When I talked to Jon Hanifin last year he mentioned an intriguing fact: eczema comes in two general types. About 80% of atopic eczema patients have allergies and high levels of IgE antibodies. But twenty per cent of patients have eczema without allergies.
The technical term for allergic eczema is “extrinsic” atopic dermatitis; the non-allergic kind is “intrinsic” AD.
Production of IgE—and most antibodies—is activated by type 2 helper T cells. So scientists have generally assumed that extrinsic AD patients had overactive type 2 helper T cells. But new research shows that type 2 helper T cells are overactive in both intrinsic and extrinsic AD patients.
The scientists, led by Emma Guttman-Yassky at Rockefeller University in New York City, analyzed skin and blood samples from 42 extrinsic and 9 intrinsic AD patients, looking at molecular and cellular differences in the immune system and the skin.
They found that type 2 helper T cell activation is actually higher in intrinsic AD patients than extrinsic AD patients. In fact, markers of inflammation in general are higher in intrinsic AD.
|Figure 6 from the paper. Scientists now resort to “word clouds” to convey the complexity of molecular biology!|
The results are surprising. Patients with intrinsic AD generally do not go on to develop asthma or allergic rhinitis; yet if you just looked at their helper T cells you’d think they were guaranteed to experience even more severe allergies than those suffered by extrinsic AD patients.
So what’s keeping down the IgE levels in intrinsic AD? In the paper, the authors speculate freely, but so far there is no answer.
It also appears that a special class of helper T cells known as type 17 (so-called because they produce the signaling molecule IL-17A) are also more active in intrinsic than extrinsic AD. It’s not clear yet how scientists might use this knowledge to design therapies more specific than current T cell-suppressing options such as ciclosporin, which can have severe side effects.
The research suggests that future T-cell related therapies will likely be similar for intrinsic and extrinsic AD, despite the different nature of the disease in the two patient groups.
Hat tip to KMO.