Unable to isolate sufficient cells from the skin biopsy to perform study experiments.

IFN-gamma is a central player in the development of psoriasis lesions, which can be involved a variety of cellular processes in the skin. Dendritic cells are important cells in driving inflammation in psoriasis through the induction of T cells that produce IL-17 in psoriasis. Injecting IFN-g into the skin can increase the numbers of T cells and also inflammatory DCs that produce cytokines involved in IL-17 production. Thus, the investigators hypothesize that the dendritic cells present in the skin after IFN-g injection polarize IL-17-producing T cells.

Inclusion Criteria:

• Signed informed consent
• Normal volunteers with no evidence of skin disease OR diagnosis of plaque type psoriasis for at least 6 months
• 18 years of age or greater
• For women of childbearing potential or in men whose partners may become pregnant, willingness to use an acceptable method of contraception to prevent pregnancy for the duration of the study. Acceptable methods of contraception include use of a condom; abstinence; use by sexual partner of oral implantable or injectable contraceptives, IUD, female condom, diaphragm with spermicide, cervical cap; or a sterile sexual partner

Exclusion Criteria:

• Guttate, erythrodermic, or pustular psoriasis as sole or predominant form of psoriasis
• Clinically significant psoriasis flare during screening or on the first treatment day
• Hypersensitivity to IFN-g or E. coli derivatives
• Pre-existing, uncontrolled myelosuppression, cardiac disease, seizure disorders, compromised central nervous system function or multiple sclerosis
• History of malignancy, clinically significant renal insufficiency, poorly controlled medical conditions that would increase the risks
• Presence of malignancy within the past 5 years, including lymphoproliferative disorders. Subjects with a history of fully resolved basal cell or squamous cell skin cancer may be enrolled.
• Pregnancy or lactation. As the risk of IFN-g in pregnancy is unknown, pregnant women will be excluded from the study.
• Any medical condition that, in the judgment of the investigator, would jeopardize the subject's safety following exposure to study drug