Natural killer (NK) cells are cytotoxic lymphocytes that play an important role in tumor immunosurveillance, preferentially eliminating targets with low or absent expression of MHC class I and stress-induced expression of ligands for activating NK receptors. Platelets promote metastasis by protecting disseminating tumor cells from NK cell immunosurveillance, but the underlying mechanisms are not well understood. In this study, we show that tumor cells rapidly get coated in the presence of platelets in vitro, and circulating tumor cells of cancer patients display coexpression of platelet markers. Flow cytometry, immunofluorescent staining, confocal microscopy, and analyses on an ultrastructural level using immunoelectron microscopy revealed that such coating may cause transfer of MHC class I onto the tumor cell surface resulting in high-level expression of platelet-derived normal MHC class I. The resulting "phenotype of false pretenses" disrupts recognition of tumor cell missing self, thereby impairing cytotoxicity and IFN-g production by NK cells. Thus, our data indicate that platelets, by conferring an unsuspicious "pseudonormal" phenotype, may enable a molecular mimicry that allows metastasizing tumor cells to downregulate MHC class I, to escape T-cell-mediated immunity without inducing susceptibility to NK cell reactivity. Cancer Res; 72(2); 440-8. Ó2011 AACR.

Defects in the DNA repair mechanism nucleotide excision repair (NER) may lead to tumors in xeroderma pigmentosum (XP) or to premature aging with loss of subcutaneous fat in Cockayne syndrome (CS). Mutations of mitochondrial (mt)DNA play a role in aging, but a link between the NER-associated CS proteins and base excision repair (BER)-associated proteins in mitochondrial aging remains enigmatic. We show functional increase of CSA and CSB inside mt and complex formation with mtDNA, mt human 8-oxoguanine glycosylase (mtOGG)-1, and mt single-stranded DNA binding protein (mtSSBP)-1 upon oxidative stress. MtDNA mutations are highly increased in cells from CS patients and in subcutaneous fat of aged Csbm/m and Csa−/− mice. Thus, the NER-proteins CSA and CSB localize to mt and directly interact with BER-associated human mitochondrial 8-oxoguanine glycosylase-1 to protect from aging- and stress-induced mtDNA mutations and apoptosis-mediated loss of subcutaneous fat, a hallmark of aging found in animal models, human progeroid syndromes like CS and in normal human aging.

Background: Interleukin (IL)-23 is involved in the pathogenesis of the chronic inflammatory Crohn disease. Pyoderma gangrenosum (PG) is often associated with and can even be the first manifestation of this disease and has abundant neutrophilic infiltration. Because IL-23 plays a critical role in driving inflammation associated with IL-17 production and especially neutrophil recruitment, we suspect that PG might be driven by a pathogenetic mechanism similar to that of inflammatory bowel diseases or psoriasis. Observations: Tissue sample analysis showed highly elevated expression of IL-23 on both transcriptional and protein level in a recalcitrant PG lesion. On the basis on these data, a treatment targeting the p40 subunit of the heterodimeric IL-23 with the monoclonal antibody ustekinumab was started. Therapy with ustekinumab resulted in a significant decrease of IL-23 expression in PG and healing after 14 weeks of treatment. No relapse occurred in a 6-month follow-up period. Conclusions: Our data provide evidence of an IL-23dominated inflammatory infiltrate in PG. This might specify a new concept for PG pathophysiology and suggests a possibility for using ustekinumab as a therapeutic agent in this disease.

A 13-year-old girl developed a non-pruritic pityriasis rosea-like rash, which did not respond to topical corticosteroids or UV therapy but persisted for 2 years. The lymphohistiocytic infiltrate in the upper dermis showed mononuclear cells immunoreactive with S100, CD68, factor XIIIa and CD1a. Electron microscopic evaluation of these cells demonstrated lamellated dense bodies but no Birbeck granules, lipid vacuoles or cholesterol crystals. Two diagnoses were made: a primarily clinical diagnosis of generalized eruptive histiocytosis and a more cell-biology-based diagnosis of an indeterminate cell histiocytosis. Three years later, the lesions are showing spontaneous resolution, with loss of erythema and flattening. Our patient's indeterminate cells fulfil Rowden's classical definition (dendritically shaped epidermal non-keratinocytes without identifying cytoplasmic features), as well as Zelger's newer definition (cells with features of both macrophages and dendritic cells). A Christmas tree pattern has not been previously described in indeterminate cell histiocytosis. Development of indeterminate cell histiocytosis in the lesions of a healing pityriasis rosea might explain the unusual distribution pattern. The development of a skin disorder at the site of an unrelated, already healed skin disease is known as an isotopic response. Key

Role of cholesterol sulfate in epidermal structure and function: lessons from X-linked ichthyosis. Biochim Biophys Acta 2014;1841: 353e61. Hand JL, Runke CK, Hodge JC. The phenotype spectrum of X-linked ichthyosis identified by chromosomal microarray. J Am Acad Dermatol 2015;72:617e27.