IL-32 is expressed by human primary keratinocytes and modulates keratinocyte apoptosis in atopic dermatitis.
BACKGROUND
Keratinocyte (KC) apoptosis is an important mechanism of eczema and spongiosis in patients with atopic dermatitis (AD) and is mediated by IFN-gamma, which is secreted by T(H)1 cells. IL-32 is a proinflammatory cytokine that is involved in the inflammatory processes of rheumatoid arthritis, chronic obstructive pulmonary disease, and Crohn disease. Recently, it was shown that upregulation of IL-32 induces apoptosis.


OBJECTIVE
The aim of the study was to investigate the expression and function of IL-32 in patients with AD.


METHODS
The expression of IL-32 in KCs was analyzed by means of RT-PCR, ELISA, and flow cytometry. Transfections of small interfering RNA were performed in primary KCs, and apoptosis was analyzed by means of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling, annexin-V, and 7-amino actinomycin D stainings. Immunofluorescence stainings were used to detect IL-32 in skin biopsy specimens, and serum levels of IL-32 were analyzed by means of ELISA.


RESULTS
We report that IL-32 is expressed in human primary KCs on stimulation with IFN-gamma, TNF-alpha, and T(H)1 cells in contrast to T(H)2, regulatory T (Treg), or T(H)17 cells, which showed no effect. Transfection of primary KCs and artificial skin equivalents with small interfering RNA to IL-32, which resulted in a clear decrease in IL-32 expression, significantly reduced KC apoptosis. Immunofluorescence staining demonstrated that IL-32 was expressed in AD lesional skin, whereas it was present in neither skin biopsy specimens from healthy donors nor in lesional skin from patients with psoriasis. Serum levels of IL-32 from patients with AD correlated with disease severity, but increased serum levels of IL-32 were also detected in asthmatic patients.


CONCLUSIONS
The present study demonstrates KCs as a source of IL-32, which modulates KC apoptosis and contributes to the pathophysiology of AD.
Swiss Institute of Allergy and Asthma Research (SIAF), University of Zurich, Davos, Switzerland; High-altitude Clinic of Davos, Davos-Wolfgang, Switzerland.
Norbert
N
Meyer
Maya
M
Zimmermann
Simone
S
Bürgler
Claudio
C
Bassin
Stefan
S
Woehrl
Katharina
K
Moritz
Claudio
C
Rhyner
Philippe
P
Indermitte
Peter
P
Schmid-Grendelmeier
Mübeccel
M
Akdis
Günter
G
Menz
Cezmi A
CA
Akdis
D017209:Apoptosis / Q000187:drug effects*; D002478:Cells, Cultured; D003876:Dermatitis, Atopic / Q000276:immunology* / Q000503:physiopathology*; D006801:Humans; D007378:Interleukins / Q000378:metabolism* / Q000494:pharmacology; D015603:Keratinocytes / Q000276:immunology / Q000378:metabolism* / Q000502:physiology; D013601:T-Lymphocytes / Q000276:immunology
C496971:IL32 protein, human; D007378:Interleukins