Summary Background Psoriasis vulgaris is an inflammatory skin disease mediated by Th1 and Th17 cytokines, yet the relative contribution of interferon (IFN)-γ, interleukin (IL)-17 and IL-22 on disease pathogenesis is still unknown. Objectives In this study, we sought to identify the cytokines produced by skin-resident T cells in normal skin, localize the receptors for these cytokines, and examine how these cytokines alter gene expression profiles of the cells bearing cognate receptors. Methods We used intracellular cytokine staining and flow cytometry to evaluate T cell cytokine production, and immunohistochemistry and double-label immunofluorescence to localize cytokine receptors in skin. Gene array analysis of cytokine-treated keratinocytes was performed using moderated paired t-test controlling for false discovery rate using the Benjamini–Hochberg procedure. Results We demonstrate that T-helper cells producing IL-17, IL-22 and/or IFN-γ, as well as the cells bearing cognate cytokine receptors, are present in normal human skin. Keratinocytes stimulated with IL-17 expressed chemokines that were different from those induced by IFN-γ, probably contributing to the influx of neutrophils, dendritic cells and memory T cells into the psoriatic lesion. In contrast, IL-22 downregulated genes associated with keratinocyte differentiation and caused epidermal alterations in an organotypic skin model. Conclusions Our results suggest that the Th17 cytokines IL-17 and IL-22 mediate distinct downstream pathways that contribute to the psoriatic phenotype: IL-17 is more proinflammatory, while IL-22 retards keratinocyte differentiation.

Psoriasis is a common, immune-mediated genetic disorder of the skin and is associated with arthritis in approximately 30% of cases. Previously, we localized PSORS2 (psoriasis susceptibility locus 2) to chromosomal region 17q25.3-qter after a genome-wide linkage scan in a family of European ancestry with multiple cases of psoriasis and psoriatic arthritis. Linkage to PSORS2 was also observed in a Taiwanese family with multiple psoriasis-affected members. In caspase recruitment domain family, member 14 (CARD14), we identified unique gain-of-function mutations that segregated with psoriasis by using genomic capture and DNA sequencing. The mutations c.349G>A (p.Gly117Ser) (in the family of European descent) and c.349+5G>A (in the Taiwanese family) altered splicing between CARD14 exons 3 and 4. A de novo CARD14 mutation, c.413A>C (p.Glu138Ala), was detected in a child with sporadic, early-onset, generalized pustular psoriasis. CARD14 activates nuclear factor kappa B (NF-kB), and compared with wild-type CARD14, the p.Gly117Ser and p.Glu138Ala substitutions were shown to lead to enhanced NF-kB activation and upregulation of a subset of psoriasis-associated genes in keratinocytes. These genes included chemokine (C-C motif) ligand 20 (CCL20) and interleukin 8 (IL8). CARD14 is localized mainly in the basal and suprabasal layers of healthy skin epidermis, whereas in lesional psoriatic skin, it is reduced in the basal layer and more diffusely upregulated in the suprabasal layers of the epidermis. We propose that, after a triggering event that can include epidermal injury, rare gain-of-function mutations in CARD14 initiate a process that includes inflammatory cell recruitment by keratinocytes. This perpetuates a vicious cycle of epidermal inflammation and regeneration, a cycle which is the hallmark of psoriasis.

Myeloid dermal dendritic cells (DCs) accumulate in chronically inflamed tissues such as psoriasis. The importance of these cells for psoriasis pathogenesis is suggested by comparative T cell and DC cell counts, where DCs outnumber T cells. We have previously identified CD11c+BDCA-1+ cells as the main resident dermal DC population found in normal skin. We now show that psoriatic lesional skin has two populations of dermal DCs: 1) CD11c+BDCA-1+ cells which are phenotypically similar to those contained in normal skin, and 2) CD11c+BDCA-1− cells which are phenotypically immature and produce inflammatory cytokines. While BDCA-1+ DCs are not increased in number in psoriatic lesional skin compared to normal skin, BDCA-1− DCs are increased 30-fold. For functional studies, we FACS-sorted psoriatic dermal single cell suspensions to isolate these two cutaneous DC populations, and cultured them as stimulators in an allo-MLR. Both BDCA-1+ and BDCA-1− myeloid dermal DC populations induced T cell proliferation, and polarized T cells to become Th1 and Th17 cells. In addition, psoriatic dermal DCs induced a population of activated T cells that simultaneously produced IL-17 and IFN-γ, which was not induced by normal skin dermal DCs. As psoriasis is believed to be a mixed Th17/Th1 disease, it is possible that induction of these IL-17+IFNγ+ cells is pathogenic. These cytokines, the T cells that produce them, and the inducing inflammatory DCs may all be important new therapeutic targets in psoriasis.

Macrophages are important cells of the innate immune system, and their study is essential to gain greater understanding of the inflammatory nature of psoriasis. We used immunohistochemistry and double-label immunofluorescence to characterize CD163+ macrophages in psoriasis. Dermal macrophages were increased in psoriasis compared to normal skin and were identified by CD163, RFD7, CD68, LAMP2, Stabilin-1, and MARCO. CD163+ macrophages expressed C-lectins CD206/MMR and CD209/DC-SIGN, as well as co-stimulatory molecules CD86 and CD40. They did not express mature DC markers CD208/DC-LAMP, CD205/DEC205 or CD83. Microarray analysis of in vitro derived macrophages treated with IFNγ showed that many of the genes upregulated in macrophages were found in psoriasis, including STAT1, CXCL9, Mx1 and HLA-DR. CD163+ macrophages produced inflammatory molecules IL-23p19 and IL-12/23p40 as well as TNF and iNOS. These data demonstrate that CD163 is a superior marker of macrophages, and identifies a subpopulation of “classically activated” macrophages in psoriasis. We conclude that macrophages are likely to be contributing to the pathogenic inflammation in psoriasis, a prototypical Th1 and Th17 disease, by releasing key inflammatory products.

Tumor-associated macrophages (TAMs) may have an important role in tumor immunity. We studied the activation state of TAMs in cutaneous SCC, the second most common human cancer. CD163 was identified as a more abundant, sensitive, and accurate marker of TAMs when compared with CD68. CD163(+) TAMs produced protumoral factors, matrix metalloproteinases 9 and 11 (MMP9 and MMP11), at the gene and protein levels. Gene set enrichment analysis (GSEA) was used to evaluate M1 and M2 macrophage gene sets in the SCC genes and to identify candidate genes in order to phenotypically characterize TAMs. There was coexpression of CD163 and alternatively activated "M2" markers, CD209 and CCL18 (chemokine (C-C motif) ligand 18). There was enrichment for classically activated "M1" genes in SCC, which was confirmed in situ by colocalization of CD163 and phosphorylated STAT1 (signal transducer and activator of transcription 1), IL-23p19, IL-12/IL-23p40, and CD127. Also, a subset of TAMs in SCC was bi-activated as CD163(+) cells expressed markers for both M1 and M2, shown by triple-label immunofluorescence. These data support heterogeneous activation states of TAMs in SCC, and suggest that a dynamic model of macrophage activation would be more useful to characterize TAMs.