Intravital imaging in immunology: experimental and computational approaches

Thursday, June 17 at 02:15am (PDT)
Thursday, June 17 at 10:15am (BST)
Thursday, June 17 06:15pm (KST)

SMB2021 SMB2021 Follow Wednesday (Thursday) during the "MS17" time block.
Note: this minisymposia has multiple sessions. The second session is MS18-IMMU (click here).

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Barun Majumder (University of Tennessee, USA), Soumen Bera (University of Tennessee, USA)


Intravital Imaging with multi-photon microscopy is one of the most powerful tools to answer some of the longstanding fundamental questions of cell biology, tumor biology and immunology. New and emerging technologies in the field of intravital imaging have helped scientists study cell dynamics and interactions at very high resolutions in tissues in vivo. Based on the labeling and detection of a particular wavelength (fluorescence), the technique can provide insights on cell’s cardinal attributes like division, localization, migration and interaction in a molecular level in three dimensions over time. There are three major steps in the intravital imaging studies: the experimental design, data extraction and processing prior to use in analysis, and the data analysis and mathematical modeling. In this proposed mini-symposium we will invite experts in the area of experimental immunology and mathematical modeling to discuss the challenges, advancements, limitations and accomplishments made in the field in the context of immunology and cell biology.

Joost Beltman

(Division of Drug Discovery and Safety, Leiden Academic Centre for Drug Research, Leiden University, The Netherlands, The Netherlands)
"Quantifying the role of T cells in tumor control through computational modeling"
Immunotherapies are an emerging strategy for treatment of solid tumors, for example by means of adoptive T cell therapies and stimulation of T cell functionality by specific antibodies. Improved understanding of the mechanisms employed by cytotoxic T lymphocytes (CTL) to control tumors will aid in the development of immunotherapies. CTLs can directly kill tumor cells in a contact- dependent manner or may exert indirect effects on tumor cells via secretion of cytokines. Here, we aim to quantify the importance of these mechanisms in various settings by application of computational models to experimental data acquired in mice. We developed ordinary differential equation models and agent- based models (ABMs) of tumor regression following adoptive transfer of a population of CTLs. Models were parameterized based on in vivo measurements of CTL infiltration over time, tumor volume measurements, and on image-based quantification of rates of tumor cell proliferation and apoptosis. We find that in two different settings direct, contact-dependent killing was insufficient to cause tumor regression and that antiproliferative effects by T-cell-produced cytokines have a large role in tumor control. Thus, our work highlights the potential importance of cytokine-induced antiproliferative effects in T-cell–mediated tumor control.

Sachie Kanatani

(Johns Hopkins Bloomberg School of Public Health, USA)
"Comparative intravital imaging of human and rodent malaria sporozoites"
Malaria infection starts with the injection of Plasmodium sporozoites into the host's skin. Sporozoites are motile and move in the skin to find and enter blood vessels to be carried to the liver. We present the first characterization of P. falciparum sporozoites in vivo, analyzing their motility in mouse skin and human skin xenografts and comparing their motility to two rodent malaria species. These data suggest that in contrast to the liver and blood stages, the skin is not a species-specific barrier for Plasmodium. Indeed, P. falciparum sporozoites enter blood vessels in mouse skin at similar rates to the rodent malaria parasites. Furthermore, we demonstrate that antibodies targeting sporozoites significantly impact the motility of P. falciparum sporozoites in mouse skin. Though the sporozoite stage is a validated vaccine target, vaccine trials have been hampered by the lack of good animal models for human malaria parasites. Pre-clinical screening of next-generation vaccines would be significantly aided by the in vivo platform we describe here, expediting down-selection of candidates prior to human vaccine trials.

Irina Grigorova

(University of Michigan Medical School, USA)
"Studying the role of CCL3 in the interactions between Germinal Center B cells and follicular regulatory T cells"
Follicular regulatory T cells (Tfrs) play multiple roles in the control of B cells response. From one side, they repress autoreactive and foreign antigen-specific germinal center (GC) B cells at the peak of GC response. From the other side, they promote GC B cell cycling in IL-10 dependent fashion and ensure optimal affinity maturation. However, which factors direct GC B cell interactions with Tfr cells has been unclear. Based on the single cell and bulk qPCR analysis we found that CCL3 is upregulated in about 10% of CCs that express Myc and are undergoing positive selection. Both ex vivo chemotaxis analysis and multiphoton intravital imaging suggests that CCL3 produced by GC centrocytes (CCs) promotes their direct contacts with Tfr cells. qPCR and transwell analysis revealed expression and synergistic involvement of CCR5 and CCR1 chemokine receptors on Tfr cells in their chemotaxis to CCL3. Both an adoptive transfer and mixed bone marrow chimeras models suggest that at the peak of GC response CCL3 promotes moderate repression of GC response. However, after the peak of GC response B cell-intrinsic production of CCL3 promotes prolonged participation of B cells in GCs, affinity maturation, as well as better memory and plasmablast response. To summarize, our studies suggest the existence of the local chemotactic cues between B cells and Tfr cells within GCs that direct interactions between the cells and are important for optimal regulation of GC response.

Barun Majumder

(Department of Microbiology, University of Tennessee Knoxville, USA)
"Correlation between speed and turning naturally arises for sparsely sampled cell movements"
Mechanisms regulating cell movement are not fully understood. One feature of cell movement that determines how far cells displace from an initial position is persistence, the ability to perform movements in a direction similar to the previous movement direction. Persistence is thus determined by turning angles between two sequential displacements. Recent studies found that a cell's average speed and turning are negatively correlated, suggesting a fundamental cell- intrinsic program whereby cells with a lower turning ability (i.e., larger persistence) are intrinsically faster. Using simulations, we show that a negative correlation between the measured average cell speed and turning angle naturally arises for cells undergoing a correlated random walk due to sub- sampling, i.e., when the frequency of sampling is lower than frequency at which cells make movements. Assuming heterogeneity in persistence and intrinsic speeds of individual cells results in a negative correlation between average speed and turning angle that resembles experimentally observed correlations. Changing the frequency of imaging or calculating displacement of cohorts of cells with different speeds resulted in similar results whether or not there is a cell- intrinsic correlation between cell speed and persistence, and we could find many different parameter sets that allow to approximately match experimental data binned into cell cohorts. Interestingly, re-analysis of data of T cells in zebrafish showed that the observed correlation between persistence and speed is highly sensitive to sampling frequency, disappearing for coarsely sampled data. Our results thus challenge an established paradigm that persistent cells have intrinsically faster speeds and emphasize the role of sampling frequency may have on inference of critical cellular mechanisms of cell motility.

Hosted by SMB2021 Follow
Virtual conference of the Society for Mathematical Biology, 2021.