To describe recent findings on the effect of HIV/SIV infection on lymph node viral and T-cell dynamics using imaging-based methodologies.Chronic infection, particularly HIV/SIV, alters dramatically the microenvironment, immune cell frequency, distribution, function and tissue organization of secondary lymphoid tissues. These changes are not always reversible. Over the past few years, the implementation of advanced imaging protocols on human lymph node biopsies as well as on longitudinal lymphoid tissues samples from nonhuman primates (NHP) have provided a wealth of information on how local immune responses evolve over time in response to a persisting retroviral pathogen. Most of the information concerns cytotoxic and helper T cells and viral dynamics. In this review, we detail this information focusing on HIV/SIV infection. We also comment on the gaps that imaging technologies have bridged in our understanding and discuss the translational value of these new findings in the light of emerging therapeutic agendas.Novel imaging platforms allow for dissecting the spatiotemporal dynamics of immune interactions further improving our understanding of the interplay between virus and host and providing important information for designing successful preventive and curative strategies.
Abstract The orchestrated interaction between follicular helper CD4 T cells (TFH) and germinal center (GC) B cells is crucial for optimal humoral immunity. However, the regulatory mechanisms behind spatial distribution and function of TFH is not well understood. Here, we studied human TFH cells and found that transitioning to a CD57 hi TFH status was associated with distinct positioning in the GC, phenotype, transcriptional signatures, function and downregulation of their T-cell receptor (TCR). Single cell TCR clonotype analysis indicated a unidirectional transition towards the CD57 hi TFH status, which was marked with drastic changes in the nature of immunological synapse formation where peripheral microclusters become dominant. Lack of central supra molecular activation cluster (cSMAC) formation in TFH synapse was associated with enhanced ubiquitination/proteasome activity in these cells. Our data reveal significant aspects of the tissue organization and heterogeneity of follicular adaptive immunity and suggest that CD57 hi TFH cells are endowed with distinctive programming and spatial positioning for optimal GC B cell help. One Sentence Summary human TFH cell heterogeneity
In Listeria monocytogenes the acid tolerance response (ATR) takes place through a programmed molecular response which ensures cell survival under unfavorable conditions. Much evidence links ATR with virulence, but the molecular determinants involved in the reactivity to low pHs and the behavior of acid-exposed bacteria within host cells are still poorly understood. We have investigated the effect of acid adaptation on the fate of L. monocytogenes in human macrophages. Expression of genes encoding determinants for cell invasion and intracellular survival was tested for acid-exposed bacteria, and invasive behavior in the human myelomonocytic cell line THP-1 activated with gamma interferon was assessed. Functional approaches demonstrated that preexposure to an acidic pH enhances the survival of L. monocytogenes in activated human macrophages and that this effect is associated with an altered pattern of expression of genes involved in acid resistance and cell invasion. Significantly decreased transcription of the plcA gene, encoding a phospholipase C involved in vacuolar escape and cell-to-cell spread, was observed in acid-adapted bacteria. This effect was due to a reduction in the quantity of the bicistronic plcA-prfA transcript, concomitant with an increase in the level(s) of the monocistronic prfA mRNA(s). The transcriptional shift from distal to proximal prfA promoters resulted in equal levels of the prfA transcript (and, as a consequence, of the inlA, hly, and actA transcripts) under neutral and acidic conditions. In contrast, the sodC and gad genes, encoding a cytoplasmic superoxide dismutase and the glutamate-based acid resistance system, respectively, were positively regulated at a low pH. Morphological approaches confirmed the increased intracellular survival and growth of acid-adapted L. monocytogenes cells both in vacuoles and in the cytoplasm of interferon gamma-activated THP-1 macrophages. Our data indicate that preexposure to a low pH has a positive impact on subsequent challenge of L. monocytogenes with macrophagic cells.
