The Genetics of Eczema Herpeticum.

Eczema herpeticum (EH) is a viral skin infection caused by herpes simplex virus (HSV) superimposed on eczematous skin lesions in atopic dermatitis (AD). Though the pathogenesis of EH has yet to be fully elucidated, the fact that EH is relatively rare despite a majority of adults showing serologic evidence of HSV exposure points to a genetic component predisposing to the disease. A number of genetic variants have been isolated in EH which may help distinguish a subgroup of patients susceptible to developing the condition. These unique genetic characteristics include deficiencies in skin barrier function and hydration, as well as at the level of the immune system. In this review, we summarize the genetic findings associated with EH identified to date. Isolating genetic markers in EH will be instrumental in stratifying patients at risk for EH and will have significant implications in the development and tailoring of targeted therapies.

Signaling sphingolipids are biomarkers for atopic dermatitis prone to disseminated viral infections.

BACKGROUND: Life-threatening viral diseases such as eczema herpeticum (EH) and eczema vaccinatum (EV) occur in <5% of individuals with atopic dermatitis (AD). The diagnosis of AD, however, excludes all individuals with AD from smallpox vaccination. OBJECTIVES: We sought to identify circulatory and skin lipid biomarkers associated with EH and EV. METHODS: Stratum corneum and plasma samples from 15 subjects with AD and a history of EH, 13 age- and gender-matched subjects with AD and without EH history, and 13 healthy nonatopic (NA) controls were analyzed by liquid chromatography tandem mass spectrometry for sphingolipid content. Sphingosine-1-phosphate (S1P) and ceramide levels were validated in plasma samples from the Atopic Dermatitis Vaccinia Network/Atopic Dermatitis Research Network repository (12 NA, 12 AD, 23 EH) and plasma from 7 subjects with EV and 7 matched subjects with AD. S1P lyase was downregulated in human primary keratinocytes to evaluate its effect on herpes simplex virus 1 (HSV-1) replication in vitro. RESULTS: The stratum corneum of patients with EH demonstrated significantly higher levels of free sphingoid bases than those in patients who were NA, indicating enhanced sphingolipid turnover in keratinocytes (P < .05). Plasma from 2 independent cohorts of patients with EH had a significantly increased S1P/ceramide ratio in subjects with EH versus those with AD and or who were NA (P < .01). The S1P level in plasma from subjects with EV was twice the level in plasma from subjects with AD (mean = 1,533 vs 732 pmol/mL; P < .001). Downregulation of S1P lyase expression with silencing RNA led to an increased S1P level and doubled HSV-1 titer in keratinocytes. CONCLUSIONS: Our data point to long-term abnormalities in the S1P signaling system as a biomarker for previous disseminated viral diseases and a potential treatment target in recurring infections.

Whole genome sequencing identifies novel genetic mutations in patients with eczema herpeticum.

BACKGROUND: Eczema herpeticum (EH) is a rare complication of atopic dermatitis (AD) caused by disseminated herpes simplex virus (HSV) infection. The role of rare and/or deleterious genetic variants in disease etiology is largely unknown. This study aimed to identify genes that harbor damaging genetic variants associated with HSV infection in AD with a history of recurrent eczema herpeticum (ADEH+). METHODS: Whole genome sequencing (WGS) was performed on 49 recurrent ADEH+ (≥3 EH episodes), 491 AD without a history of eczema herpeticum (ADEH-) and 237 non-atopic control (NA) subjects. Variants were annotated, and a gene-based approach (SKAT-O) was used to identify genes harboring damaging genetic variants associated with ADEH+. Genes identified through WGS were studied for effects on HSV responses and keratinocyte differentiation. RESULTS: Eight genes were identified in the comparison of recurrent ADEH+to ADEH-and NA subjects: SIDT2, CLEC7A, GSTZ1, TPSG1, SP110, RBBP8NL, TRIM15, and FRMD3. Silencing SIDT2 and RBBP8NL in normal human primary keratinocytes (NHPKs) led to significantly increased HSV-1 replication. SIDT2-silenced NHPKs had decreased gene expression of IFNk and IL1b in response to HSV-1 infection. RBBP8NL-silenced NHPKs had decreased gene expression of IFNk, but increased IL1b. Additionally, silencing SIDT2 and RBBP8NL also inhibited gene expression of keratinocyte differentiation markers keratin 10 (KRT10) and loricrin (LOR). CONCLUSION: SIDT2 and RBBP8NL participate in keratinocyte's response to HSV-1 infection. SIDT2 and RBBP8NL also regulate expression of keratinocyte differentiation genes of KRT10 and LOR.

