In vitro screening for putative psoriasis-specific antigens among wheat proteins and peptides

Background Patients with psoriasis who had raised IgG and/or IgA antigliadin antibodies showed clinical improvement in a trial with a gluten-free diet. The selection of patients for the diet treatment was based on the presence of specific antibodies, i.e. the result of humoral immunity. Objectives As psoriasis is now considered to be a T cell-mediated disease we decided to challenge peripheral blood mononuclear cells (PBMCs) in vitro from randomly selected patients with well-defined wheat proteins/peptides to explore the possibility of identifying a specific antigen with T cell activating properties in a subgroup of patients. Methods PBMCs from 37 patients (20 female and 17 male; mean age 49 years) and 37 healthy controls (12 female and 25 male; mean age 57 years) were included. Not all patients participated in all experiments. The PBMCs were exposed in vitro with the following wheat proteins/peptides in various concentrations: total albumins, 0.28 alpha-amylase inhibitor and the synthetic peptides, p31-43, p57-68 and p62-75, based on coeliac-active sequences of alpha-gliadin. The proliferative response was measured as counts per minute after the cells had been pulsed with methyl-H-3-thymidine. Results Albumin, alpha-amylase inhibitor, p31-43 and p57-68 elicited a significant response in both patients and controls but showed no differences between the groups. The response induced by the alpha-amylase inhibitor was higher than that induced by the albumin fraction and the p31-43 and p57-68 peptides. At a concentration of 25 mu g mL(-1), five of 36 patients with psoriasis responded positively to the p62-75 peptide and none of the 33 controls, using a stimulation index of 2.4 as the cut-off level (P < 0.05). These five patients did not show clinical features that differed from the remaining patients. Among the responding patients the relative number of CD4+ cells increased in some but not all after in vitro challenge with the albumins, 0.28 alpha-amylase inhibitor, and p62-75. These antigens could also induce in vitro the expression of the homing antigen cutaneous lymphocyte antigen (CLA) in a few patients and controls. Conclusions The wheat protein antigens, especially the p62-75 peptide, might be of interest in a subgroup of patients with psoriasis.