Biology subjects

Graw, F.

Publications and source records attributed to Graw, F..

4 recordsLinked to original sources

bioRxiv2022

Inferring cell motility in complex environments with incomplete tracking data

Cell motility has important influence on cell interactions and functionality for various biological aspects. Deciphering these dynamics often relies on live-cell microscopy measurements, which partly have to deal with limitations that could impair a reliable quantification of their motility. Especially given complex environments and tissue structures, limited observation periods, cells moving in and out of focus and impaired calibration of observation axes often lead to loss of cell tracks and insufficient tracking of motility within several dimensions. However, a reliable quantification of cell motility dynamics is essential when aiming at extrapolating the observed dynamics in order to understand cell population dynamics at larger temporal and spatial scales using appropriate simulation environments. To analyze how incomplete observations affect interpretation and parameterization of cell motility, we combined experimental observations with computational models. Studying individual cell dynamics within 3D collagen environments, we found that the gradual loss of cell tracks leads to an underestimation of several motility parameters with the effect dependent on the collagen density. By extending the automated fitting strategy FitMultiCell to account for cell track loss, we show that we are able to retrieve the actual cell dynamics and, thus, to reliably parameterize cell motility from such incomplete data. Applying our approach to the analysis of CD4+ T cells within 3D collagen environments that were infected with HIV-1, we could show that despite a considerable loss of cell tracks, the data still contained sufficient information to compare individual cell motilities by inferring and simulating their dynamics. Thereby, the analysis allowed us to disentangle the effect of HIV-1 infection and collagen density on individual cell motility. Our extended FitMultiCell-approach presented here provides a solution for the elimination of artifacts from cell track data analysis to robustly infer cell motility dynamics.

systems biology↗

bioRxiv2021

Constant rate of Plasmodium falciparum sexual commitment promotes variable gametocyte proportions as infection progresses over time

Plasmodium falciparum infections persist through long dry seasons at low parasitaemia without causing malaria symptoms and thus remain untreated. In asymptomatic children, increased circulation of infected erythrocytes without adhering to the vascular endothelium is observed during the dry months, compared to febrile malaria in the wet season. However, alterations of parasite sexual commitment and gametocytogenesis have not been investigated. Here, we compared the expression of genes related to sexual commitment and gametocytogenesis, the proportion and density of P. falciparum gametocytes, and the blood concentration of phospholipids in dry season asymptomatic individuals versus symptomatic subjects in the wet season. Additionally, we adapted a within-host mathematical model considering asexual and sexually-committed parasites and gametocytes to understand the dynamics of gametocyte number and proportion as infections progress. Compared to clinical malaria cases, transcripts of late-stage gametocytes were predominantly upregulated in the dry season, associating with increased proportions of mature gametocytes; while transcription of genes related to parasite sexual commitment was unaltered throughout the year. Our data suggest that gametocyte density and proportion diverge as infections progress from recent transmission to chronic carriage, without alterations in the sexual commitment rate over time.

microbiology↗

bioRxiv2021

HCV spread kinetics reveal varying contributions of transmission modes to infection dynamics

Hepatitis C virus (HCV) is capable of spreading within a host by two different transmission modes: cell-free and cell-to-cell. Although viral dissemination and diffusion of viral particles facilitates the infection of distant cells, direct cell-to-cell transmission to uninfected neighboring cells is thought to shield the virus from immune recognition. However, the contribution of each of these transmission mechanisms to HCV spread is unknown. To dissect the contribution of these different transmission modes to HCV spread, we measured HCV lifecycle kinetics and used an in vitro spread assay to monitor HCV spread kinetics after low multiplicity of infection in the absence and presence of a neutralizing antibody that blocks cell-free spread. By analyzing these data with a spatially-explicit mathematical model that describes viral spread on a single-cell level, we quantified the contribution of cell-free and cell-to-cell spread to the overall infection dynamics and show that both transmission modes act synergistically to enhance the spread of infection. Thus, the simultaneous occurrence of both transmission modes likely represents an advantage for HCV that may contribute to the efficient establishment of chronic infection. Notably, the relative contribution of each viral transmission mode appeared to vary dependent on different experimental conditions and suggests that viral spread is optimized according to the environment. Together, our analyses provide insight into the transmission dynamics of HCV and reveal how different transmission modes impact each other. ImportanceHepatitis C Virus can spread within a host by diffusing viral particles or direct cell-to-cell transfer of viral material between infected and uninfected cells. To which extend these cell-free and cell-to-cell transmission modes contribute to HCV spread, establishment of chronicity and antiviral escape is still unknown. By combining in vitro experimental HCV spread data with a multi-scale mathematical model we have disentangled the contribution and interplay of cell-free and cell-to-cell transmission modes during HCV infection. Our analysis revealed synergistic effects between the two transmission modes, with the relative contribution of each transmission mode varying dependent on the experimental conditions. This highlights the adaptability of the virus and suggests that transmission modes might be optimized dependent on the environment, which could contribute to viral persistence.

microbiology↗

bioRxiv2021

Locally confined IFNγ production by CD4+ T cells provides niches for murine cytomegalovirus replication in the salivary gland

Cytomegalovirus (CMV) has evolved a unique virus-host relationship in the salivary glands (SGs) to sustain prolonged viral replication and hence chances for horizontal transmission. Previous reports have established a decisive role for IFN{gamma} producing CD4+ T cells to control murine CMV (MCMV) infection in the SGs; however, micro-anatomical information regarding their mode of action is largely missing. Here, we provide a spatiotemporal analysis of defined antiviral immune actions that eventually culminate in control of lytic MCMV replication in this preferred mucosal niche. CXCR3-mediated guidance of CD4+ T cells towards CXCL9 and CXCL10 expressing cells resulted in discrete clusters close to infection foci where they reported TCR engagement and produced IFN{gamma}. Of note, these clusters occasionally contained CD11c+ antigen-presenting cells with engulfed virus-associated remnants, most likely apoptotic bodies derived from previously infected cells, enabling antigen presentation to CD4+ T cells. The induced IFN{gamma} production within these CD4+ T cell accumulations triggered IFN{gamma}R signaling in a confined perimeter, thereby inducing local, but not organ-wide protection, and allowing MCMV replication to continue at not yet protected sites. Combining experimental data with a mathematical model of the spatiotemporal dynamics of infection and CD4+ T cell dynamics revealed a scenario, in which ultimate MCMV control is achieved through accumulating sites of regionally-confined tissue protection.

immunology↗