Replicated methylation changes associated with eczema herpeticum and allergic response.

BACKGROUND: Although epigenetic mechanisms are important risk factors for allergic disease, few studies have evaluated DNA methylation differences associated with atopic dermatitis (AD), and none has focused on AD with eczema herpeticum (ADEH+). We will determine how methylation varies in AD individuals with/without EH and associated traits. We modeled differences in genome-wide DNA methylation in whole blood cells from 90 ADEH+, 83 ADEH-, and 84 non-atopic, healthy control subjects, replicating in 36 ADEH+, 53 ADEH-, and 55 non-atopic healthy control subjects. We adjusted for cell-type composition in our models and used genome-wide and candidate-gene approaches. RESULTS: We replicated one CpG which was significantly differentially methylated by severity, with suggestive replication at four others showing differential methylation by phenotype or severity. Not adjusting for eosinophil content, we identified 490 significantly differentially methylated CpGs (ADEH+ vs healthy controls, genome-wide). Many of these associated with severity measures, especially eosinophil count (431/490 sites). CONCLUSIONS: We identified a CpG in IL4 associated with serum tIgE levels, supporting a role for Th2 immune mediating mechanisms in AD. Changes in eosinophil level, a measure of disease severity, are associated with methylation changes, providing a potential mechanism for phenotypic changes in immune response-related traits.

Defective natural killer cell activity in a mouse model of eczema herpeticum.

BACKGROUND: Patients with atopic dermatitis (AD) are susceptible to several viruses, including herpes simplex virus (HSV). Some patients experience 1 or more episodes of a severe skin infection caused by HSV termed eczema herpeticum (EH). There are numerous mouse models of AD, but no established model exists for EH. OBJECTIVE: We sought to establish and characterize a mouse model of EH. METHODS: We infected AD-like skin lesions with HSV1 to induce severe skin lesions in a dermatitis-prone mouse strain of NC/Nga. Gene expression was investigated by using a microarray and quantitative PCR; antibody titers were measured by means of ELISA; and natural killer (NK) cell, cytotoxic T-cell, regulatory T-cell, and follicular helper T-cell populations were evaluated by using flow cytometry. The role of NK cells in HSV1-induced development of severe skin lesions was examined by means of depletion and adoptive transfer. RESULTS: Inoculation of HSV1 induced severe erosive skin lesions in eczematous mice, which had an impaired skin barrier, but milder lesions in small numbers of normal mice. Eczematous mice exhibited lower NK cell activity but similar cytotoxic T-cell activity and humoral immune responses compared with normal mice. The role of NK cells in controlling HSV1-induced skin lesions was demonstrated by experiments depleting or transferring NK cells. CONCLUSION: A murine model of EH with an impaired skin barrier was established in this study. We demonstrated a critical role of defective NK activities in the development of HSV1-induced severe skin lesions in eczematous mice.

Targeted deep sequencing identifies rare loss-of-function variants in IFNGR1 for risk of atopic dermatitis complicated by eczema herpeticum.

BACKGROUND: A subset of atopic dermatitis is associated with increased susceptibility to eczema herpeticum (ADEH+). We previously reported that common single nucleotide polymorphisms (SNPs) in the IFN-γ (IFNG) and IFN-γ receptor 1 (IFNGR1) genes were associated with the ADEH+ phenotype. OBJECTIVE: We sought to interrogate the role of rare variants in interferon pathway genes for the risk of ADEH+. METHODS: We performed targeted sequencing of interferon pathway genes (IFNG, IFNGR1, IFNAR1, and IL12RB1) in 228 European American patients with AD selected according to their eczema herpeticum status, and severity was measured by using the Eczema Area and Severity Index. Replication genotyping was performed in independent samples of 219 European American and 333 African American subjects. Functional investigation of loss-of-function variants was conducted by using site-directed mutagenesis. RESULTS: We identified 494 single nucleotide variants encompassing 105 kb of sequence, including 145 common, 349 (70.6%) rare (minor allele frequency <5%), and 86 (17.4%) novel variants, of which 2.8% were coding synonymous, 93.3% were noncoding (64.6% intronic), and 3.8% were missense. We identified 6 rare IFNGR1 missense variants, including 3 damaging variants (Val14Met [V14M], Val61Ile, and Tyr397Cys [Y397C]) conferring a higher risk for ADEH+ (P = .031). Variants V14M and Y397C were confirmed to be deleterious, leading to partial IFNGR1 deficiency. Seven common IFNGR1 SNPs, along with common protective haplotypes (2-7 SNPs), conferred a reduced risk of ADEH+ (P = .015-.002 and P = .0015-.0004, respectively), and both SNP and haplotype associations were replicated in an independent African American sample (P = .004-.0001 and P = .001-.0001, respectively). CONCLUSION: Our results provide evidence that both genetic variants in the gene encoding IFNGR1 are implicated in susceptibility to the ADEH+ phenotype.

