The immune synapses reveal aberrant functions of CD8 T cells during chronic HIV infection.

Chronic HIV infection causes persistent low-grade inflammation that induces premature aging of the immune system including senescence of memory and effector CD8 T cells. To uncover the reasons of gradually diminished potency of CD8 T cells from people living with HIV, here we expose the T cells to planar lipid bilayers containing ligands for T-cell receptor and a T-cell integrins and analyze the cellular morphology, dynamics of synaptic interface formation and patterns of the cellular degranulation. We find a large fraction of phenotypically naive T cells from chronically infected people are capable to form mature synapse with focused degranulation, a signature of a differentiated T cells. Further, differentiation of aberrant naive T cells may lead to the development of anomalous effector T cells undermining their capacity to control HIV and other pathogens that could be contained otherwise.

Assessment of the Synaptic Interface of Primary Human T Cells from Peripheral Blood and Lymphoid Tissue.

The current understanding of the dynamics and structural features of T-cell synaptic interfaces has been largely determined through the use of glass-supported planar bilayers and in vitro-derived T-cell clones or lines1,2,3,4. How these findings apply to the primary human T cells isolated from blood or lymphoid tissues is not known, partly due to significant difficulties in obtaining a sufficient number of cells for analysis5. Here we address this through the development of a technique exploiting multichannel flow slides to build planar lipid bilayers containing activating and adhesion molecules. The low height of the flow slides promotes rapid cell sedimentation in order to synchronize cell:bilayer attachment, thereby allowing researchers to study the dynamic of the synaptic interface formation and the kinetics of the granules release. We apply this approach to analyze the synaptic interface of as few as 104 to 105 primary cryopreserved T cells isolated from lymph nodes (LN) and peripheral blood (PB). The results reveal that the novel planar lipid bilayer technique enables the study of the biophysical properties of primary human T cells derived from blood and tissues in the context of health and disease.

Limited immune surveillance in lymphoid tissue by cytolytic CD4+ T cells during health and HIV disease.

CD4+ T cells subsets have a wide range of important helper and regulatory functions in the immune system. Several studies have specifically suggested that circulating effector CD4+ T cells may play a direct role in control of HIV replication through cytolytic activity or autocrine ß-chemokine production. However, it remains unclear whether effector CD4+ T cells expressing cytolytic molecules and ß-chemokines are present within lymph nodes (LNs), a major site of HIV replication. Here, we report that expression of ß-chemokines and cytolytic molecules are enriched within a CD4+ T cell population with high levels of the T-box transcription factors T-bet and eomesodermin (Eomes). This effector population is predominately found in peripheral blood and is limited in LNs regardless of HIV infection or treatment status. As a result, CD4+ T cells generally lack effector functions in LNs, including cytolytic capacity and IFNγ and ß-chemokine expression, even in HIV elite controllers and during acute/early HIV infection. While we do find the presence of degranulating CD4+ T cells in LNs, these cells do not bear functional or transcriptional effector T cell properties and are inherently poor to form stable immunological synapses compared to their peripheral blood counterparts. We demonstrate that CD4+ T cell cytolytic function, phenotype, and programming in the peripheral blood is dissociated from those characteristics found in lymphoid tissues. Together, these data challenge our current models based on blood and suggest spatially and temporally dissociated mechanisms of viral control in lymphoid tissues.

Integrins Influence the Size and Dynamics of Signaling Microclusters in a Pyk2-dependent Manner.

