Brian J. Nickoloff

Skin immune sentinels in health and disease

Human skin and its immune cells provide essential protection of the human body from injury and infection. Recent studies reinforce the importance of keratinocytes as sensors of danger through alert systems such as the inflammasome. In addition, newly identified CD103+ dendritic cells are strategically positioned for cross-presentation of skin-tropic pathogens and accumulating data highlight a key role of tissue-resident rather than circulating T cells in skin homeostasis and pathology. This Review focuses on recent progress in dissecting the functional role of skin immune cells in skin disease.

Stat3 links activated keratinocytes and immunocytes required for development of psoriasis in a novel transgenic mouse model

Here we report that epidermal keratinocytes in psoriatic lesions are characterized by activated Stat3. Transgenic mice with keratinocytes expressing a constitutively active Stat3 (K5.Stat3C mice) develop a skin phenotype either spontaneously, or in response to wounding, that closely resembles psoriasis. Keratinocytes from K5.Stat3C mice show upregulation of several molecules linked to the pathogenesis of psoriasis. In addition, the development of psoriatic lesions in K5.Stat3C mice requires cooperation between Stat3 activation in keratinocytes and activated T cells. Finally, abrogation of Stat3 function by a decoy oligonucleotide inhibits the onset and reverses established psoriatic lesions in K5.Stat3C mice. Thus, targeting Stat3 may be potentially therapeutic in the treatment of psoriasis.

Characterization of intercellular adhesion molecule-1 and HLA-DR expression in normal inflamed skin: Modulation by recombinant gamma interferon and tumor necrosis factor

Lymphocytes bind to cultured keratinocytes that are treated with interferon gamma (IFN-gamma) and tumor necrosis factor (TNF). When the lymphocytes are preincubated with antibody to lymphocyte function associated antigen-1 (LFA-1), this adherence is inhibited. Because intercellular adhesion molecule-1 (ICAM-1) is a ligand for LFA-1, we studied the cellular expression of ICAM-1, as well as two other IFN-gamma-inducible antigens, (HLA) human lymphocyte antigens DR and DQ, in both normal and diseased skin. The modulation of these cell surface antigens by IFN-gamma and TNF with the use of short-term organ cultures of skin was compared with isolated keratinocytes grown in a conventional tissue culture system. While in normal skin, keratinocytes did not express HLA-DR, DQ, or ICAM-1, when organ cultures were supplemented with IFN-gamma, rapid induction of keratinocyte ICAM-1 expression occurred after 24 hours; HLA-DR but not DQ expression occurred after 48 hours. TNF also induced keratinocyte ICAM-1 expression (although to a lesser degree than IFN-gamma) but did not induce either keratinocyte HLA-DR or DQ expression. There was good correlation of keratinocyte expression of ICAM-1 and HLA-DR by IFN-gamma and TNF when the epidermis of the organ culture system was compared with the isolated keratinocytes grown in tissue culture. The presence of intraepidermal lymphocytes correlated extremely well with keratinocyte ICAM-1 expression but not with keratinocyte HLA-DR expression in psoriasis, atopic dermatitis, lichen planus, and mycosis fungoides. The intensity of endothelial cell expression of ICAM-1 correlated with the degree of dermal inflammation. We conclude that IFN-gamma, once produced by activated T lymphocytes in the dermis, may be of importance in lymphocyte trafficking in the epidermis by the induction of keratinocyte ICAM-1 expression. The use of the short-term organ culture system, in which there is inducible ICAM-1 expression, provides an experimental bridge between purely in vitro and in vivo investigations to further our understanding of the molecular basis for lymphocyte apposition to keratinocytes in the skin.

Recent insights into the immunopathogenesis of psoriasis provide new therapeutic opportunities

Chronic and excessive inflammation in skin and joints causes significant morbidity in psoriasis patients. As a prevalent T lymphocyte-mediated disorder, psoriasis, as well as the side effects associated with its treatment, affects patients globally. In this review, recent progress is discussed in the areas of genetics, the immunological synapse, the untangling of the cytokine web and signaling pathways, xenotransplantation models, and the growing use of selectively targeted therapies. Since psoriasis is currently incurable, new management strategies are proposed to replace previous serendipitous approaches. Such strategic transition from serendipity to the use of novel selective agents aimed at defined targets in psoriatic lesions is moving rapidly from research benches to the bedsides of patients with this chronic and debilitating disease.

Dermal injection of immunocytes induces psoriasis.