Filaggrin deficiency promotes the dissemination of cutaneously inoculated vaccinia virus.

BACKGROUND: Eczema vaccinatum is a life-threatening complication of smallpox vaccination in patients with atopic dermatitis (AD) characterized by dissemination of vaccinia virus (VV) in the skin and internal organs. Mutations in the filaggrin (FLG) gene, the most common genetic risk factor for AD, confer a greater risk for eczema herpeticum in patients with AD, suggesting that it impairs the response to cutaneous viral infections. OBJECTIVE: We sought to determine the effects of FLG deficiency on the response of mice to cutaneous VV inoculation. METHODS: VV was inoculated by means of scarification of unsensitized skin or skin topically sensitized with ovalbumin in FLG-deficient flaky tail (ft/ft) mice or wild-type (WT) control mice. The sizes of primary and satellite skin lesions were measured, and hematoxylin and eosin staining was performed. VV genome copy numbers and cytokine mRNA levels were measured by using quantitative PCR. RESULTS: VV inoculation in unsensitized skin of ft/ft mice, independent of the matted hair mutation, resulted in larger primary lesions, more abundant satellite lesions, heavier viral loads in internal organs, greater epidermal thickness, dermal cellular infiltration, and higher local Il17a, Il4, Il13, and Ifng mRNA levels than in WT control mice. VV inoculation at sites of topical ovalbumin application amplified all of these features in ft/ft mice but had no detectable effect in WT control mice. The number of satellite lesions and the viral loads in internal organs after cutaneous VV inoculation were significantly reduced in both unsensitized and topically sensitized ft/ftxIl17a(-/-) mice. CONCLUSION: FLG deficiency predisposes to eczema vaccinatum. This is mediated primarily through production of IL-17A.

Identification of novel gene signatures in patients with atopic dermatitis complicated by eczema herpeticum.

BACKGROUND: A subset of patients with atopic dermatitis (AD) is prone to disseminated herpes simplex virus (HSV) infection (ie, atopic dermatitis with a history of eczema herpeticum [ADEH+]). Biomarkers that identify ADEH+ are lacking. OBJECTIVE: We sought to search for novel ADEH+ gene signatures in PBMCs. METHODS: An RNA-sequencing approach was applied to evaluate global transcriptional changes by using PBMCs from patients with ADEH+ and patients with atopic dermatitis without a history of eczema herpeticum (ADEH-). Candidate genes were confirmed by means of quantitative PCR or ELISA. RESULTS: PBMCs from patients with ADEH+ had distinct changes to the transcriptome when compared with those from patients with ADEH- after HSV-1 stimulation: 792 genes were differentially expressed at a false discovery rate of less than 0.05 (ANOVA), and 15 type I and type III interferon genes were among the top 20 most downregulated genes in patients with ADEH+. We further validated that IFN-α and IL-29 mRNA and protein levels were significantly decreased in HSV-1-stimulated PBMCs from patients with ADEH+ compared with those from patients with ADEH- and healthy subjects. Ingenuity Pathway Analysis demonstrated that the upstream regulators of type I and type III interferons, interferon regulatory factor (IRF) 3 and IRF7, were significantly inhibited in patients with ADEH+ based on the downregulation of their target genes. Furthermore, we found that gene expression of IRF3 and IRF7 was significantly decreased in HSV-1-stimulated PBMCs from patients with ADEH+. CONCLUSIONS: PBMCs from patients with ADEH+ have a distinct immune response after HSV-1 exposure compared with those from patients with ADEH-. Inhibition of the IRF3 and IRF7 innate immune pathways in patients with ADEH+ might be an important mechanism for increased susceptibility to disseminated viral infection.

