This natural killer cell interacts with the CD94/NKG2A receptor, part of a system believed to have been in place in humans for more than 90 million years.
“We believe there is a possible role for the innate immune system in the development of psoriatic arthritis and its distinction from psoriasis,”, declared at the annual meeting of the American College of Rheumatology.
Dr. Chandran, of the University of Toronto, presented anof a discovery cohort comprising 1,155 patients with dermatologist-diagnosed psoriasis of greater than 10 years duration, 664 rheumatologist-diagnosed psoriatic arthritis patients, and 3,118 controls, all participants in the International Psoriasis and Arthritis Research Team program. These findings were then independently confirmed in a separate University of Toronto replication cohort of 659 psoriasis patients, 1,177 psoriatic arthritis patients of European ancestry, and 1,096 controls.
By way of background, the rheumatologist explained that psoriasis and psoriatic arthritis are known to differ in terms of their genetic architecture, the biggest difference being in the HLA class I region, where HLA-C predominates in psoriasis and HLA-B in psoriatic arthritis. These structurally unrelated forms of HLA class I are known to educate natural killer cells and shape their function. Dr. Chandran and his coinvestigators were eager to shed new light on the mechanisms by which this leads to rheumatic disease.
Humans can be divided into three groups based upon whether they are HLA-B21 methionine/methionine (M/M), HLA-B21 M/threonine (T), or HLA-B21 T/T. The B21 M types educate CD94/NKG2A-positive natural killer cells by delivering functional peptides to the CD94/NKG2A receptor, while the B21 T/T version does not.
In the discovery cohort, individuals with psoriatic arthritis turned out to be 36% more likely to be HLA-B21 M/M or HLA-B21 M/T than were the psoriasis patients, while the psoriasis patients were 22% less likely to be B21 M–positive than controls. These relationships were confirmed in the replication cohort, where psoriatic arthritis patients were 40% more likely to be B21 M–positive than psoriasis patients, and psoriasis patients were 18% less likely to be B21 M–positive than controls, with all of these differences being statistically significant.
While this is translational science, Dr. Chandran explained that it has important clinical implications. He and his coinvestigators are developing a genetic marker panel to differentiate psoriatic arthritis from psoriasis, as are other research groups. And the Toronto investigators are now convinced that including HLA-B21 M/M and HLA-B21 M/T in their evolving genetic test is worthwhile in terms of boosting the test’s predictive power. The 36%-40% increased risk of psoriatic arthritis associated with B21 M–positivity isn’t sufficiently large for it to serve as a standalone test, but when the genetic test panel is finalized and the investigators can evaluate its positive and negative predictive value, it will be clear that the B21 M component will provide added value, he predicted.
Because psoriatic arthritis can take on a variety of disparate forms clinically, Dr. Chandran and his coworkers believe their genetic test will prove most useful for nonrheumatologists, especially dermatologists and primary care physicians.
He reported having no relevant financial relationships regarding this study, funded by the Canadian Institutes of Health Research, the Krembil Foundation, and the Arthritis Foundation.
SOURCE: Chandran V et al. Arthritis Rheumatol. 2018;70(Suppl 10),