Cellular and molecular immunologic mechanisms in patients with atopic dermatitis

Atopic dermatitis is one of the most common chronic skin diseases among both adults and children.  Although it is often thought of as a skin disease, it also affects many organ systems. There remain a lot of gaps in our knowledge of atopic dermatitis, but researchers are developing a greater appreciation for its complexity of atopic dermatitis and introducing new treatments for this frustrating disease.

From an immunologic point of view, atopic dermatitis appears to be a collection of many different variants.  These endotypes are just recently beginning to be described, but involve the various arms of the immune system.  Defects in the innate immune system skew the skin towards inflammation; polarization of T-cells (Th2, Th17, and Th22) lead to further inflammation.  Other cell types, like dendritic cells, eosinophils, and mast cells, play important roles in the development of atopic dermatitis.  The interplay between immune cells and skin barrier proteins, like filaggrin, is also being explored.  Filaggrin influences cell differentiation, prevents water loss, and maintains the integrity of the skin barrier.  With defects in filaggrin, allergens penetrate deeper into the skin and bacteria like staphylococcus aureus are more likely to colonize the skin.

To make things even more complicated, as time progresses, so too does the disease, and patients can have an “atopic march” towards asthma, allergic rhinitis, and other allergic diseases.  Additionally, patients with atopic dermatitis have changes in the bacteria that colonize their skin and gut.  They have less microbial diversity, particularly when there is greater inflammation.  The role of these bacteria are being increasingly fleshed out with basic science and clinical research.

These insights are helping to guide new therapies.  In particular, dupilumab, an antagonist of the IL-4 receptor alpha chain, is showing promise in the treatment of atopic dermatitis.  And in those that don’t respond to dupilumab, there’s interest in other therapies like the IL-6 receptor antagonist tocilizumab.  As Werfel and colleagues note, it is difficult to find the best treatment for atopic dermatitis without knowing the pathophysiology behind the disease and its various endotypes (J Allergy Clin Immunol 2016; 138(2): 336-349).  In the future, with better knowledge, it may be possible to personalize appropriate treatment by identifying the correct endotype for each patient.

Multidisciplinary interventions in the management of atopic dermatitis

Atopic dermatitis is the most common skin disease in children, affecting up to 1 in 5 children in the United States.  But it doesn’t do it justice to call it just a skin disease.  The itching and scratching leads to a breakdown of the skin, disruptions in sleep, conflicts with parents, and an inability to concentrate at school.  Studies have shown that children with atopic dermatitis have a higher risk of developing mental health disorders like attention-deficit hypersensitivity disorder, anxiety, depression, conduct disorder, and autism.

Because atopic dermatitis does not have a single cause and has such far-ranging effects, management can be a challenge.  As LeBovidge and colleagues describe, multidisciplinary interventions are being investigated as a way to help these children (J Allergy Clin Immunol 2016; 138(2): 325-334).  Evaluation by an allergist or dermatologist can help to determine triggers, and education by nurses can help improve adherence and technique of applying emollients.  Psychologists can help redirect unhelpful compulsive behaviors like scratching into more helpful activities, such as re-application of moisturizers.  And nutritionists can ensure that children, especially those that have food allergies that require restriction of certain foods, receive enough Vitamin D and other nutrients.

Several institutions have embraced this multidisciplinary approach, but randomized controlled trials are limited.  Some group-based models have shown an improvement in control but others found no difference in disease severity, quality of life, or medical therapy use.  New models of collaboration between specialists and primary care providers are being developed in order to improve the quality of care.  It is hoped that improving the quality of care will decrease the economic burden of the disease.

Atopic dermatitis may be a skin disease, but its effects are felt in more than just the skin.  In order to get the disease under better control, new ways of delivering care will have to be developed.  Professionals in various fields, including allergists, dermatologists, nurses, nutritionists, and psychologists, are aligning with parents to break the itch-scratch cycle that causes such misery to the millions to have atopic dermatitis.

Multifactorial skin barrier deficiency and atopic dermatitis: Essential topics to prevent the atopic march

Some things are so evident that we take them for granted.  Take our skin for example.  We live in our skin and, for the most part, don’t give a second thought about it.  But skin is more than meets the eye.  It is vital for immunity, not only because it protects us from the outside but also because it fine tunes how our immune system responds to the various stimuli it encounters.  For those who have atopic dermatitis, a type of allergic disease that affects the skin leading it to become dry, irritated, and thickened, we see one result of a poor skin function.  In this month’s issue of JACI, Egawa and Kabashima discuss the role of skin barrier dysfunction in atopic dermatitis (J Allergy Clin Immunol 2016; 138(2): 350-358).

To understand the skin, we have to think about it in layers.  The topmost layer, called the stratum corneum, is a little like a wall, with flattened cells called corneocytes working like bricks and intercellular lipids functioning as mortar.  Together, they maintain the integrity of the skin.  But in atopic dermatitis, the wall is weakened.  Mutations in filaggrin, a protein important in making the corneocytes, have been associated with an increased risk of developing atopic dermatitis.

With the growing knowledge of genetics and immunology, there are beginning to be great insights into how atopic dermatitis starts to take hold.  In addition to filaggrin mutations, there’s a host of newer mutations that lead to the irritation, peeling, and thickening of the skin.  Mutations in genes encoding some proteins, like LEKTI and KLKs, have to do with the way that skin desquamates, or sheds, whereas others, like CLDN1, influence the tight junctions that maintain the integrity of the skin barrier.  And, in addition to these structural proteins, the immunologic messengers, particularly type 2 cytokines like IL-4, IL-13, IL-31, and IL-33, are found to be key in the development of atopic dermatitis.

As Egawa and Kabashima note, the skin is a very complex organ, and one that we are just starting to understand from an immunologic perspective.  Its importance cannot be overstated, not only because it brings us closer to figuring out what causes diseases like atopic dermatitis, but also because it opens the door towards finding new, effective medications and therapies that can target proteins like filaggrin.  In turn, this can improve the lives of the millions who live with atopic dermatitis, and the diseases that are associated with it.