IL-10 suppresses IL-17-mediated dermal inflammation and reduces the systemic burden of Vaccinia virus in a mouse model of eczema vaccinatum.

Individuals with atopic dermatitis (AD) are susceptible to a severe, potentially fatal, systemic infection and inflammatory response following exposure to Vaccinia virus (VV). IL-10 acts both as an inducer of Th2 responses and as a regulator of T cell activation. It has been shown to limit skin inflammation elicited by contact sensitizers. AD exacerbations have been associated with decreased IL-10 function. We used IL-10(-/-) mice to test the role of the cytokine in VV immunity. They exhibited larger primary lesions and increased cutaneous neutrophil infiltration compared to wild-type (WT) counterparts. This was associated with enhanced production of IL-17A, IL-17F and CXCL2. Paradoxically, despite intact adaptive immune responses, tissue viral burdens were increased in IL-10(-/-) mice. These findings suggest that IL-10 is important in limiting skin inflammation induced by VV and that abnormal IL-17-driven neutrophil recruitment at the primary infection site in the skin results in increased systemic viral dissemination.

Genetic variants in interferon regulatory factor 2 (IRF2) are associated with atopic dermatitis and eczema herpeticum.

Interferon regulatory factor 2 (IRF2) is a member of a family of transcriptional factors involved in the modulation of IFN-induced immune responses to viral infection. To test whether genetic variants in IRF2 predict risk of atopic dermatitis (AD) and ADEH (atopic dermatitis complicated by eczema herpeticum), we genotyped 78 IRF2 tagging single-nucleotide polymorphisms (SNPs) in both European-American (n = 435) and African-American (n = 339) populations. Significant associations were observed between AD and two SNPs (rs793814, P = 0.007, odds ratio (OR) = 0.52; rs3756094, P = 0.037, OR = 0.66) among European Americans and one SNP (rs3775572, P = 0.016, OR = 0.46) among African Americans. Significant associations were also observed between ADEH and five SNPs (P = 0.049-0.022) among European Americans. The association with ADEH was further strengthened by haplotype analyses, wherein a five-SNP (CAGGA) haplotype showed the strongest association with ADEH (P = 0.0008). Eight IRF2 SNPs were significantly associated with IFN-γ production after herpes simplex virus (HSV) stimulation (P = 0.048-0.0008), including an AD-associated SNP (rs13139310, P = 0.008). Our findings suggest that distinct markers in IRF2 may be associated with AD and ADEH, which may depend upon ethnic ancestry, and genetic variants in IRF2 may contribute to an abnormal immune response to HSV.

The signal transducer and activator of transcription 6 gene (STAT6) increases the propensity of patients with atopic dermatitis toward disseminated viral skin infections.

BACKGROUND: Atopic dermatitis (AD) is a chronic inflammatory skin disease associated with increased susceptibility to recurrent skin infections. OBJECTIVE: We sought to determine why a subset of patients with AD have an increased risk of disseminated viral skin infections. METHODS: Human subjects with AD with a history of eczema herpeticum (EH) and various control groups were enrolled. Vaccinia virus (VV) expression was measured by means of PCR and immunofluorescent staining in skin biopsy specimens from each study group after incubation with VV. Transgenic mice with a constitutively active signal transducer and activator of transcription 6 gene (STAT6) were characterized for response to VV skin inoculation. Genotyping for 10 STAT6 single nucleotide polymorphisms (SNPs) was performed in a white patient sample (n = 444). RESULTS: VV gene and protein expression were significantly increased in the skin of patients with EH compared with other subject groups after incubation with VV in vitro. Antibody neutralization of IL-4 and IL-13 resulted in lower VV replication in patients with a history of EH. Mice that expressed a constitutively active STAT6 gene compared with wild-type mice had increased mortality and satellite lesion formation after VV skin inoculation. Significant associations were observed between STAT6 SNPs and EH (rs3024975, rs841718, rs167769, and rs703817) and IFN-γ production. The strongest association was observed for a 2-SNP haplotype (patients with AD with a history of EH vs patients with AD without a history of EH, 24.9% vs 9.2%; P = 5.17 × 10(-6)). CONCLUSION: The STAT6 gene increases viral replication in the skin of patients with AD with a history of EH. Further genetic association studies and functional investigations are warranted.

