Volume 5 Supplement 4
Analysis of global transcriptional responses of chicken following primary and secondary Eimeria acervulina infections
© Kim et al; licensee BioMed Central Ltd. 2011
Published: 3 June 2011
Characterization of host transcriptional responses during coccidia infections can provide new clues for the development of alternative disease control strategies against these complex protozoan pathogens.
In the current study, we compared chicken duodenal transcriptome profiles following primary and secondary infections with Eimeria acervulina using a 9.6K avian intestinal intraepithelial lymphocyte cDNA microarray (AVIELA).
Gene Ontology analysis showed that primary infection significantly modulated the levels of mRNAs for genes involved in the metabolism of lipids and carbohydrates as well as those for innate immune-related genes. By contrast, secondary infection increased the levels of transcripts encoded by genes related to humoral immunity and reduced the levels of transcripts for the innate immune-related genes. The observed modulation in transcript levels for gene related to energy metabolism and immunity occurred concurrent with the clinical signs of coccidiosis.
Our results suggest that altered expression of a specific set of host genes induced by Eimeria infection may be responsible, in part, for the observed reduction in body weight gain and inflammatory gut damage that characterizes avian coccidiosis.
The apicomplexan E.acervulina specifically infects the duodenum resulting in diarrhea, poor feed conversion, and reduced body weight gain, thereby incurring large economic losses to the poultry industry . Traditional disease control methods have relied on chemoprophylaxis with anti-coccidia drugs or immunization with live/attenuated parasite vaccines . However, novel strategies are sought due to increasing governmental restrictions on the commercial use of coccidiostats, the emergence of drug resistant parasites, and the high costs of new drug/vaccine development. Recent high throughput DNA microarray technology on a whole-genome or tissue-specific basis enables the investigation of complex transcriptional patterns, providing new insights to analyze intricate biological systems, such as host-parasite interactions during coccidiosis . Recently, we constructed a 9.6K intestinal IEL cDNA microarray (AVIELA) which was utilized to show that immune-related genes such as apoptosis as well as the JAK/STAT and MAPK signaling pathways were up- or down-regulated in the jejunum during E. maxima infection . The current study was undertaken using the improved second-generation AVIELA to study local immune responses in chickens infected with a duodenum-infecting coccidia species, E. acervulina, since its host immune response is less known compared to other Eimeria parasites.
Animals, parasites, and experimental infections
Fertilized eggs of White Leghorn chickens (Charles River SPAFAS Laboratories) were hatched at the Animal and Natural Resources Institute (Beltsville, MD). E. acervulina oocysts were cleaned by flotation on 5.25% sodium hypochlorite and washed 3 times with sterile PBS . Chickens were orally inoculated with 1.0 X 104 sporulated oocysts of E. acervulina at 3 weeks of age. Secondary infection with 2.0 X 104 oocysts was given at day 21 post primary infection (i.e. 6 weeks of age). Non-infected 3 week-old and 6 week-old chickens were used as primary and secondary negative controls, respectively. All experiments were approved by the Institutional Animal Care and Use Committee (IACUC) at Animal and Natural Resources Institute.
Isolation of intestinal mucosal tissues, RNA preparation, microarray hybridization, and data analyses
Construction of the AVIELA microarray and isolation of intestinal mucosal tissues were previously described [4, 6]. Intestinal duodenal tissues were removed from 12 chickens/group at daily intervals between days 0 and 8 post-primary or post-secondary infections. The scrapings of mucosal layers from 12 chickens from each group were pooled and total RNA was prepared using TRIzol (Invitrogen) and the RNeasy Mini RNA Purification Kit (Qiagen). The pooled total RNA was used for microarray hybridization and quantitative RT-PCR. DNase-treated total RNA (3.0 μg) from 2 consecutive days were pooled (days 1-2, 3-4, 5-6, and 7-8) and used for synthesis of aminoallyl-labeled RNA (aRNA) using the Amino Allyl Message Amp II aRNA Amplification Kit according to the manufacturer’s protocol (Ambion, Austin, TX). Two 15 μg aliquots of each aRNA were fluorescently labeled with Alexa Fluor 555 or Alexa Fluor 647 (Invitrogen). For hybridization, a circular loop design was employed with technical replication without dye-swap (day 0 vs. days 1-2, days 1-2 vs. 3-4, days 3-4 vs. 5-6, and days 5-6 vs. 7-8) for primary and secondary infections [7, 8]. The microarray data and bioinformatics analyses were performed as previously described . The MIDAS 2.19 of the TM4 package (http://www.tigr.org) was used to qualify and normalize the array data. The poor-quality channel tolerance policy was stringent and the signal-to-noise threshold was 2.0. Two-step normalization, total intensity and global LOWESS (locally-weighted regression and smoothing scatter plots) methods were applied followed by standard deviation (SD) regularization between blocks and slides. The qualified and normalized array data were transferred to GeneSpring GX 7.3 (Silicon Genetics, Redwood, CA) for fold change and statistical analyses. The elements that were modulated ≥ 2.0-fold during primary infection or 1.5-fold during secondary infection were filtered using the Volcano plot to assess statistically significance (p < 0.05). The microarray data and additional information were registered at the NCBI GenBank Gene Expression Omnibus (GEO) repository, series accession number GSE16230.
To confirm gene expression changes observed by microarray analysis, qRT-PCR was performed as previously described  with B2M, CD3D, FBP1, IGJ, IL16, and SOD1 using Mx3000P system and Brilliant SYBR Green QRT-PCR master mix (Stratagene, La Jolla, CA). Standard curves were generated using 2-fold diluted standard RNA and the levels of individual transcripts were normalized to those of GAPDH analyzed by the Q-gene program . To normalize RNA levels between samples within individual experiments, the mean threshold cycle value (Ct) for the target gene and GAPDH products were calculated by pooling values from all samples in that experiment. Statistical test of qRT-PCR was performed using Microsoft Excel 2003 and student T-test was used to test for the group differences.
Status of modulated genes during primary and secondary E. acervulinainfections
Gene Ontology analysis of up- and down-regulated genes during E. acervulinainfections
Validation of AVIELA analysis by qRT-PCR
Comparison of microarray with QRT-PCR data
Fold change with pvalue
1.7 ( 0.001)
This study describes the first report of comparing primary and secondary local global transcriptional responses elicited in the duodenal mucosa following E. acervulina infection. The observed gene expression showed overall responses from various different cell types in duodenum intestine, not from specific cell types that resulted from trafficking or turning over during infection. However, our findings indicated that primary infection modulated the levels of transcripts for genes involved in and lipid/carbohydrate metabolism as well as innate and cellular immunity while secondary infection was associated with changes in transcripts for genes of humoral immunity. These results illustrate the utility of the AVIELA microarray for elucidating the differential mechanisms employed by chickens in responding to Eimeria infection at the transcriptome level and, as such, will provide valuable information for further characterization of host protective immunity to avian enteric pathogens. More importantly, the genes identified in this report may represent novel targets for future genetic modification strategies at the organism level to counteract the effects of coccidiosis.
Expression Analysis Systematic Explorer
expressed sequence tag
Hank’s balanced salt solution
false discovery rate.
This work was supported by funds from the National Research Initiative of the USDA Cooperative State Research, Education and Extension Service, grants # 2002-35204-12368 and # 2004-35204-14798.
This article has been published as part of BMC Proceedings Volume 5 Supplement 4, 2011: Proceedings of the International Symposium on Animal Genomics for Animal Health (AGAH 2010). The full contents of the supplement are available online at http://www.biomedcentral.com/1753-6561/5?issue=S4.
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