A unique new type of T cells have apparently been “hiding in plain site,” say scientists invested in studying T cell involvement in rheumatoid arthritis, an autoimmune disorder.
Rheumatoid arthritis (RA) is the most common type of autoimmune arthritis, characterized by inflamed joints, low energy, appetite loss, and rheumatoid nodules, hard lumps that grow under the skin near the elbow and hands.
Like other autoimmune diseases, RA is a result of an immune response that goes awry; instead of recognizing human cells as harmless self cells, the immune system triggers an inflammatory response against them. However, other than understanding this general process, scientists are not completely sure what causes RA.
But now a new study provides some insight into the RA mystery, thanks to the discovery of a new type of T cell: “peripheral helper” T cells (Tph). These T cells are similar to follicular helper T cells (Tfh), but they have significant genetic and functional differences. For example, Tph cells are able to travel to RA-affected joint tissue where they interact locally with B cells. Tfh cells on the other hand, only induce B cell differentiation within the lymph nodes.
The new study, from scientists at the University of Birmingham, used mass cytometry to observe Tph cells after their migration to the synovial membrane in RA-affected joints and then global transcriptomics to differentiate Tph cells from Tfh cells. The synovial membrane consists of a layer of connective tissue that lines all joints and tendon sheaths.
The study researchers found that the journey Tph cells embark on into inflamed RA tissues is regulated by unique expression of chemokine receptors, chemical immune messengers employed for a variety of immune signaling duties. The researchers came to this conclusion after observing Tph cells inducing plasma differentiation in the lab.
“Our findings imply that Tph cells are uniquely poised to promote B-cell responses and antibody production within pathologically inflamed non-lymphoid tissues, and suggest a promising novel treatment target for autoimmune disease such as RA,” explained study co-author professor Christopher Buckley.
The current research surrounding Tph cells and RA has yet to demonstrate a clear cause and effect, but a connection between Tph cells and RA is undeniable. And perhaps, scientists think, maybe Tph cells are connected to other autoimmune diseases as well.
The recent study was published in the journal Nature.