Human atopic dermatitis complicated by eczema herpeticum is associated with abnormalities in IFN-γ response.

BACKGROUND: The basis for increased susceptibility of patients with atopic dermatitis (AD) to develop disseminated viral skin infections such as eczema herpeticum (AD with a history of eczema herpeticum, ADEH(+)) is poorly understood. OBJECTIVE: We sought to determine whether subjects with AD prone to disseminated viral skin infections have defects in their IFN responses. METHODS: GeneChip profiling was used to identify differences in gene expression of PBMCs from patients with ADEH(+) compared with patients with AD without a history of eczema herpeticum (ADEH(-)) and nonatopic controls. Key differences in protein expression were verified by enzyme-linked immunosorbent spot assay and/or ELISA. Clinical relevance was further demonstrated by a mouse model of disseminated viral skin infection and genetic association analysis for genetic variants in IFNG and IFNGR1 and ADEH among 435 cases and controls. RESULTS: We demonstrate by global gene expression analysis selective transcriptomic changes within the IFN superfamily of PBMCs from subjects with ADEH(+) reflecting low IFN-γ and IFN-γ receptor gene expression. IFN-γ protein production was also significantly lower in patients with ADEH(+) (n = 24) compared with patients with ADEH(-) (n = 20) and nonatopic controls (n = 20). IFN-γ receptor knockout mice developed disseminated viral skin infection after epicutaneous challenge with vaccinia virus. Genetic variants in IFNG and IFNGR1 single nucleotide polymorphisms (SNPs) were significantly associated with ADEH (112 cases, 166 controls) and IFN-γ production: a 2-SNP (A-G) IFNGR1 haplotype (rs10457655 and rs7749390) showed the strongest association with a reduced risk of ADEH+ (13.2% ADEH(+) vs 25.5% ADEH(-); P = .00057). CONCLUSION: Patients with ADEH(+) have reduced IFN-γ production, and IFNG and IFNGR1 SNPs are significantly associated with ADEH(+) and may contribute to an impaired immune response to herpes simplex virus.

Filaggrin mutations that confer risk of atopic dermatitis confer greater risk for eczema herpeticum.

BACKGROUND: Loss-of-function null mutations R501X and 2282del4 in the skin barrier gene, filaggrin (FLG), represent the most replicated genetic risk factors for atopic dermatitis (AD). Associations have not been reported in African ancestry populations. Atopic dermatitis eczema herpeticum (ADEH) is a rare but serious complication of AD resulting from disseminated cutaneous herpes simplex virus infections. OBJECTIVE: We aimed to determine whether FLG polymorphisms contribute to ADEH susceptibility. METHODS: Two common loss-of-function mutations plus 9 FLG single nucleotide polymorphisms were genotyped in 278 European American patients with AD, of whom 112 had ADEH, and 157 nonatopic controls. Replication was performed on 339 African American subjects. RESULTS: Significant associations were observed for both the R501X and 2282del4 mutations and AD among European American subjects (P = 1.46 x 10(-5), 3.87 x 10(-5), respectively), but the frequency of the R501X mutation was 3 times higher (25% vs 9%) for ADEH than for AD without eczema herpeticum (EH) (odds ratio [OR], 3.4; 1.7-6.8; P = .0002). Associations with ADEH were stronger with the combined null mutations (OR, 10.1; 4.7-22.1; P = 1.99 x 10(-11)). Associations with the R501X mutation were replicated in the African American population; the null mutation was absent among healthy African American subjects, but present among patients with AD (3.2%; P = .035) and common among patients with ADEH (9.4%; P = .0049). However, the 2282del4 mutation was absent among African American patients with ADEH and rare (<1%) among healthy individuals. CONCLUSION: The R501X mutation in the gene encoding filaggrin, one of the strongest genetic predictors of AD, confers an even greater risk for ADEH in both European and African ancestry populations, suggesting a role for defective skin barrier in this devastating condition.

Relationship between Kaposi's varicelliform eruption in Japanese patients with atopic dermatitis treated with tacrolimus ointment and genetic polymorphisms in the IL-18 gene promoter region.

