Apoptosis occurs predominantly in bystander cells and not in productively infected cells of HIV- and SIV-infected lymph nodes.

Although 13 years have passed since identification of human immunodeficiency virus-1 (HIV-1) as the cause of AIDS, we do not yet know how HIV kills its primary target, the T cell that carries the CD4 antigen. We and others have shown an increase in the percentage of apoptotic cells among circulating CD4+ (and CD8+) T cells of HIV-seropositive individuals and an increase in frequency of apoptosis with disease progression. However, it is not known if this apoptosis occurs in infected or uninfected T cells. We show here, using in situ labelling of lymph nodes from HIV-infected children and SIV-infected macaques, that apoptosis occurs predominantly in bystander cells and not in the productively infected cells themselves. These data have implications for pathogenesis and therapy, namely, arguing that rational drug therapy may involve combination agents targeting viral replication in infected cells and apoptosis of uninfected cells.

Small splenic B cells that bind to antigen-specific T helper (Th) cells and face the site of cytokine production in the Th cells selectively proliferate: immunofluorescence microscopic studies of Th-B antigen-presenting cell interactions.

Antigen (Ag)-specific T helper (Th) cells regulate the proliferation and differentiation of Ag-specific B cells by secreting cytokines and by expressing activating receptors like gp39. In vitro, the cytokines and the activating receptors function in an Ag-nonspecific manner. It is unclear, therefore, how Ag specificity is imposed on B cell responses in physiological Th-B cell interactions. Here we studied, at the single cell level, the interactions between cloned Th cells and small splenic B cells, which served as Ag-specific antigen-presenting cells (APCs) to the Th cells. Digital confocal immunofluorescence microscopy of Th-B cell conjugates revealed significant variability in the molecular and cellular properties of these interactions, in spite of the fact that all the interactions in this system were expected to be Ag specific. After 30 h of incubation B cells began to divide, and this process was entirely dependent on the presence of both Th cells and Ag. Immunofluorescence microscopic studies showed that essentially all the mitotic B cells were bound to Th cells and faced the microtubule organizing center (MTOC) in the Th cells where interleukin 4 was highly concentrated. Other B cells that were bound to the same Th cells but were not close to the Th-MTOC remained in interphase. These results provide the first direct structural and functional evidence that the site of interaction of B cells with Th cells affects their immune response. We propose that, during Ag-induced Th-B cell interactions, B cells that are bound facing the Th-MTOC proliferate preferentially because they are the recipients of locally secreted cytokines. In addition, these B cells may interact with newly expressed receptors, which may also be locally inserted into the Th membrane. The polarized delivery of activating molecules towards the Th-bound APCs may impose functional specificity on effector molecules that otherwise are not Ag specific.

Physical Dating Violence in Spain and the United Kingdom and the Importance of Relationship Quality.

Mixed-gender friendships, romantic relationships, and sexual behaviors increase during adolescence as a normal part of development. However, some studies have revealed potential risks to these types of social relationships. Different authors have indicated that dating violence among adolescents is an issue for concern. To date, there has been little research on this topic cross-nationally. This study examined and compared the prevalence and characteristics of physical dating violence among young people aged between 15 and 18 years in England and Spain (N = 200 in Spain, N = 199 in England), and how being involved (or not) in this violence relates to romantic relationship quality. Results indicated that approximately 23% of young people reported victimization and 30% reported perpetrating physical dating violence. In both countries, most of those involved in physical dating violence reported involvement in reciprocal violence (displaying both aggression and victimization). Those young people involved in dating violence reported higher levels on scales assessing negative aspects of relationship quality compared with those not involved, but there were no significant differences in positive aspects of relationship quality. Furthermore, different patterns appeared relating to the severity of violence and country. The findings are discussed in terms of their implications for theory and practice.

Selective modulation of protein kinase C-theta during T-cell activation.

Every cell contains many families of protein kinases, and may express several structurally related yet genetically distinct kinases of each family. The activity of the serine/threonine protein kinase C (PKC) enzymes has long been implicated in T-cell activation, but it is not known which members of the PKC family regulate the T-cell response to foreign antigens. The activation of T cells by antigen-presenting cells (APCs) is spatially restricted to their site of contact, where receptors on the T cells engage their counter-receptors on the APCs. We used this localized engagement to identify, at the single-cell level, intracellular proteins involved in the activation process. By digital immunofluorescence microscopy, we localized six isoforms of PKC in antigen-specific T-cell clones activated by APCs. Surprisingly, only PKC-theta translocated to the site of cell contact. Accordingly, in vitro kinase activity assays of PKC immunoprecipitates from the conjugates of T cells and APCs showed a selective increase in the activity of PKC-theta, indicating that the translocated enzyme is active. Several modes of partial T-cell activation that failed to cause PKC-theta translocation also failed to cause T-cell proliferation, further suggesting the involvement of PKC-theta in T-cell activation.

Three-dimensional segregation of supramolecular activation clusters in T cells.

Activation of T cells by antigen-presenting cells (APCs) depends on the complex integration of signals that are delivered by multiple antigen receptors. Most receptor-proximal activation events in T cells were identified using multivalent anti-receptor antibodies, eliminating the need to use the more complex APCs. As the physiological membrane-associated ligands on the APC and the activating antibodies probably trigger the same biochemical pathways, it is unknown why the antibodies, even at saturating concentrations, fail to trigger some of the physiological T-cell responses. Here we study, at the level of the single cell, the responses of T cells to native ligands. We used a digital imaging system and analysed the three-dimensional distribution of receptors and intracellular proteins that cluster at the contacts between T cells and APCs during antigen-specific interactions. Surprisingly, instead of showing uniform oligomerization, these proteins clustered into segregated three-dimensional domains within the cell contacts. The antigen-specific formation of these new, spatially segregated supramolecular activation clusters may generate appropriate physiological responses and may explain the high sensitivity of the T cells to antigen.

Live cell fluorescence imaging of T cell MEKK2: redistribution and activation in response to antigen stimulation of the T cell receptor.

T cell activation requires engagement of the T cell receptor (TCR) at the interface of conjugates formed with antigen-presenting cells. TCR engagement is accompanied by a redistribution of specific signaling molecules to the cytoplasmic region of the TCR complex. In this study, immunocytochemistry and live cell fluorescence imaging demonstrate that T cell MEK kinase 2 (MEKK2) is translocated to the T cell/antigen-presenting cell interface in response to antigen activation. MEKK2 translocation occurs more rapidly as the antigen concentration is increased. Biochemical activation of MEKK2 follows TCR stimulation, and expression of a dominant-negative MEKK2 inhibits TCR-mediated conjugate stabilization and ERK and p38 MAP kinase phosphorylation. Live cell fluorescence imaging thus enables characterization of signal transducers that are dynamically translocated following TCR engagement.