IL-23p19 has an inside job in endothelial cells

IL-12 cytokine family is full of surprises. Ordinarily, these cytokines (IL-12, IL-23, IL-27, IL-35) are made of two heterodimeric sub-units. But one after another, each of the sub-units were found to have an independent function.  

Latest in these series is a study from Science Signaling that showed that human endothelial cells express intra-cellular IL-23p19 that signals via gp130 molecules mimicking IL-6.

Initially, the authors showed that endothelial cells from Giant-cell arteritis (GCA) patients express IL-23p19 subunit, but not another IL-23p40 subunit (while I support fully-human studies, in controversial situations such as this, I preferred if the authors have included confirmation staining on IL-23p19 KO cell from KO mice or CRISPR/Cas9 edited IL-23p19 KO human cells). 

Next, in vitro experiments with primary human umbilical vein endothelial cells (HUVECs) and human dermal microvascular endothelial cells (HDMECs) confirmed selective expression of IL-23p19 within endothelial cells in response to pro-inflammatory signaling.

IL-23p19 was detected in endothelial cell lysate but not in supernatants, suggesting that it was intra-cellular protein and wasn't secreted in culture medium.

Mechanistically, IL-23p19 transduced endothelial cells up-regulated adhesion molecules (VCAM-1, ICAM-1, PECAM-1) and induced gp130-dependent STAT3 activation.

The authors hypothesized that IL-23p19 could be similar to viral IL-6 (vIL-6), a viral cytokine product of human herpesvirus 8 (HHV-8, also known as Kaposi’s sarcoma-associated herpesvirus).

In summary, this study provided evidence that in humans IL-23p19 could have an independent biological function in endothelial cells by promoting adhesion and recruitment of inflammatory cells thus contributed to vasculitis.

David Usharauli

α-IL23, not α-IL17 antibody blockade, shows protection in IBD model

Previous studies indicated that cytokines IL-23 and IL-17 act in concert to induce and perpetuate autoimmune inflammation. This is certainly true for psoriatic skin inflammation.

However, two new back-to-back studies in journal Immunity provided evidence that when it comes to intestine inflammation, role of IL-23 and IL-17 goes in opposite direction. Here, blockade of IL-17 exacerbate while blockade of IL-23 inhibits intestine pathology and gut wall permeability.

Both studies came from research groups working in biotech/biopharma (Daniel Cua's group at Merck Research Laboratories and Jennifer Towne's group at Amgen [presently at Janssen]). Both studies reached similar conclusions. 

Here, the authors treated colitis-prone mice with blocking antibodies specific for IL-23 or IL-17 cytokine family. Surprisingly, both α-IL17A or α-IL17RA treatment worsened gut pathology, while α-IL23 (p40 or p19 subunits) antibody showed protection.

Unlike α-IL23, α-IL17RA antibody treatment was associated with increased gut wall permeability (serum sCD14 and LBP), implying IL-17 role in gut health.

Similar increased gut leakage (with FITC-dextran) was observed by Merck's team in chemical irritant DSS-induced GI inflammation model in IL-17KO mice (though Amgen's team did not observe it in DSS mouse model with α-IL17 treatment. It could be that α-IL17 antibody blockade did not fully inhibit IL-17 action as it could be expected in IL-17KO mice).

Additional experiments showed that γδ T cells were the main producers of gut IL-17 in DSS model and that γδ T cell KO mice showed the same increased GI tract permeability as IL-17KO mice.

Finally, Merck's team showed that (a) γδ T cell-derived IL-17 production in the gut were mostly IL-23 independent and (b) IL-23rKO mice were protected against worsening GI wall pathology.

In overall, these two studies suggest that local gut tissue associated IL-23 independent but γδ T cell-derived IL-17 production plays a protective role in gut permeability. Basically, this means that α-IL23 blockade, but not α-IL17 pathway inhibition, would most likely provide benefits to patients suffering from GI tract idiopathic inflammation.

David Usharauli

Pain sensing neurons alert dendritic cells for presence of skin fungal parasites

IL-23/IL-17 axis plays important role in the host's defense against fungal parasites. Recent studies show that skin CD11b⁺ dendritic cells and skin γδ T cells contribute for anti-fungal protection.

New study in journal Immunity added yet another layer of protection to the skin. It showed that skin pain and thermal sensing TRPV1 neurons also sensing the presence of fungal parasite and alert local immune defense system.

Using mouse model of candida albicans fungal infection, the authors first re-confirmed that cytokine IL-17 showed anti-fungal activity.

Next, the authors showed that the source of this protective IL-17 were skin γδ T cells (and not conventional αβ T cells or non-conventional dendritic epidermal T cells (DETCs).

Next, the authors re-confirmed that IL-23 was upstream of IL-17 in host's protection against candida albicans fungal infection.

Next, the authors showed that skin langerhans cells (LCs) and Batf3 ⁺ CD103⁺ DCs (LC^Δ Batf3 ^Δ) were dispensable for anti-fungal protection.

However, the authors found that IL-23 derived from C-type lectin positive dermal DCs (using Mgl2-DTR + IL-23KO BM chimera) were necessary for this protection.

Afterwards, the authors found that ablation of skin nociceptors, TRPV1, decreased anti-fungal protection.

