Macrophages form dendrite-like pseudopods to enhance bacterial ingestion.

Abstract

Macrophages are critical innate immune cells that exhibit remarkable adaptability during pathogen infections. However, the relationship between their morphological plasticity and physiological functions remains largely elusive. Here, we discovered an unprecedented paradigm of macrophage adaptation within a few hours upon severe Gram-negative bacterial infections, characterized by the formation of dendrite-like pseudopods (DLPs). Using in vitro, microfluidic, and in vivo infection models, we demonstrate that these pseudopods enhance bacterial uptake by expanding the macrophage searching radius, thereby bolstering host defense. Mechanistically, Toll-like receptor 4 (TLR4) activation by Gram-negative bacterial lipopolysaccharide (LPS) upregulates the expression of macrophage-specific RhoGEF and ARHGEF3 in an NF-κB-dependent manner. ARHGEF3 localizes to dendrite-like pseudopods and enhances RhoA activity. Consequently, periodic cycles of actin assembly and disassembly propel the elongation of pseudopods, whereas vimentin intermediate filaments stabilize them. Importantly, infusion of DLP-equipped macrophages into Salmonella-infected mice reduced bacterial burden and infection severity. Together, our findings underscore how the dynamic response of macrophages to massive infections can augment immune defense against pathogenic bacteria.