Deficiency in immunoglobulin G2 antibodies against staphylococcal enterotoxin C1 defines a subgroup of patients with atopic dermatitis

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Abstract
Background and aim Atopic dermatitis (AD) is a common chronic inflammatory skin disease often accompanied by cutaneous Staphylococcus aureus colonization and, in this regard, especially complicated by the presence of superantigen‐producing strains. Because IgG antibodies comprise an important defence mechanism of the adaptive immune system against bacteria, it was investigated whether AD patients have an abnormal pattern or distribution of superantigen‐specific IgG subclass antibodies in association with disease severity and activity. Methods Staphylococcal enterotoxin B (SEB) and staphylococcal enterotoxin C1 (SEC1) specific IgG antibody subclasses were assessed in n=89 adult AD patients with mild to severe disease activity as determined by the SCORAD score and in n=28 healthy age‐matched controls. Results were correlated with the current status of bacterial skin colonization and severity score. Results Thirty‐eight per cent of the AD patients showed a selective deficiency in IgG2 antibodies against SEC1 compared with only 14% in the control group. The absence of these antibodies was found in both currently colonized and non‐colonized AD patients and was associated with a severe phenotype (SCORAD more than 40 points in two‐thirds of the deficient patients). However, these patients had normal production levels of IgG2 antibodies against pneumococcal capsular polysaccharide (PCP) and SEB, but higher IgG1 and IgG4 titres against SEC1. Except for elevated total IgG1, total IgG subclass levels were normal in this AD subgroup. Yet, peripheral blood mononuclear cells (PBMCs) derived from these patients clearly produced IL‐4 and IL‐5 upon SEC1 re‐stimulation whereas PBMCs from those providing SEC1‐specific IgG2 antibodies failed in the production of these cytokines. Conclusion A subgroup of AD patients suffers from a selective deficiency to produce anti‐SEC1 IgG2 antibodies. This patient group is characterized by a severe AD phenotype.