1. Identify genetic determinants of cockroach allergy by integrating genetic and genomic approaches
2. Gene-environment interaction in the genesis of asthma and allergic diseases
1. Identification of genetic determinants conferring the susceptibility to cockroach sensitization among African Americans. Asthma is the most prevalent serious chronic illness of children in the U.S. It is largely accepted that gene-environment interactions are responsible for the development of asthma, and that cockroach allergy is one of the major risk factors for the development of asthma. While there appears to be a rather clear relationship between allergen exposure and allergen sensitization, a dose-response relationship is mostly relevant for “susceptible” individuals, suggesting that cockroach sensitization is not a function of cockroach allergen exposure alone, and genetic susceptibility may be important. Our current study aim is to identify genetic determinants conferring the susceptibility to cockroach sensitization among African Americans, an underserved minority population at higher risk of disease. Several major factors that will contribute to successful outcomes include: (1) focusing on a common and strong risk factor for asthma: cockroach sensitization; (2) focusing on African American population, an underserved minority population at higher risk of disease; (3) taking advantage of the tremendous work that is currently underway in the genetic analyses of two ongoing genome-wide association Studies (GWAS): primary GWAS analysis in the Genomic Research on Asthma in the African Diaspora (GRAAD) and SNP-for-SNP replication in an independent population participating in the Severe Asthma Research Program (SARP), both part of NHLBI-supported STAMPEED program, and finally (4) we have ready accessibility through our ongoing genetic epidemiology studies to additional African American populations, among them, more than 500 African American subjects with information on cockroach exposure levels available for analysis of gene-environment interaction. The studies proposed in this application will ultimately help us to capture a number of causal variants and genes of interest controlling cockroach sensitization.
2. Identification of candidate genes for specific immune responsiveness to cockroach allergen using high-throughput gene expression profiling.To identify genes involved in the underlying mechanism of specific immune responsiveness to cockroach, we have focused on dendritic cells (DCs) to study the effect of cockroach antigen on DC function in the initiation of the immune response, T cell polarization, and gene expression. Our current studies are: (1) To characterize the specific effects of cockroach extract on DC functions in well-characterized atopic subjects with and without cockroach sensitization by evaluating DC maturation, cytokine production and APC function in T cell polarization ex vivo; and (2) To utilize high-throughput gene expression profiling of isolated DCs for prioritization of candidate genes for cockroach sensitization. We believe that, by combining the findings from this study with results from our ongoing GWAS on asthma for which subjects have also been characterized for cockroach sensitization, we will have the potential to generate a reliable list of candidate genes for specific immune responsiveness to cockroach allergen. These candidates will provide the foundation for a future study to further interrogate the role of relevant polymorphisms and risk of cockroach sensitization.
3. Investigation of the mechanism(s) underlying reduced gamma interferon generation in Atopic Dermatitis and Eczema Herpeticum (ADEH) patients. In the NIH/NIAID sponsored ADVN, the gamma IFN (IFN-?) generation was found to be significantly decreased in PBMC from ADEH+ patients, as compared to ADEH- subjects or normal individuals after stimulation with herpes simplex virus (HSV) ex vivo. IFN-? plays critical roles in the innate and acquired immune responses by activating macrophages, enhancing NK cell activation, and promoting T cell differentiation as well as regulating B cell isotope switching to IgG2a. To investigate the mechanism(s) underlying reduced gamma interferon generation in ADEH patients, we are selecting functional SNPs within the coding and regulatory regions of genes related to IFN production (e.g. IFNG, IFNGR1) and genes identified through the genomic study and genome-wide association study (GWAS) of ADEH and are performing association studies in two independent populations, including 449 European American subjects consisting of 292 unrelated AD patients (127 with ADEH) and 157 healthy controls and 366 African American subjects consisting of 202 AD patients (36 with ADEH) and 164 healthy controls. These subjects were originally recruited as a part of the consortium for the Atopic Dermatitis and Vaccinia Network (ADVN). Functional analyses will follow for those genetic variants identified to be associated with disease in order to discover the relevance of these variants to disease.
4. Gene-environment interaction in the genesis of asthma and allergic diseases. Circulating fibrocytes are a distinct population of leukocytes with characteristics of fibroblasts, and are fully functional for the presentation of antigens to naïve T cells. Aryl hydrocarbon receptor (AhR) is a multifunctional regulator that senses and responds to environmental stimuli. Recent studies demonstrated that AhR can mediate an important immune response induced by polycyclic aromatic hydrocarbon (PAH), a major component in airborne particulate matter (APM) that is associated with increased asthma morbidity. Our study will: 1) characterize the effects of cockroach allergen/APM on fibrocyte functions by evaluating cell maturation, cytokine production, and antigen-presenting function in T cell proliferation and differentiation. These studies will test the hypothesis that circulating fibrocytes can respond to cockroach allergen/APM and play a role in the presentation of antigens to naïve T cells and lead to a T cell differentiation (Th1/Th2/Treg/Th17); 2) study the involvement of AhR in cockroach allergen/APM induced immune responses by examining the differential gene expression in the AhR pathway (AhR, ARNT, AHRR, CYP1A1) on fibrocytes in atopic asthma versus healthy control subjects and in the presence and absence of cockroach allergen/APM. AhR agonist/antagonists and AhR knockdown fibrocytes will be used in the studies to test the involvement of AhR.
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- Gao PS, Grigoryev DN, Rafaels NM, Mu DG, Wright JM, et al. CD14, a Key Candidate Gene Associated with Specific Immune Response to Cockroach. Clin Exp Allergy 2010, Jul 4. [Epub ahead of print].
Peisong Gao M.D., Ph.D
Last Updated: 7/31/10