Imaging flow cytometry (ImFC) represents a significant technological advancement in the field of cytometry, effectively merging the high-throughput capabilities of flow analysis with the image-based features of microscopy. In this comprehensive review article, we take a historical perspective and delve into the evolution of this methodology, presenting its past, exploring current state-of-the-art and forecasting potential future advancements. The inception of ImFC arose from the innovative combination of a flow cytometer's hydraulics with the technology of an advanced camera. This synergistic coupling facilitated the morphological analysis of cell populations at a high-throughput scale, effectively evolving the landscape of cytometry. However, the application of ImFC faced several challenges. Among the most prominent ones, is the development and implementation of software systems that can reliably and efficiently handle the robust data acquisition and analysis inherent in ImFC. The scale and complexity of the data generated by ImFC necessitates the creation of novel analytical tools that can effectively manage and interpret this data, thus allowing us to unlock the full potential of ImFC. Interestingly, artificial intelligence (AI) algorithms have begun to be implemented on ImFC, offering a promise for enhancing analytical capabilities. The adaptability and learning capacity of AI may prove to be essential in knowledge mining from high-dimensional data produced by ImFC, potentially enabling more accurate analyses. Looking forward, we project that ImFC may become an indispensable tool, not only in research laboratories but also in clinical settings. Given the unique combination of high-throughput cytometry and detailed imaging offered by ImFC, we foresee a critical role for this technology in the next generation of scientific research and diagnostics. As such, we encourage both current and future scientists to consider the integration of ImFC as an addition to their research toolkit and clinical diagnostic routine.

Background: Dysregulation of the immune response in the course of COVID-19 has been implicated in critical outcomes. Lymphopenia is evident in severe cases and has been associated with worse outcomes since the early phases of the pandemic. In addition, cytokine storm has been associated with excessive lung injury and concomitant respiratory failure. However, it has also been hypothesized that specific lymphocyte subpopulations (CD4 and CD8 T cells, B cells, and NK cells) may serve as prognostic markers for disease severity. The aim of this study was to investigate possible associations of lymphocyte subpopulations alterations with markers of disease severity and outcomes in patients hospitalized with COVID-19. Materials/Methods: A total of 42 adult hospitalized patients were included in this study, from June to July 2021. Flow-cytometry was used to calculate specific lymphocyte subpopulations on day 1 (admission) and on day 5 of hospitalization (CD45, CD3, CD3CD8, CD3CD4, CD3CD4CD8, CD19, CD16CD56, CD34RA, CD45RO). Markers of disease severity and outcomes included: burden of disease on CT (% of affected lung parenchyma injury), C-reactive protein and interleukin-6 levels. PO2/FiO2 ratio and differences in lymphocytes subsets between two timepoints were also calculated. Logistic and linear regressions were used for the analyses. All analyses were performed using Stata (version 13.1; Stata Corp, College Station, TX, USA). Results: Higher levels of CD16CD56 cells (Natural Killer cells) were associated with higher risk of lung injury (>50% of lung parenchyma). An increase in CD3CD4 and CD4RO cell count difference between day 5 and day 1 resulted in a decrease of CRP difference between these timepoints. On the other hand, CD45RARO difference was associated with an increase in the difference of CRP levels between the two timepoints. No other significant differences were found in the rest of the lymphocyte subpopulations. Conclusions: Despite a low patient number, this study showed that alterations in lymphocyte subpopulations are associated with COVID-19 severity markers. It was observed that an increase in lymphocytes (CD4 and transiently CD45RARO) resulted in lower CRP levels, perhaps leading to COVID-19 recovery and immune response homeostasis. However, these findings need further evaluation in larger scale trials.

Accurate quantification of immune cell subpopulations is essential for understanding immune responses in research and clinical settings. Flow cytometry (FC) is widely used for immune cell phenotyping, providing rapid and quantitative single-cell resolution. However, tissue-based pathological assessment offers additional spatial and morphological context that is often necessary for a comprehensive understanding of immune cell distribution. Traditionally, these methods are applied separately to different specimens, limiting direct comparative analysis. Here, we describe a simple combined approach to immune cell quantification that integrates both FC and pathology analysis within the same tissue specimen of colon biopsies. Tissue samples were divided into two portions: one processed into a single-cell suspension for FC-based characterization of CD45⁺, CD3⁺, CD4⁺, and CD8⁺ T cells and another formalin-fixed, paraffin-embedded (FFPE), and analyzed with hematoxylin and eosin (H&E) for eosinophils and immunohistochemistry (IHC) for CD4 and CD8. A pilot analysis of 10 samples shows high concordance of the results taken from the two methods, allowing for cross-validation between methodologies and improved diagnostic accuracy. This proof-of-principle study demonstrates the feasibility of an integrated workflow that combines FC and pathology for immune cell quantification, which provides assessment of immune cell populations from the limited material of intestinal biopsies with potential for improved diagnostic accuracy.

Aberrant signaling pathways of the acquired immune system are implicated in the development of cardiovascular disease (CVD) and chronic kidney disease (CKD) phenotypes. Understanding the complex abnormalities of lymphocyte subpopulations in CKD is a prerequisite for elucidating their implication in uremic cardiomyopathy. T cell subsets display various patterns of association with indices of myocardial function in both experimental and clinical CKD models. The role of Tregs in CVD and CKD has attracted significant research interest. Although experimental data suggest a protective role of Tregs from the development of arterial hypertension- and pressure overload-induced myocardial hypertrophy, there might be a change in the regulatory T cell (Treg) phenotype towards a profibrotic one in the settings of CKD and heart failure. Depletion of B lymphocytes is a hallmark of CKD and heart failure, bearing adverse prognostic significance, yet evidence of B lymphocytes’ involvement in the pathogenesis of myocardial damage is currently lacking. Considering that myocardial remodeling is the final outcome of diverse pathogenic processes targeting the heart, the aim of this review is to present the evidence available up to now regarding the role of acquired immune cells in the pathogenesis of the structural and functional alterations of the myocardium in CKD.