaccharides (LPS). LPS-mediated long-term primary class-switched antibody responses and memory-like antibody responses in vivo and induced generation of class-switched B cells and plasma cells in vitro. Consistent with the requirement for dual TLR and BCR engagement in CSR induction, LPS, which engages TLR4 through its lipid A moiety, triggered cytosolic Ca2+ flux in B cells through its BCR-engaging polysaccharidic moiety. In the presence of BCR crosslinking, LPS synergized with a TLR1/2 ligand (Pam3CSK4) in CSR induction, but much less efficiently with a TLR7 (R-848) or TLR9 (CpG) ligand. In the absence of BCR crosslinking, R-848 and CpG, which per se induced marginal CSR, virtually abrogated CSR to IgG1, IgG2a, IgG2b, IgG3 and/or IgA, as induced by LPS or CD154 (CD40 ligand) plus IL-4, IFN-γ or TGF-β, and reduced secretion of class-switched Igs, without affecting B cell proliferation or IgM expression. The CSR inhibition by TLR9 was associated with the reduction in AID expression and/or IgH germline IH-S-CH transcription, and required co-stimulation of B cells by CpG with LPS or CD154. Unexpectedly, B cells also failed to undergo CSR or plasma cell differentiation when co-stimulated by LPS and CD154. Overall, by addressing the interaction of TLR1/2, TLR4, TLR7 and TLR9 in the induction of CSR and modulation of TLR-dependent CSR by BCR and CD40, our study suggests the complexity of how different stimuli cross-regulate an important B cell differentiation process and an important role of TLRs in inducing effective T-independent antibody responses to microbial pathogens, allergens and vaccines

Toll-like receptor 4-activated B cells out-compete Toll-like receptor 9-activated B cells to establish peripheral immunological tolerance

B-cell–induced peripheral T-cell tolerance is characterized by suppression of T-cell proliferation and T-cell–dependent antibody production. However, the cellular interactions that underlie tolerance induction have not been identified. Using two-photon microscopy of lymph nodes we show that tolerogenic LPS-activated membrane-bound ovalbumin (mOVA) B cells (LPS B cells) establish long-lived, highly motile conjugate pairs with responding antigen-specific OTII T cells but not with antigen-irrelevant T cells. Treatment with anti–CTLA-4 disrupts persistent B-cell–T-cell (B–T) contacts and suppresses antigen-specific tolerance. Nontolerogenic CpG-activated mOVA B cells (CpG B cells) also form prolonged, motile conjugates with responding OTII T cells when transferred separately. However, when both tolerogenic and nontolerogenic B-cell populations are present, LPS B cells suppress long-lived CpG B–OTII T-cell interactions and exhibit tolerogenic dominance. Contact of LPS B cells with previously established B–T pairs resulted in partner-swapping events in which LPS B cells preferentially migrate toward and disrupt nontolerogenic CpG mOVA B-cell–OTII T-cell pairs. Our results demonstrate that establishment of peripheral T-cell tolerance involves physical engagement of B cells with the responding T-cell population, acting in a directed and competitive manner to alter the functional outcome of B–T interactions

Two-photon Imaging of Cellular Dynamics in the Mouse Spinal Cord

Two-photon (2P) microscopy is utilized to reveal cellular dynamics and interactions deep within living, intact tissues. Here, we present a method for live-cell imaging in the murine spinal cord. This technique is uniquely suited to analyze neural precursor cell (NPC) dynamics following transplantation into spinal cords undergoing neuroinflammatory demyelinating disorders. NPCs migrate to sites of axonal damage, proliferate, differentiate into oligodendrocytes, and participate in direct remyelination. NPCs are thereby a promising therapeutic treatment to ameliorate chronic demyelinating diseases. Because transplanted NPCs migrate to the damaged areas on the ventral side of the spinal cord, traditional intravital 2P imaging is impossible, and only information on static interactions was previously available using histochemical staining approaches. Although this method was generated to image transplanted NPCs in the ventral spinal cord, it can be applied to numerous studies of transplanted and endogenous cells throughout the entire spinal cord. In this article, we demonstrate the preparation and imaging of a spinal cord with enhanced yellow fluorescent protein-expressing axons and enhanced green fluorescent protein-expressing transplanted NPCs