Dynamics of phagocytosis through interplay of forces

TL;DR

This study models the interactions between bacteria and phagocytes as forces influencing their dynamics, revealing regimes of bacterial decline or growth and transitions characterized by bi-stability, providing new insights into phagocytosis processes.

Contribution

It introduces a minimalist force-based framework to analyze the collective dynamics of bacteria and phagocytes, highlighting the interplay of attraction and repulsion forces.

Findings

Attraction-dominated regimes lead to bacterial decline.

Repulsion-dominated regimes cause bacterial clustering and phagocyte trapping.

A transition regime exhibits bi-stability between the two behaviors.

Abstract

Phagocytosis is the process by which cells, which are 5 to 10 times larger than the particle size, engulf particles, holding substantial importance in various biological contexts ranging from the nutrient uptake of unicellular organisms to immune system of humans, animals etc. While the previous studies focused primarily on the mechanism of phagocytosis, in this study we have a taken a different route by studying the dynamics of the phagocytes in a system consisting of many bacteria and a small number of phagocytes. We put forward a minimalist framework that models bacteria and phagocytes as active and passive circular disks, respectively. The interactions are governed by directional forces: phagocytes are attracted toward bacteria, while bacteria experience a repulsive force in proximity to phagocytes. Bacteria are capable of reproduction at a fixed rate, and the balance between bacterial reproduction and phagocytic engulfment is governed by the interplay of the two opposing forces. In attraction dominated regimes, bacterial populations decrease rapidly, while in repulsion dominated regimes, bacterial clusters grow and impede phagocytes, often resulting in phagocyte trapping. Conversely, in attraction-dominated scenarios, only a few bacteria remain at later times, rendering the motion of the phagocytes diffusive. Further, the transition between the two regimes occurs through a regime of bi-stability. Our study further describes the dynamics of both species using the tools of statistical analysis, offering insights into the internal dynamics of this system.