Establishing direct and causal relationships among the confederacy of activated cell types present in psoriasis has been hampered by lack of an animal model. Within psoriatic plaques there are hyperplastic keratinocytes, infiltrating immunocytes, and activated endothelial cells. The purpose of this study was to determine if psoriasis is primarily a disorder of keratinocytes or the immune system. Using a newly developed experimental system in which full-thickness human skin is orthotopically transferred onto severe combined immunodeficient mice, autologous immunocytes were injected into dermis, and the resultant phenotype characterized by clinical, histologic, and immunophenotypic analyses. Engraftment of samples included both uninvolved/ symptomless (PN) skin removed from patients with psoriasis elsewhere, or from healthy individuals with no skin disease (NN skin). In 10 different experiments involving 6 different psoriasis patients, every PN skin was converted to a full-fledged psoriatic plaque skin by injection of autologous blood-derived immunocytes. In all but one psoriatic patient, the immunocytes required preactivation with IL-2 and superantigens to convert PN skin into psoriatic plaque skin. In every case, resultant plaques were characterized by visible presence of flaking and thickened skin, loss of the granular cell layer, prominent elongation of rete pegs with a dermal angiogenic tissue reaction, and infiltration within the epidermis by T cells. Lesional skin displayed 20 different antigenic determinants of the psoriatic phenotype. None of the four NN skin samples injected with autologous immunocytes converted to psoriatic plaques. We conclude that psoriasis is caused primarily by the ability of pathogenetic blood-derived immunocytes to induce secondary activation and disordered growth of endogenous cutaneous cells including keratinocytes and vascular endothelium.

Perturbation of epidermal barrier function correlates with initiation of cytokine cascade in human skin

BACKGROUND An important function of skin is to serve as a barrier and thus provide protection from the external environment. The epidermal keratinocyte establishes this barrier by producing an intact stratum corneum. In the past, keratinocytes were appreciated only for this rather inert, passive structural responsibility and not for their potential dynamic contribution to inflammatory or immune-mediated reactions. OBJECTIVE Our purpose was to examine the cascade of molecular and cellular events that occur when the barrier function of human skin is abrogated by repeated tape stripping, which physically removes the stratum corneum without inducing any cytopathic effects on the underlying epidermal keratinocytes. METHODS Eight healthy human volunteers underwent repeated tape stripping and sequential punch biopsy specimens of skin obtained between 1 and 24 hours after tape stripping were analyzed for protein antigens by immunostaining of cryostat-cut sections. The presence or absence of various messenger RNAs (mRNAs) were detected by polymerase chain reaction. RESULTS After repeated tape stripping, keratinocytes became activated within hours. The responses included up-regulation of keratin-16 expression and keratinocyte proliferation accompanied by production of a specific profile of cytokine and adhesion molecule mRNAs and proteins in both epidermal and dermal compartments. Polymerase chain reaction amplification of RNA species isolated from the epidermal portion of skin revealed increases 6 hours after tape stripping in mRNA coding for tumor necrosis factor-alpha, IL-8, IL-10, interferon gamma, intercellular adhesion molecule-1, transforming growth factor-alpha, and transforming growth factor-beta. There was no increase in tumor necrosis factor-alpha, IL-8, IL-10, or transforming growth factor-alpha mRNAs in the dermal samples. Immunostaining revealed that keratinocyte intercellular adhesion molecule-1 was increased 6 hours after stripping and was accompanied by endothelial cell expression of E-selectin (endothelial cell adhesion molecule-1) and vascular cell adhesion molecule-1. These molecular events, which occurred after 6 hours in tape-stripped skin, preceded any movement of inflammatory cells from the circulation into dermis or epidermis and hence reflect changes that occur in cells indigenous to normal human skin. None of these changes occurred in persons who underwent limited tape strippings without barrier perturbation. CONCLUSION The results highlight the rapid and distinctive responses of epidermal keratinocytes and demonstrate that these cells can actively participate in a far greater number of homeostatic responses other than the production of the epidermal barrier.

Spontaneous Development of Psoriasis in a New Animal Model Shows an Essential Role for Resident T Cells and Tumor Necrosis Factor-α

Psoriasis is a common T cell–mediated autoimmune disorder where primary onset of skin lesions is followed by chronic relapses. Progress in defining the mechanism for initiation of pathological events has been hampered by the lack of a relevant experimental model in which psoriasis develops spontaneously. We present a new animal model in which skin lesions spontaneously developed when symptomless prepsoriatic human skin was engrafted onto AGR129 mice, deficient in type I and type II interferon receptors and for the recombination activating gene 2. Upon engraftment, resident human T cells in prepsoriatic skin underwent local proliferation. T cell proliferation was crucial for development of a psoriatic phenotype because blocking of T cells led to inhibition of psoriasis development. Tumor necrosis factor-α was a key regulator of local T cell proliferation and subsequent disease development. Our observations highlight the importance of resident T cells in the context of lesional tumor necrosis factor-α production during development of a psoriatic lesion. These findings underline the importance of resident immune cells in psoriasis and will have implications for new therapeutic strategies for psoriasis and other T cell–mediated diseases.

