Infliximab induces downregulation of the IL-12/IL-23 axis in 6-sulfo-LacNac (slan)+ dendritic cells and macrophages

Abstract

Background: The spectrum of TNF-α-producing cells in patients with psoriasis, as well as their fate during treatment with TNF-α antagonists, is not clearly defined.

Objective: We sought to analyze the effects of anti-TNF-α treatment on TNF-α(+) cells in the skin and blood of patients with psoriasis.

Methods: Lesional psoriatic skin was analyzed by means of immunohistologic staining and quantitative RT-PCR, and peripheral blood cells were phenotypically characterized by means of multicolor immunofluorescence labeling.

Results: By using a tyramide-based signal amplification system, TNF-α was detected in dermal CD45(+)HLA-DR(+) leukocytes consisting of CD11c(+) dendritic cells and CD163(+) macrophages. In peripheral blood we observed an increase in the TNF-α-producing myeloid subsets of CD14(-) 6-sulfo-LacNac(+) dendritic cells and CD14(+)CD16(+) "intermediate" monocytes compared with healthy control subjects. Strikingly, we did not find detectable levels of TNF-α in other cells, including keratinocytes or T cells, making these cell types unlikely targets of TNF-α blockers. Up to 48 hours after the intravenous administration of the TNF-α antagonist infliximab, we encountered no overt changes in numbers of TNF-α(+) cells or signs of apoptosis in lesional psoriatic skin. Yet we observed a rapid decrease in IL-12p40, IL-1β, CCL20, and IL12RB1 mRNA levels. Consistently, TNF-α blockade during in vitro stimulation of 6-sulfo-LacNac DCs resulted in decreased production of IL-12 and IL-23 but not IL-6. In a mixed leukocyte reaction infliximab led to significantly decreased proliferation rates of T cells independent of the Fc antibody fragment.

Conclusion: The decrease in tissue inflammation during anti-TNF-α therapy is not due to immediate killing of TNF-α-producing cells but rather results from a rapid downregulation of the pathogenic IL-12/IL-23-driven immune response.

Keywords: 6-Sulfo-LacNac; 6-sulfo-LacNac; BDCA; Blood dendritic cell antigen; DC; Dendritic cell; IL-12p40; Inducible nitric oxide synthase; MACS; Magnetic cell sorting; Myeloid dendritic cell; NK; Natural killer; PASI; PMA; Phorbol 12-myristate 13-acetate; Psoriasis; Psoriasis Area and Severity Index; Soluble TNF-α (17 kDa); TNF receptor; TNF-α; TNFR; TUNEL; Terminal deoxynucleotidyl transferase dUTP nick end labeling; Transmembrane TNF-α (26 kDa); iNOS; mDC; myeloid dendritic cells; sTNF-α; slan; tmTNF-α.