Failure of Etanercept and Methotrexate Combination Therapy to Surpass Etanercept Monotherapy in Psoriatic Arthritis—What About the Joint Counts? Comment on the Article by Mease et al

Abstract

activating a potent interferonmediated response. Moreover, LL37 can also act as self antigen, activating HLA–C*06:02restricted autoreactive T cells, mainly CD8 cells (3) as well as B cells (by a lesserknown mechanism). Recent data suggest that the humoral response against LL37 characterizes PsA development in subjects with psoriasis (4,5). Lande and colleagues demonstrated levels of anti–native LL37 in PsA synovial fluid correlated with disease activity (4); a humoral response against citrullinated and carbamylated LL37 was more prevalent in PsA sera. Testing a large panel of putative selfantigens, Yuan and colleagues found an autoimmunelike autoantibody profile in psoriasis (5); more interestingly, levels of anti–native LL37 antibodies were able to discriminate patients with PsA versus those without PsA. We analyzed serum samples from 38 patients with psoriasis and PsA who fulfilled the Classification of Psoriatic Arthritis Study Group criteria for PsA (1) (55% female, median age 50 years [interquartile range 42–55], 50% with a disease duration of >5 years, and 13% with axial involvement), 8 patients with psoriasis only (75% female, median age 45 years [interquartile range 28–72 years]), and 41 healthy subjects (71% female, median age 50 years [interquartile range 43–64 years]). Anti–LL37 IgG antibodies were detected by indirect enzymelinked immunosorbent assay developed inhouse using recombinant LL37 (Biosyntesis). Sera were considered positive for anti–LL37 IgG if levels were >0.7314 (2 SD above the mean in healthy subjects). Peripheral blood mononuclear cells (PBMCs) from 2 patients with PsA (1 positive and 1 negative for anti–LL37 antibodies) were cultured with 10 ng/ml of interleukin2 (IL2), 50 ng/ml of IL21, and 100 ng/ml of BAFF (Miltenyi) in the presence of 10 μg/ml of LL37 or nonspecific T and B cell stimulators (50 ng/ml of phorbol myristate acetate, 1 μg/ml of ionomycin [Sigma Aldrich], and 1 μg/ml of CD40L [Miltenyi]). PBMCs were harvested after 1 day and 7 days of culture and stained with BV650conjugated CD3 (BioLegend), phycoerythrin (PE)–Cy7–conjugated CD69 (BD Biosciences), allophycocyanin–conjugated CD154 (BD Biosciences), BV570conjugated CD19 (BioLegend), and PECF594–conjugated CD86 (BD Biosciences). Cellular populations were acquired on Fortessa BD flow cytometer, and results were analyzed with FlowJo. Anti–LL37 antibodies were detected in 8 of 38 PsA serum samples (21%) compared to none of the healthy subjects (P < 0.01 by MannWhitney test) or patients with psoriasis only (P = 0.004 by MannWhitney test). Regardless of anti–LL37 presence, significant B cell activation (Figures 1A and C) and T cell activation (Figures 1B and D) was noted at 24 hours after LL37 stimulation in PsA patients. However, in the patient with anti–LL37 positivity, B cell activation (Figure 1A) and T cell activation (Figure 1B) was more pronounced together with increased expression of the costimulatory molecule CD154 (CD40L) on CD4 T cells (Figure 1E) compared to the patient without anti–LL-37 positivity (Figures 1C, 1D, and 1F), which supports the notion of a T cell–dependent mechanism of humoral response in PsA, similar to what is observed in classic autoimmune diseases. Taken together, our data support the importance of LL37 in the pathogenesis of PsA and suggest that this effect may go beyond serum antibody status and be based on a T cell–dependent process.