Embryonic and tumorigenic pathways converge via Nodal signaling: role in melanoma aggressiveness

Bidirectional cellular communication is integral to both cancer progression and embryological development. In addition, aggressive tumor cells are phenotypically plastic, sharing many properties with embryonic cells. Owing to the similarities between these two types of cells, the developing zebrafish can be used as a biosensor for tumor-derived signals. Using this system, we show that aggressive melanoma cells secrete Nodal (a potent embryonic morphogen) and consequently can induce ectopic formation of the embryonic axis. We further show that Nodal is present in human metastatic tumors, but not in normal skin, and thus may be involved in melanoma pathogenesis. Inhibition of Nodal signaling reduces melanoma cell invasiveness, colony formation and tumorigenicity. Nodal inhibition also promotes the reversion of melanoma cells toward a melanocytic phenotype. These data suggest that Nodal signaling has a key role in melanoma cell plasticity and tumorigenicity, thereby providing a previously unknown molecular target for regulating tumor progression.

Cd-34 Is Expressed by a Distinctive Cell Population in Peripheral Nerve, Nerve Sheath Tumors, and Related Lesions

The pattern of CD-34 antigen (human progenitor cell antigen) immunoreactivity was studied within normal nerve, and a variety of nerve sheath and neuroectodermal tumors. Besides normal nerves, 111 soft tissue tumors were studied, including 17 neurofibromas, 10 neurilemomas, 12 malignant peripheral nerve sheath tumors, 1 melanocytic schwannoma, 21 fibroblastic lesions, 31 fibrohistiocytic lesions, seven neuroectodermal lesions, and 10 miscellaneous tumors. CD-34positive dendritic cells were consistently identified within the endoneurium of normal nerve, all neurofibromas, dermatofibrosarcomas, and Antoni B (but not Antoni A) areas of neurilemomas. CD-34 was not expressed in the majority (eight of 10 cases) of malignant peripheral nerve sheath tumors. CD-34 was also lacking in all fibroblastic lesions (nodular fasciitis, fibromatosis, keloid, fibrosarcoma) and in neuroectodermal tumors that are not generally considered to show true nerve sheath differentiation (neurotropic melanoma, clear cell sarcoma, neuroepithelioma). We conclude that CD-34 (or a closely related epitope) defines a normally occurring nerve sheath cell that appears to be cytologically and immunophenotypically distinct from a fibroblast and conventional Schwann cell. The antigen can also be localized to benign nerve sheath tumors, but tends to be lost in malignant ones. The consistent presence of CD-34 within all 13 cases of dermatofibrosarcoma protuberans can be used as evidence in support of the view that these lesions are variants of nerve sheath tumors, and distinct from benign fibrous histiocytomas which consistently lack the antigen. Finally, expression of CD-34 by one of three giant cell fibroblastomas reinforces the close relationship between this tumor and dermatofibrosarcoma protuberans.

Kaposiform hemangioendothelioma of infancy and childhood. An aggressive neoplasm associated with Kasabach-Merritt syndrome and lymphangiomatosis

We report the clinical and pathological features of nine distinctive, but relatively unknown, vascular tumors of infancy and childhood presenting as soft tissue masses often associated with locally aggressive disease, lymphangiomatosis and Kasabach-Merritt syndrome. The patients, four males and five females, were all in their first decade of life except for two (median, 2 years; range, 5 months to 19 years). These tumors involved deep soft tissues of the upper extremity (four cases), retroperitoneum (two cases), chest wall, scalp, and neck (one case each). Four patients also had Kasabach-Merritt syndrome, and three patients had lymphangiomatosis. Lymphangiomatosis consisted of diffusely infiltrating lymphangioma of soft tissue (three cases) and in two by the additional presence of bone lesions. In one of these three cases, lymphangiomatosis antedated the diagnosis of the vascular tumor, and in the remainder they were concurrently diagnosed. Tumors were characterized by infiltrating, interconnecting sheets or irregular nodules of slender endothelial cells lining crescentic or slit-like vessels and, less commonly, rounded capillary-type vessels. Within some tumors, nests of epithelioid endothelial cells with prominent eosinophilic cytoplasm containing finely granular hemosiderin, hyaline droplets, and cytoplasmic vacuoles were identified. Smaller amounts of hemosiderin were observed within the spindled endothelial cells and microthrombi could be seen occasionally within the tiny lumina. Nuclear atypia was minimal within these tumors and mitotic figures were infrequent, averaging 2 to 3/10 high-power fields (HPF) (range 0-7/10 HPF). Larger, well-formed feeding vessels were present at the periphery of the tumor. The endothelium of these vessels expressed factor VIII-AG, CD34, and bound Ulex europaeus, and muscle- specific actin. In contrast, the spindled tumor cells expressed only CD34. Human papilloma virus (HPV)-16- like DNA transcripts, which have been identified in cases of Kaposis sarcoma, were not detected by polymerase chain reaction in two cases. Follow-up information revealed that four patients were alive without disease after wide excision, multiple excision(s), or amputation (one case); three were alive with disease; and two died, one from lymphangiomatosis with respiratory compromise and the other from hemorrhage complicating Kasabach-Merritt syndrome. It appears that treatment should consist of wide local excision and supportive therapy for associated symptoms.