Plasmacytoid Dendritic Cells in Cutaneous Disorders

Molluscum Contagiosum Virus: Biology and Immune Response

Molluscum contagiosum virus is a poxvirus belonging to the Poxviridae family, which includes Orthopoxvirus, Parapoxvirus, Yantapoxvirus, Molluscipoxvirus, Smallpox virus, Cowpox virus and Monkeypox virus. MCV belongs to the genus Molluscipoxvirus and has a tropism for skin tissue. MCV infects keratinocytes and, after an incubation period of 2 weeks to 6 weeks, causes a breakdown of the skin barrier with the development of papules of variable size depending on the proper functioning of the immune response (both adaptive and acquired). MCV only infects humans and does not cause viraemia. MCV encodes for several inhibitory proteins responsible to circumvent the immune response through different signalling pathways. Individuals who can be infected with MCV are children, immunocompromised individuals such as organ transplant recipients and Human Immunodeficiency Virus (HIV)-infected individuals. Current treatments to manage MCV-induced lesions are different and include the use of immunomodulators, which, however, do not provide an effective response.

Skin immune cell characterization in juvenile and adult Göttingen Minipigs

The skin hosts a sophisticated immune system involving responses from both innate and adaptive immune cell populations. Swine skin is close to human skin by its structure, composition and function. In addition, the minipig is considered the model of choice in toxicology studies for drugs applied by the dermal route and developed for both the adult and paediatric indications. However, knowledge on the skin immune system in minipigs, particularly in Göttingen Minipigs, is still limited. The objective of our work was first to characterize the main skin immune populations (Langerhans cells, dermal dendritic cells, macrophages and T lymphocytes) in Göttingen Minipigs. In parallel, we compared the skin immune populations from healthy and immunocompromised piglets following oral treatment with cyclosporin A (CsA) at 10 mg/kg/day. We also explored other pathological conditions using a contact dermatitis model in minipigs challenged with a sensitizer, 2,4-dinitrochlorobenzene (DNCB). Langerhans cells and dermal MHCII^lowCD163⁺ cells were increased one month after oral treatment with CsA at 10 mg/kg/day. The contact dermatitis model in Göttingen Minipigs challenged by DNCB suggested migration of Langerhans cells and dermal dendritic cells as well as T cell recruitment into the skin. These data bring new information in skin immunotoxicology in Göttingen Minipigs and could contribute to a better understanding of the effects of new therapeutic drugs on the developing immune system.

Distinguishing pustular psoriasis and acute generalized exanthematous pustulosis on the basis of plasmacytoid dendritic cells and MxA protein

BACKGROUND

Distinguishing acute generalized exanthematous pustulosis (AGEP) and pustular psoriasis (PS) can be challenging. Staining for plasmacytoid dendritic cells, or PDCs (producer of IFN-α/β), and MxA (an IFN-α/β inducible protein) may help discriminate these entities.

METHODS

Forty-three cases of AGEP and PS were compiled from two academic institutions. All cases were examined for CD123+ PDCs, eosinophils, acanthosis, papillomatosis, suprapapillary plate thinning, tortuous dilated capillaries, single necrotic keratinocytes, papillary dermal edema, vasculitis, eosinophil exocytosis, intraepidermal pustules, and subcorneal pustules. A subset of cases (n = 26) was stained for MxA.

RESULTS

Perivascular and intraepidermal PDCs, dilated tortuous vessels, and MxA expression in the dermal inflammatory infiltrate were significantly (P < 0.05) in favor of a diagnosis of PS. The absence of PDCs and presence of eosinophils favored a diagnosis of AGEP (P < 0.05).

CONCLUSIONS

We found compelling evidence for the use of CD123 to highlight PDCs in these cases. The presence of PDCs and expression of MxA in dermal inflammatory infiltrate, as well as absence of eosinophils and presence of tortuous dilated capillaries favored a diagnosis of PS. Expression of MxA in the dermal infiltrate corresponds with a Th1 pathway in PS and may indicate a Th1 component in the early initial phase of AGEP.