Finally, the authors found that upon detection of candida albicans, CGRP (calcitonin gene related peptide) secreted by TRPV1 neurons acted on Mgl2+ dermal DCs to induce IL-23 secretion that in turn induce protective IL-17 from local skin γδ T cells (strangely, however, Fig. 6H and 6I do not match the authors text in the results. Here, -DT+CGRPα samples should have significantly lower CFU compared to +DT+CGRPα samples, since DT depletes Mgl2+ DCs).

In summary, these results provide additional support for neuro-immune network affecting host's protection against infection. This does not mean that neurons are important for ultimate clearance of the pathogen. Here, the authors only showed day 3 of infection when there is a maximum burden of fungal pathogen.

However, there is also a broader implications. Mainly, how CNS can influence or even imitate local immune response and produce or augment skin inflammation such as in psoriasis, dermatitis, eczema, urticaria and skin allergies.  

David Usharauli

Antibody targeting IL-23(p19 subunit) beats psoriasis

Psoriasis is a common skin inflammation of autoimmune nature. If there is any disease that benefited from the fundamental immunological research is Psoriasis.

Initially thought to be a purely skin disorder, now it is firmly established that immune system's attack on it own skin tissue plays a major role in driving clinical signs of psoriasis. Pioneering studies with α-p40 antibodies suggested that IL-12 might have been involved in psoriasis. However discovery of IL-23 (that consisted of p40 and p19 subunits) in 2001 opened up new era in our understanding of molecular mechanisms behind psoriasis pathology.

New study in Nature provided additional data to clearly establish that selective targeting of IL-23 drastically improves psoriasis's skin pathology.

The authors showed that three, monthly intravenous injections of humanized antibody targeting p19 subunit of IL-23 (Tildrakizumab) could drastically reduce psoriatic skin pathologies in absolute majority of patients that lasted for at least 1 year.

α-p19 antibody injections reduced hyper-keratinization and hyper-proliferation in psoratic skin lesions.

In summary, this study suggests that IL-23 system that includes IL-17 are intimately involved in psoriatic skin pathology and its targeting (maybe simultaneously with α-IL-17 ) could finally bring the needed relief to people suffering from this skin disorder.

 David Usharauli

Stress-release with IL-22

Type II Diabetes (T2D) is part of a complex metabolic syndrome. Typically, conditional insulin deficiency as observed during T2D is a result of an imbalance between production and demand for insulin. I always wondered why would nature develop such a system where packaging of excess glucose would be controlled by a single molecule (insulin), while glucose unpacking, it's release into bloodstream are controlled by so many molecules, including corticosteroids.

Prevalence of T2D is increasing in modern population. Speculation varies as to the cause of such increase in T2D (availability of excess food, poor physical activity, widespread use of broad-spectrum antibiotics causing changes in gut microflora, etc).

Frequently the metabolic syndrome is associated with the changes in immune cytokines. Occasionally, immune cytokines are directly implicated in disease, for example IL-17 and TNF-alpha in psoriasis or rheumatoid arthritis.

On other hand, the list of immune cytokines are constantly expanding and maybe some of them would show a beneficial effect.

This new paper in Nature Medicine is one such research. This study, led by Michael McGuckin from the University of Queensland (Australia), has uncovered the protective role for cytokine IL-22 in T2D. 

IL-22 is a member of IL-10 cytokine super-family that includes IL-10, IL-22, IL-24, IL-26, so far.

Using in vitro assay to measure beta cell ER stress, the authors showed that IL-23, IL-24, IL-33 were the potent inducers of ER stress.

Parallel experiments with beta cell exposure to the pairwise combination of cytokines revealed that IL-22 (and IL-10) could reverse ER stress caused by any other cytokines examined, including IL-23, IL-24, IL-33. Two exceptions were IL-17A for IL-22 and IL-17F for IL-10 for which the effectiveness of such inhibition were less prominent.

As a consequence of reduced ER stress, IL-22 was able to improve secretion of insulin from primary mouse beta islets.

Importantly, using high-fat diet induced obesity mouse model (HF-DIO mouse), the authors showed that in vivo treatment with IL-22 could reduce beta cell ER stress and reverse decline in insulin secretion in response to HF diet.

In addition, IL-22 treatment could reverse high-fat diet effect on body weight and glucose tolerance.  

Mechanistically, this beneficial effect of IL-22 was associated with decrease in ER-stressor inflammatory cytokines and in increase for enzymes responsible for neutralization of free radicals.

Finally, the authors showed that this beneficial effect of IL-22 could be reproduced in an in vitro experiments with human beta islets as well.

In summary, this figure-packed research showed that IL-22 can have a protective characteristics beneficial for management of beta cell functions.

It is not immediately clear why immune cytokines play such important roles in non-immune functions. For example, why would IL-23 induce beta cell stress and reduce insulin secretion? Similarly, it is not clear why IL-22 would develop protective function for beta cells. Previous studies showed that IL-22 has a protective role in gut epithelial cell function (probably through it's effects on cell surface fucosylation). On the other hand, IL-22 has been implicated in promoting skin epithelial hyper-proliferation characteristic to psoriasis. So, the field is quite confusing, to say the least.

David Usharauli