Of mice and men–simultaneous detection of RNA and protein validates a mouse model to study human type 2 inflammation of the lung.

Dr. Elia Tait Wojno, Dr. David Artis, and colleagues at Cornell University have uncovered new immunological mechanisms involved in the regulation of type 2 inflammation of the lung that can be present in allergy and parasitic infection. Dr. Wojno demonstrated for the first time that expression of a specific prostaglandin receptor (PGD2-CRTH2) regulates the in vivo accumulation of lymphoid cells in the lung. These cells are involved in both infection and lymphoid disease.

Type 2 innate lymphoid cells (ILC2) are a rare type of immune cell that are important in the protective immune response. ILC2 cells have only recently been identified, and ILC cells, in general, lack the typical cellular lineage markers that are commonly used to phenotype other immune cell types. Isolation, detection, and analysis in the lung is especially challenging because ILC2 cells are enriched in non-lymphoid tissues, and many ILC-specific tools and reagents to analyze them are not yet available.

The Cornell team took a multi-faceted approach to building greater understanding of the influence of PGD2-CRTH2 on ICL2 behavior, and its possible role in pulmonary inflammation. Initially, they sought to determine if there were tissue-specific differences in the presence of the receptor in human ILC2 cells. Using multi-color flow cytometry, they discovered a population of cells that had the characteristics of ILC2 cells, with differential presence of the receptor in lung versus blood. They then wanted to determine if these differences were also conserved in mice, so that they could use mice as an experimental model. While there is an antibody available against the human receptor, there is no such antibody for mice, so they could not use classical antibody-based detection methods. To circumvent this challenge, the team used PrimeFlow® RNA Assays to look simultaneously at the presence of ILC-class receptor protein and the expression of the CRTH2 gene. Expression results from PrimeFlow RNA Assays were validated with RT-PCR. These experiments revealed that the distribution of ILC2 in mice was consistent with that in humans, allowing the team to continue its studies in mice. Finally, the team used ELISA and intracellular staining with eBioscience antibodies to confirm that purified mouse ILC2 cells do produce cytokines in response to prostaglandin.

"PrimeFlow RNA Assay has great power to look at things that you wouldn't be able to see otherwise."

To compare these results to the behavior of ILC2 in vivo, the team turned to infection by Nippostrongylus brasiliensis, a parasitic worm of rodents with a life cycle similar to human hookworm. As the parasite migrates to the lungs, chronic type 2 pulmonary inflammation with emphysyma-like pathology may develop. Their experiments revealed that this inflammation in mice has all the hallmarks of type 2 immune response in humans. Dr. Wojno's studies demonstrate how simultaneous detection of proteins and RNA can be used to analyze rare cell types without the need to perform laborious cell sorts, and may contribute to our understanding of the mechanisms of type 2 inflammation of the lung in allergy and other pulmonary disorders.
