Bacterial infection of macrophages induces decrease in refractive index

Area of Science:

• Cell biology
• Microscopy
• Infectious diseases

Background:

• Pathogen infection causes host cell structural and biochemical changes.
• Label-free imaging is crucial for studying these dynamic cellular modifications.

Purpose of the Study:

• To investigate structural modifications in host cells during Salmonella infection using digital holographic microscopy (DHM).
• To determine if refractive index changes in infected cells are pathogen-induced and related to inflammation or cell death.

Main Methods:

• Utilized digital holographic microscopy (DHM) for label-free imaging.
• Measured the integral refractive index (RI) distribution of primary murine bone marrow-derived macrophages (BMDM).
• Compared RI in BMDM infected with Salmonella enterica serovar Typhimurium versus uninfected cells, including caspase-1 deficient cells.

Main Results:

• Salmonella-infected BMDM exhibited a significant reduction in refractive index (RI) compared to uninfected cells.
• Infected BMDM from caspase-1 deficient mice also showed a similar decrease in RI.
• These findings indicate the RI reduction is pathogen-induced and not dependent on caspase-1-mediated inflammation or cell death.

Conclusions:

• The observed decrease in refractive index of Salmonella-infected BMDM is a direct result of the pathogen.
• Digital holographic microscopy (DHM) shows potential for real-time monitoring of host-pathogen interactions.
• This label-free technique offers a novel approach to study cellular responses to infection.