Integrin engagement on lymphocytes initiates "outside-in" signaling that is required for cytoskeleton remodeling and the formation of the synaptic interface. However, the mechanism by which the "outside-in" signal contributes to receptor-mediated intracellular signaling that regulates the kinetics of granule delivery and efficiency of cytolytic activity is not well understood. We have found that variations in ICAM-1 expression on tumor cells influence killing kinetics of these cells by CD16.NK-92 cytolytic effectors suggesting that changes in integrin ligation on the effector cells regulate the kinetics of cytolytic activity by the effector cells. To understand how variations of the integrin receptor ligation may alter cytolytic activity of CD16.NK-92 cells, we analyzed molecular events at the contact area of these cells exposed to planar lipid bilayers that display integrin ligands at different densities and activating CD16-specific antibodies. Changes in the extent of integrin ligation on CD16.NK-92 cells at the cell/bilayer interface revealed that the integrin signal influences the size and the dynamics of activating receptor microclusters in a Pyk2-dependent manner. Integrin-mediated changes of the intracellular signaling significantly affected the kinetics of degranulation of CD16.NK-92 cells providing evidence that integrins regulate the rate of target cell destruction in antibody-dependent cell cytotoxicity (ADCC).

Integrin receptors on tumor cells facilitate NK cell-mediated antibody-dependent cytotoxicity.

NK cells that mediate ADCC play an important role in tumor-specific immunity. We have examined factors limiting specific lysis of tumor cells by CD16.NK-92 cells induced by CNTO 95LF antibodies recognizing αV integrins that are overexpressed on many tumor cells. Although all tested tumor cells were killed by CD16.NK-92 effectors in the presence of the antibodies, the killing of target cells with a low level of ICAM-1 expression revealed a dramatic decrease in their specific lysis at high antibody concentration, revealing a dose limiting effect. A similar effect was also observed with primary human NK cells. The effect was erased after IFN-γ treatment of tumor cells resulting in upregulation of ICAM-1. Furthermore, killing of the same tumor cells induced by Herceptin antibody was significantly impaired in the presence of CNTO 95Ala-Ala antibody variant that blocks αV integrins but is incapable of binding to CD16. These data suggest that αV integrins on tumor cells could compensate for the loss of ICAM-1 molecules, thereby facilitating ADCC by NK cells. Thus, NK cells could exercise cytolytic activity against ICAM-1 deficient tumor cells in the absence of proinflammatory cytokines, emphasizing the importance of NK cells in tumor-specific immunity at early stages of cancer.

The structure of helix 89 of 23S rRNA is important for peptidyl transferase function of Escherichia coli ribosome.

Helix 89 of the 23S rRNA connects ribosomal peptidyltransferase center and elongation factor binding site. Secondary structure of helix 89 determined by X-ray structural analysis involves less base pairs then could be drawn for the helix of the same primary structure. It can be that alternative secondary structure might be realized at some stage of translation. Here by means of site-directed mutagenesis we stabilized either the "X-ray" structure or the structure with largest number of paired nucleotides. Mutation UU2492-3C which aimed to provide maximal pairing of the helix 89 of the 23S rRNA was lethal. Mutant ribosomes were unable to catalyze peptide transfer independently either with aminoacyl-tRNA or puromycin.

Mutations at the accommodation gate of the ribosome impair RF2-dependent translation termination.

During protein synthesis, aminoacyl-tRNA (aa-tRNA) and release factors 1 and 2 (RF1 and RF2) have to bind at the catalytic center of the ribosome on the 50S subunit where they take part in peptide bond formation or peptidyl-tRNA hydrolysis, respectively. Computer simulations of aa-tRNA movement into the catalytic site (accommodation) suggested that three nucleotides of 23S rRNA, U2492, C2556, and C2573, form a "gate" at which aa-tRNA movement into the A site is retarded. Here we examined the role of nucleotides C2573 of 23S rRNA, a part of the putative accommodation gate, and of the neighboring A2572 for aa-tRNA binding followed by peptide bond formation and for the RF2-dependent peptide release. Mutations at the two positions did not affect aa-tRNA accommodation, peptide bond formation, or the fidelity of aa-tRNA selection, but impaired RF2-catalyzed peptide release. The data suggest that the ribosome is a robust machine that allows rapid aa-tRNA accommodation despite the defects at the accommodation gate. In comparison, peptide release by RF2 appears more sensitive to these mutations, due to slower accommodation of the factor or effects on RF2 positioning in the A site.