Staphylococcal TSST-1 Association with Eczema Herpeticum in Humans

Abstract

Atopic dermatitis (AD) is a condition affecting 30 million persons in the United States. AD patients are heavily infected with Staphylococcus aureus on the skin. A particularly severe form of AD is eczema herpeticum (ADEH), where the patients' AD is complicated by S. aureus and herpes simplex virus (HSV) infection. This study examined the S. aureus strains from 15 ADEH patients, provided blinded, and showed a high association of ADEH with strains that produce toxic shock syndrome toxin-1 (TSST-1; 73%) compared to 10% production by typical AD isolates from patients without EH and those from another unrelated condition, cystic fibrosis. The ADEH isolates produced the superantigens associated with TSS (TSST-1 and staphylococcal enterotoxins A, B, and C). This association may in part explain the potential severity of ADEH. We also examined the effect of TSST-1 and HSV-1 on human epithelial cells and keratinocytes. TSST-1 used CD40 as its receptor on epithelial cells, and HSV-1 either directly or indirectly interacted with CD40. The consequence of these interactions was chemokine production, which is capable of causing harmful inflammation, with epidermal/keratinocyte barrier disruption. Human epithelial cells treated first with TSST-1 and then HSV-1 resulted in enhanced chemokine production. Finally, we showed that TSST-1 modestly increased HSV-1 replication but did not increase viral plaque size. Our data suggest that ADEH is associated with production of the major TSS-associated superantigens, together with HSV reactivation. The superantigens plus HSV may damage the skin barrier by causing harmful inflammation, thereby leading to increased symptoms. IMPORTANCE Atopic dermatitis (eczema, AD) with concurrent herpes simplex virus infection (eczema herpeticum, ADEH) is a severe form of AD. We show that ADEH patients are colonized with Staphylococcus aureus that primarily produces the superantigen toxic shock syndrome toxin-1 (TSST-1); however, significantly but to a lesser extent the superantigens staphylococcal enterotoxins A, B, and C are also represented in ADEH. Our studies showed that TSST-1 uses the immune costimulatory molecule CD40 as its epithelial cell receptor. Herpes simplex virus (HSV) also interacted directly or indirectly with CD40 on epithelial cells. Treatment of epithelial cells with TSST-1 and then HSV-1 resulted in enhanced chemokine production. We propose that this combination of exposures (TSST-1 and then HSV) leads to opening of epithelial and skin barriers to facilitate potentially serious ADEH.

Keywords: CD40; Staphylococcus aureus; atopic dermatitis; chemokines; eczema; eczema herpeticum; epithelial cells; herpes simplex virus; staphylococcal enterotoxins; toxic shock syndrome toxin 1.

FIG 1

CD40 dependence of IL-8 production in TSST-1-treated and HSV-1-infected human vaginal epithelial cells (CD40 wild type [WT], CD40 CRISPR/Cas9 knockout [KO], and HVECs complemented with CD40 on a plasmid [Comp]). Human vaginal epithelial cells were cultured in triplicate in 96-well flat-bottom tissue culture dishes until confluent. Then, the medium was changed to keratinocyte serum-free medium (KSFM) with TSST-1 or HSV-1. Incubation was continued for 6 additional h, and the plate was frozen at −20°C to lyse cells. Subsequently, IL-8 concentrations in supernatants were determined by enzyme-linked immunosorbent assay (ELISA). Data are reported as means ± SD as a percentage of wild-type value.

FIG 2

TSST-1 followed by HSV-1 induces chemokine production (IL-8) by human keratinocytes. Human keratinocytes were incubated until confluent in 96-well flat-bottom tissue culture plates in KSFM. Subsequently, the medium was changed and TSST-1 (T) and HSV-1 (H) were added to wells in triplicate as indicated. The numbers in parentheses indicate time in hours before or after treatment with TSST-1. The cells were incubated for a total of 6 h after time zero at 37°C, 5% CO₂. Then, the plate was frozen at −20°C to lyse cells. IL-8, as a representative chemokine, was then measured by ELISA. Data reported as means ± SD.

FIG 3

TSST-1 effects on HSV-1 growth and spread in keratinocytes. (A) Multistep growth of HSV-1(F) on HaCaT keratinocyte cultures that were untreated (No TSST) or treated with 10 μg/ml TSST-1 beginning 1 h before initiation of infection (Pre-TSST) or 2 h after initiation of infection (Post-TSST). (B) Data from the experiment shown in panel A at 24 h after initiation of infection demonstrated enhanced HSV-1 production after TSST treatment (P < 0.05). n.s., not significant. (C) Spread of HSV-1(F) on HaCaT cells treated with 10 μg/ml TSST-1 beginning 2 h after initiation of infection.

FIG 4

Model for the association of TSST-1 with ADEH.