Kaposi's varicelliform eruption is the most important problem in treating patients with atopic dermatitis (AD) with tacrolimus ointment. It has been considered that Kaposi's varicelliform eruption occurs due to decreased levels of interleukin (IL)-18. The aim of this study was to examine the relationship between Kaposi's varicelliform eruption and genetic polymorphisms in the IL-18 gene. IL-18 gene promoter polymorphisms were analyzed in 21 AD patients treated with tacrolimus ointment and in 100 healthy volunteers. Six AD patients with Kaposi's varicelliform eruption during the treatment with tacrolimus ointment showed significantly higher frequency in G-to-C mutations at the IL-18 gene promoter region -137 compared with 15 AD patients without Kaposi's varicelliform eruption. The 15 AD patients without Kaposi's varicelliform eruption as well as 100 healthy volunteers did not have mutations of G-to-C at the IL-18 gene promoter region -137. These results suggest that the onset of Kaposi's varicelliform eruption following the treatment with tacrolimus ointment is associated with the mutation of G-to-C in the IL-18 gene promoter region -137, and that caution is required when using tacrolimus ointment for treating AD patients with this mutation.

Skin inflammation in RelB(-/-) mice leads to defective immunity and impaired clearance of vaccinia virus.

BACKGROUND: Atopic dermatitis (AD) is an inflammatory skin disorder occurring in genetically predisposed individuals with a systemic T(H)2 bias. Atopic dermatitis patients exposed to the smallpox vaccine, vaccinia virus (VV), occasionally develop eczema vaccinatum (EV), an overwhelming and potentially lethal systemic infection with VV. OBJECTIVE: To establish a murine model of EV and examine the effects of skin inflammation on VV immunity. METHODS: The skin of RelB(-/-) mice, like that of chronic AD lesions in humans, exhibits thickening, eosinophilic infiltration, hyperkeratosis, and acanthosis. RelB(-/-) and wild-type (WT) control mice were infected with VV via skin scarification. Viral spread, cytokine levels, IgG2a responses and VV-specific T cells were measured. RESULTS: Cutaneously VV-infected RelB(-/-), but not WT mice, exhibited weight loss, markedly impaired systemic clearance of the virus and increased contiguous propagation from the inoculation site. This was associated with a dramatically impaired generation of IFN-gamma-producing CD8(+) vaccinia-specific T cells along with decreased secretion of IFN-gamma by VV-stimulated splenocytes. The T(H)2 cytokines-IL-4, IL-5, IL-13, and IL-10-on the other hand, were overproduced. When infected intraperitoneally, RelB(-/-) mice generated robust T cell responses with good IFN-gamma production. CONCLUSION: Allergic inflammation in RelB(-/-) mice is associated with dysregulated immunity to VV encountered via the skin. We speculate that susceptibility of AD patients to overwhelming vaccinia virus infection is similarly related to ineffective T cell responses. CLINICAL IMPLICATIONS: The susceptibility of patients with AD to EV following cutaneous contact with VV is related to ineffective antiviral immune responses.

Selective killing of vaccinia virus by LL-37: implications for eczema vaccinatum.

Possible bioterrorism with smallpox has led to the resumption of smallpox (vaccinia virus) immunization. One complication, eczema vaccinatum, occurs primarily in patients with atopic dermatitis (AD). Skin lesions of patients with AD, but not psoriasis, is deficient in the cathelicidin antimicrobial peptide (LL-37) and human beta-defensin-2 (HBD-2). We hypothesized that this defect may explain the susceptibility of patients with AD to eczema vaccinatum. The Wyeth vaccine strain of vaccinia virus was incubated with varying concentrations of human (LL-37) and murine (CRAMP) cathelicidins, human alpha-defensin (HBD-1, HBD-2), and a control peptide. Outcomes included quantification of viral PFU, vaccinia viral gene expression by quantitative real-time RT-PCR, and changes in virion structure by transmission electron microscopy. CRAMP knockout mice and control animals were inoculated by skin pricks with 2 x 10(5) PFU of vaccinia and examined daily for pox development. Physiologic amounts of human and murine cathelicidins (10-50 micro M), but not human defensins, which had antibacterial activity, resulted in the in vitro reduction of vaccinia viral plaque formation (p < 0.0001), vaccinia mRNA expression (p < 0.001), and alteration of vaccinia virion structure. In vivo vaccinia pox formation occurred in four of six CRAMP knockout animals and in only one of 15 control mice (p < 0.01). These data support a role for cathelicidins in the inhibition of orthopox virus (vaccinia) replication both in vitro and in vivo. Susceptibility of patients with AD to eczema vaccinatum may be due to a deficiency of cathelicidin.