In Situ Characterization of Tissue-Resident Immune Cells by MALDI Mass Spectrometry Imaging

Abstract

Tissue-resident immune cells differ from their corresponding blood cells in many functional aspects. Although the proteome of blood immune cells has been well-investigated, there are almost no data on tissue-resident immune cells. Here, we explored the potential of using MALDI-TOF-MS imaging (MSI) to investigate these cells in colon tissue, which exhibits a strong infiltration of immune cells. MSI identified several proteinaceous markers that colocalized with specific structures of the colon, such as mucosa or muscularis mucosae, in six patients. In addition, we showed that certain m/z values have the same spatial distribution as CD3 T lymphocytes in the lymphoid follicular structures or as CD206 macrophages in the lamina propria. For further corroboration, blood lymphocytes and monocytes from 10 healthy volunteers were analyzed by intact cell mass spectrometry (ICMS). Furthermore, we analyzed monocyte-derived macrophages that had been polarized in vitro into proinflammatory M and anti-inflammatory M phenotypes. The mass spectra differed clearly among all immune cell types. Additionally, it was found that distinct signals from ICMS analysis were identical to the m/z values found in the MSI experiment in lymphoid follicular structures. These data show for the first time that MSI is well-suited to visualize the spatial distribution of immune cells in human colon tissue. We consider MALDI mass spectrometry imaging to be a technique with high potential for use in rapid investigations of tissue-specific features of cells.

Translating In Vitro T Cell Metabolic Findings to In Vivo Tumor Models of Nutrient Competition

“…These are well validated, and compatible with commonly used methods to identify immune cell localization and activity (Bennewith and Durand, 2004; He et al, 2008; Sukumar et al, 2013). Improvements in the resolution of mass spectrometry imaging techniques have also identified tissue-resident immune populations and metabolite gradients in tumors (Dilillo et al, 2017; Holzlechner et al, 2017). Additionally, sensitive reporter constructs could be useful to map the duration and regional location of nutrient limiting milieus.…”

Targeted Proteomics Comes to the Benchside and the Bedside: Is it Ready for Us?

“…With the growing field of immunotherapeutics in cancer biology, the study of immune cell infiltrations in solid tumors has gained attention. There is an interest in the localization information of different nonmalignant cell types to decipher the components of the specialized niche provided to the malignant cells . MRM assays can be designed for various cell markers that can unravel the composition of the microenvironment with the information regarding their localization.…”

Multimodal imaging of undecalcified tissue sections by MALDI MS and μXRF

“…Directly before MALDI MSI measurements were made, a dithranol matrix used for all the described MALDI imaging experiments was deposited by sublimation at 140°C with a home-built apparatus 40 yielding ∼0.2 mg matrix per cm 2 per slide. The choice of the matrix was made in accordance with the literature 41 and a protocol developed in-house.…”