Dermal injection of immunocytes induces psoriasis

Area of Science:

• Dermatology
• Immunology
• Pathophysiology

Background:

• Psoriasis pathogenesis involves complex interactions between keratinocytes, immune cells, and endothelial cells.
• Lack of a suitable animal model has hindered understanding of causal relationships in psoriasis.
• Key question: Is psoriasis a primary disorder of keratinocytes or the immune system?

Purpose of the Study:

• To investigate the primary cause of psoriasis: keratinocyte dysfunction versus immune system dysregulation.
• To establish a causal link between specific cell types and psoriasis development using a novel model.

Main Methods:

• Developed an experimental system using orthotopically transferred human skin onto immunodeficient mice.
• Injected autologous immunocytes (blood-derived immune cells) into dermis of psoriasis-associated (PN) and normal (NN) skin grafts.
• Analyzed resulting skin phenotypes using clinical, histological, and immunophenotypic methods.

Main Results:

• Injection of activated autologous immunocytes converted all PN skin samples into psoriatic plaques.
• Resultant plaques exhibited characteristic psoriatic features: thickening, flaking, epidermal T-cell infiltration, and altered rete pegs.
• NN skin samples did not develop psoriatic plaques, indicating the importance of the original skin's predisposition.

Conclusions:

• Psoriasis is primarily driven by pathogenetic blood-derived immunocytes.
• These immunocytes induce secondary activation and disordered growth of endogenous keratinocytes and vascular endothelial cells.
• The study establishes a causal role for the immune system in initiating psoriasis.