Abstract
The skin of AD patients is often colonized by S. aureus strains that produce superantigens (SAg), primarily
staphylococcal enterotoxin B (SEB). There is a positive association between S. aureus skin colonization and
food allergy in AD. The mechanism of this association is unknown. We have made the observation that
epicutaneous (EC) application of ovalbumin (OVA) and SAg producer S. aureus, or OVA and SEB, results in the
selective exaggeration of anaphylaxis to oral challenge with OVA compared to EC application of OVA alone.
Moreover, it results in exaggerated systemic anaphylaxis to oral challenge with BSA-TNP in mice passively
sensitized with IgE anti-TNP, indicating that the enhancement of food anaphylaxis was non-antigen-specific and
determined by factors beyond differences in IgE Ab levels or affinity. We propose to dissect the mechanisms of
SEB enhancement of IgE mediated oral anaphylaxis.
Preliminary data show that enhanced susceptibility to oral anaphylaxis in mice EC exposed to OVA+SEB
is associated with elevated levels of serum IL-4, dependent on IL-4 and IL-4R¿ expression by intestinal epithelial
cells (IECs),and accompanied by increased intestinal permeability (IP). Enhanced susceptibility is inhibited by
Divertin, a small molecule that suppresses intestinal absorption of antigen via the paracellular pathway by
blocking the recruitment of myosin light chain kinase (MLCK) to the peri-junctional actinomyosin ring, where it
disrupts epithelial tight junctions. This suggests a critical role for MLCK in food allergy. In addition, the data show
that EC application of SEB causes a massive influx of basophils in skin-draining lymph nodes (dLNs) that was
dependent on CD40 keratinocyte (KC)-derived IL-33, and T cells. The recruited basophils enhanced the ability
of dendritic cells (DCs) from skin dLNs to drive Th2 polarization. Pretreatment of DCs in vitro with IL-4 also
promoted their capacity to drive Th2 polarization.
We propose to test the hypothesis that SEB from S. aureus that colonizes AD skin binds to CD40 on KCs
and triggers caspase 8 mediated cleavage and release of bioactive IL-33 which induces IL-3 release by T cells
leading to recruitment of basophils in dLNs. There, basophil-derived IL-4 promotes the Th2 polarizing ability of
DCs that have captured antigen encountered in the skin. These events drive a rise in systemic levels of Th2
derived IL-4. Increased IL-4 signaling in IECs synergizes with mediators released by MCs to promote MLCK
dependent barrier loss by causing redistribution of tight junction proteins. The resulting increased antigen
absorption triggers a forward amplification cycle of MC activation that exaggerates allergy to foods against which
the patient has been sensitized.
The studies proposed will define the mechanisms by which S. aureus skin colonization aggravates food
allergy and will uncover a central role of MLCK in this disease. They may lead to novel therapies for food allergy
that would target S. aureus skin colonization, CD40 in skin, IL-33 and MLCK.