Analyzing subsets of immune cells in the salivary gland by examining the cells’ epigenetic makeup is a viable way to measure inflammation that may aid in diagnosing and monitoring people with Sjögren’s syndrome, a study suggests.
These data were reported in the journal Rheumatology in the paper, “Epigenetically quantified immune cells in salivary glands of Sjögren’s syndrome patients: a novel tool that detects robust correlations of T follicular helper cells with immunopathology.”
Sjögren’s syndrome is usually diagnosed by taking a biopsy of the salivary gland and looking for abnormally high numbers of immune cells. This approach has a number of drawbacks: it can be subjective, there is little standardization for how to process samples, and looking for “immune cells” under a microscope doesn’t really give much information — there are many types of immune cells that, while wildly different in terms of function, can’t be distinguished from each other just by looking at them.
Additional molecular tests better able to specifically determine the characteristics of immune cells in salivary glands in Sjögren’s syndrome are needed. In this study, researchers tested one such method, called epigenetic cell counting (ECC).
Every cell in the body has all the same genetic information (with rare exceptions). But an individual cell really needs only a fraction of that information to do its particular function. Thus, cells “turn off” some genes via methylation — the addition of a methyl group to the DNA, which is a well-documented type of epigenetic alteration (changes in gene expression, or whether a cell “reads” a gene as active or inactive).
The idea behind ECC is that, because different types of cells will “turn off” different genes, cell types can be determined by measuring which genes are or aren’t methylated.
In theory, this isn’t really different from how cell types have traditionally been distinguished – by measuring this phenomenon at the level of what RNA or proteins a cell makes. But epigenetic cell counting has a few advantages. Most notably, DNA is more stable than other biological molecules, so samples can be stored for longer periods of time before they are analyzed without the risk of getting unreliable results.
The researchers used ECC on salivary biopsy samples from 57 patients with sicca (dry mouth): 29 people with primary Sjögren’s syndrome, five with secondary Sjögren’s syndrome (caused by another autoimmune disease), 10 with incomplete Sjögren’s syndrome (evidence of autoimmune activity, but not meeting the diagnostic criteria), and 13 without Sjögren’s syndrome (dry mouth, but no evidence of this being due to autoimmune disease).
This method was indeed able to identify different types and subsets of immune cells in these samples. Non-Sjögren’s syndrome samples had fewer immune cells, such as B- and T-cells, than did samples from people with primary or secondary Sjögren’s syndrome. Those with incomplete Sjögren’s syndrome tended to have higher levels of some cell types, but not others.
With the aid of computer algorithms, the researchers divided the patients into groups based on this cellular information. This division identified a subset of people who had particularly high evidence of immune cell infiltration and B-cell activation, suggestive of more severe disease. In particular, patients with high numbers of a type of immune cell called a T follicular helper cell tended to have worse disease.
Although the very small sample size used makes it difficult to draw broad conclusions, the data do act as a proof-of-concept for this method in Sjögren’s syndrome. Further studies with more people will be needed to validate these results and determine what marker(s) measured by ECC are most useful.
The researchers concluded that ECC could be used, on its own or in combination with other methods, to “aid in diagnostics, prognostics and monitoring of therapy responses in clinical trials in the future.”