TNF and psoriasis: Indeed, the histologic analysis not only of the digit skin (Figures 3A and 4A), but also of the irritated dorsal skin distal from toes (Figure 3E) showed clear signs of inflammation on doxycycline induction, and the amount of human TNFα mRNA induced in dorsal, abdominal, or paw skin samples correlated highly with levels of the cytokine IL-23 (Figure 3F), which is typically up-regulated during psoriasis (19).