Dea, C. | bioRxiv Science

bioRxiv2026

Macrophages discriminate and sort pathogenic bacteria and apoptotic material during dual-target phagocytosis

Macrophages are central to immune homeostasis, clearing both pathogens and apoptotic cells. While these processes share some features, they differ functionally: efferocytosis of apoptotic cells is typically anti-inflammatory, whereas bacterial uptake triggers strong inflammatory responses. During infections, both targets may coexist, yet how macrophages handle such complex particles is poorly understood. Previously, we showed that Pseudomonas aeruginosa adheres to apoptotic cells, forming stable composites that can be jointly phagocytosed. Here, using quantitative confocal and live-cell imaging, we investigate how macrophages engage and internalize these dual targets. We find that macrophages employ distinct strategies depending on target composition. Apoptotic cells alone are engulfed intact within tight, actin-rich membrane cups, whereas bacteria-laden apoptotic cells induce protrusive, actin-driven extensions that navigate along the apoptotic scaffold to access bacteria. Individual bacteria are selectively extracted and internalized, while apoptotic material is internalized in a piecemeal manner. Early phagosome analysis shows that most contain either bacteria or apoptotic material alone, with mixed cargo being less frequent. These findings demonstrate that macrophages can discriminate and sort the components of complex targets during uptake, revealing a previously unrecognized sophistication in phagocytic processing. This work provides a framework for understanding how innate immune cells integrate pathogen clearance while managing apoptotic material.

cell biology↗

bioRxiv2022

Reversible adhesion by type IV pili leads to formation of irreversible localized clusters

Despite the fact a fundamental first step in the physiopathology of many disease-causing bacteria is the formation of long-lived, localized, multicellular clusters, the spatio-temporal dynamics of the cluster formation process, particularly on host tissues, remains poorly understood. Experiments on abiotic surfaces suggest that the colonization of a surface by swimming bacteria requires i) irreversible adhesion to the surface, ii) cell proliferation, and iii) a phenotypic transition from an initial planktonic state. Here, we investigate how Pseudomonas aeruginosa (PA) infects a polarized MDCK epithelium and show that contrary to what has been reported on the colonization of abiotic surfaces, PA forms irreversible bacterial clusters on apoptotic epithelial cell without requiring irreversible adhesion, cell proliferation, or a phenotypic transition. By combining experiments and a mathematical model, we reveal that the cluster formation process is regulated by type IV pili (T4P). Furthermore, we unveil how T4P quantitatively operate during adhesion on the biotic surface, finding that it is a stochastic process that involves an activation time, requires the retraction of pili, and results in reversible adhesion with a characteristic attachment time. Using a simple kinetic model, we explain how such reversible adhesion process leads to the formation of irreversible bacterial clusters and quantify the cluster growth dynamics.

biophysics↗