Foxp3 isoforms and IgE-mediated UVB-induced skin inflammation expression

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PROJECT SUMMARY Ultraviolet B light (UVB; 280-315nm) is a common environmental trigger that can induce skin inflammation and flares in several autoimmune diseases. UVB light is an established trigger for skin flares in SLE patients, and regional spikes in atmospheric UVB intensity correlate with flare frequency among SLE patients within that geographic region. In mice, IgE antibodies are elevated after UVB exposure, and previous work shows that skin-reactive IgE also plays a key role in removing damaged keratinocytes after carcinogen exposure. However, the role of self-reactive IgE has not been studied in photosensitivity reactions in autoimmunity. Regulatory T (Treg) cells play a central role in maintaining immune system homeostasis and modulating immune responses. Foxp3 is a master regulator of Treg development and function. FOXP3 mutations in patients with IPEX (Immunodysregulation, polyendocrinopathy, enteropathy, X-linked syndrome), which result in a deficiency in Tregs, result in lethal autoimmunity, similar to the disease observed in Foxp3 deficient mice. While highly conserved in both amino acid sequence and gene structure, one difference between humans and mice is that the human FOXP3 gene encodes two major alternatively spliced isoforms: a full-length version that uses all 10 exons (FOXP3FL, the only isoform in mice) and a shorter isoform lacking exon 2 (FOXP3∆E2). Recent studies have shown that Tregs from patients with some autoimmune diseases express increased levels of the ∆E2 isoform compared to those from healthy donors. Consistent with this finding, we have found that Tregs from SLE patients have increased expression of the FOXP3∆E2 isoform. To study the role of the ∆E2 isoform in Treg function we generated a new mouse strain with Foxp3 exon 2 deletion. Interestingly, we found that Foxp3∆E2 mice develop hallmark features of SLE, including anti-DNA and anti-nuclear autoantibodies, increased number and size of spontaneous germinal centers and kidney deposition of antibody complexes, by 4-5 weeks of age. Importantly, these mice display a marked increase in circulating IgE and develop IgE-specific autoantibodies against skin antigens, including Keratins 2 and 14. In addition, these mice have IgE deposits in the skin, which increase dramatically following UVB irradiation. Our central hypothesis is Foxp3DE2-expressing Tregs fail to regulate germinal center responses and promote IgE autoantibodies. To test this hypothesis, we will first determine the role of Foxp3∆Ex2-expressing Tregs in germinal center function, focusing on the relationship between Tfh and Tfr cells. Next, we will assess the role of autoreactive IgE in UVB-mediated skin inflammation in these mice. These studies will provide insights into the role of Foxp3∆E2 Treg function and the development and progression of inflammatory skin disease.