Pathways Activated during Human Asthma Exacerbation as Revealed by Gene Expression Patterns in Blood

Abstract

BackgroundAsthma exacerbations remain a major unmet clinical need. The difficulty in obtaining airway tissue and bronchoalveolar lavage samples during exacerbations has greatly hampered study of naturally occurring exacerbations. This study was conducted to determine if mRNA profiling of peripheral blood mononuclear cells (PBMCs) could provide information on the systemic molecular pathways involved during asthma exacerbations.Methodology/Principal FindingsOver the course of one year, gene expression levels during stable asthma, exacerbation, and two weeks after an exacerbation were compared using oligonucleotide arrays. For each of 118 subjects who experienced at least one asthma exacerbation, the gene expression patterns in a sample of peripheral blood mononuclear cells collected during an exacerbation episode were compared to patterns observed in multiple samples from the same subject collected during quiescent asthma. Analysis of covariance identified genes whose levels of expression changed during exacerbations and returned to quiescent levels by two weeks. Heterogeneity among visits in expression profiles was examined using K-means clustering. Three distinct exacerbation-associated gene expression signatures were identified. One signature indicated that, even among patients without symptoms of respiratory infection, genes of innate immunity were activated. Antigen-independent T cell activation mediated by IL15 was also indicated by this signature. A second signature revealed strong evidence of lymphocyte activation through antigen receptors and subsequent downstream events of adaptive immunity. The number of genes identified in the third signature was too few to draw conclusions on the mechanisms driving those exacerbations.Conclusions/SignificanceThis study has shown that analysis of PBMCs reveals systemic changes accompanying asthma exacerbation and has laid the foundation for future comparative studies using PBMCs.

Gene Expression Profiling in Blood Provides Reproducible Molecular Insights into Asthma Control

“…Three studies of small or modest size have profiled gene expression during acute exacerbation in blood or nasal cells, reporting up-regulation of similar pathways related to innate and adaptive immune responses (3)(4)(5). However, these studies focused on expression changes during acute exacerbations and provided no information regarding expression across the broad range of asthma control states that precede exacerbation.…”

“…Using clinical phenotype data available in Asthma BRIDGE and in CAMP, we developed two composite scores summarizing self-reported asthma control in the preceding 6 months (chronic, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and 7 days (acute, 0-28), respectively, each modeled on the ACT questionnaire (11), where higher scores indicate worse asthma control. Based on the medians of the corresponding phenotypic distributions, optimal chronic asthma control was defined as a score less than or equal to six in BRIDGE WB and moderately suboptimal asthma control was defined as a score less than or equal to 11 in BRIDGE CD4 ( Figure 2).…”

A Nonmuscle Myosin Light Chain Kinase–Dependent Gene Signature in Peripheral Blood Mononuclear Cells is Linked to Human Asthma Severity and Exacerbation Status

“…8 Therefore, with these control comparators for samples obtained from the same patient, we applied ANCOVA to compare gene expression between stable and exacerbation status. We identified 1,245 genes differentially expressed between stable and asthma exacerbation status (Table S4), with 52 genes overlapping with nmMLCK-influenced genes (P = 3.7 × 10 −2 by cumulative hypergeometric distribution function).…”

Exacerbating Factors Induce Different Gene Expression Profiles in Peripheral Blood Mononuclear Cells from Asthmatics, Patients with Chronic Obstructive Pulmonary Disease and Healthy Subjects

“…We employed PBMC to study allergen-/LPS-specific responses. They are easily accessible and widely used in in vitro studies, which is in contrast to airway tissue or lavage samples [71]. However, it has been noted that technical aspects of blood sampling, isolation of PBMC, RNA isolation techniques and time to analysis and temperature during blood processing may affect gene expression patterns [72,73].…”