Children with atopic dermatitis who carry toxin-positive Staphylococcus aureus strains have an expansion of blood CD5- B lymphocytes without an increase in disease severity

Abstract

Toxin-positive strains of Staphylococcus aureus (T + S. aureus) are present on the skin of some but not all patients with atopic dermatitis. Many staphylococcal toxins are superantigens, which can stimulate the immune response and thus may potentially lead to the very high levels of IgE characteristic of this condition, as well as exacerbating the clinical disease. The aim of this study was to determine whether the presence of T + S. aureus on the skin of children with atopic dermatitis was associated with in vivo evidence of a heightened humoral immune response, higher IgE levels and more severe clinical disease. Toxin gene expression in S. aureus isolated from the eczematous lesions of 28 children with atopic dermatitis was assessed by PCR. Clinical and immune data were also collected from this cohort. Thirteen of the 28 children (46%) were colonized with T + S. aureus strains. The presence of T + S. aureus was associated with a significant expansion in peripheral blood CD5- B cells (P = 0.01), and the more toxin types identified the greater the B-cell expansion (P = 0.002). However, in this cohort of children with atopic dermatitis, despite th in vivo expansion of B cells in children harbouring T + S. aureus, there was no associated increase in IgE levels or in clinical disease severity scores.

Fig. 1

Clinical severity of AD in children whose eczematous lesions were (+) or were not (–) colonized with toxin-producing staphylococci. Severity is assessed as percentage surface area affected (a) and dermatitis score (b). Horizontal line represents the medians.

Fig. 2

Absolute peripheral blood CD3⁺ T-lymphocyte (a), CD19⁺ B-lymphocyte (b), CD19⁺CD5⁻ B-lymphocyte (c) and CD19⁺CD5⁺ B-lymphocyte numbers (d) of children with AD whose skin was (+) or was not colonized (–) with toxin-producing staphylococci. Horizontal line represents the median. *P < 0·01. Lymphocyte subset results are unavailable for three of the 13 T⁺ group.

Fig. 3

Total serum IgE (a) and absolute peripheral blood eosinophil count (b) of children with AD whose eczematous lesions were (+) or were not (–) colonized with toxin-producing staphylococci. Horizontal line represents the median.