Applying high-resolution mass spectrometry imaging to visualize parasite-host interaction

Abstract text

Introduction

Parasite-host interaction is on a mutual relationship: Parasites depend on nutrients from their host, and the host organism fights against exploiting its resources, leading to inflammation. Both effects affect the lipid composition and distribution.

High-resolution atmospheric-pressure scanning microprobe matrix-assisted laser desorption/ionization mass spectrometry imaging (AP-SMALDI MSI) is a powerful tool to localize and identify lipids in biological samples.

Objectives

We aimed to visualize the impact of parasitic infection on the lipid profile of host tissue. We studied two different parasite-host models: Besnoitia besnoiti, forming cysts in bovine skin, and Schistosoma mansoni eggs, inducing granuloma formation in livers of hamsters as infection models.

Materials & Methods

AP-SMALDI MSI was performed on an AP-SMALDI5-AF ion source (TransMIT GmbH, Giessen, Germany) coupled to a high-resolution orbital trapping mass spectrometer (Q Exactive, Thermo Fisher Scientific, Bremen, Germany), enabling high lateral resolution (≥5 um pixel size) to depict fine structures in the tissue and high mass accuracy (resolution R=240000 at m/z 200) to analyze hundreds of biomolecules in parallel.

Cryosections (20 µm thick) of tissue samples were prepared using a cryomicrotome (HM 525, Thermo Fisher Scientific) and coated with matrix using a pneumatic sprayer (SMALDIprep, TransMIT GmbH) before analysis.

Data were uploaded to the Metaspace platform, and analytes were annotated using LipidMaps. Statistical analyses led to a list of up- and down-regulated compounds. MS images of these ions were created, enabling manual assignment to specific, parasite-induced structures (e.g., cysts, granuloma).

Results

We found lipids characteristic for infection in parasite-host systems.

For S. mansoni, specific lipids were found to be up- or downregulated in granuloma regions around the eggs. We even visualized very small features, such as Schistosoma eggs, inside the granuloma. Additionally, substructures within the granulomas were identified based on lipids with characteristic distributions.

For B. besnoitia, specific lipids for cyst walls and cyst content were identified, resulting in mass spectrometric images resembling H&E stained sections.

Conclusion

Using MSI, we analyzed parasites inside their host. This opens the door for future studies of different parasite-host systems, comparison of parasitic life stages, and analyzing drug-treated infected samples.