Ge et al. BMC Genomics 2010, 11:456 http://www.biomedcentral.com/1471-2164/11/456 R E S E A R C H A R T I C L E Open Access Microarray Analysis of Response of Salmonella during Infection of HLA-B27- Transfected Human Macrophage-Like U937 Cells Shichao Ge1, Vittoria Danino2, Qiushui He1, Jay CD Hinton2, Kaisa Granfors1* Abstract Background: Human leukocyte antigen (HLA)-B27 is strongly associated with the development of reactive arthritis (ReA) in humans after salmonellosis. Human monocytic U937 cells transfected with HLA-B27 are less able to eliminate intracellular Salmonella enterica serovar Enteritidis than those transfected with control HLA antigens (e.g. HLA-A2). To investigate further the mechanisms by which HLA-B27-transfected cells allow increased replication of these bacteria, a DNA-based microarray was used for comparative genomic analysis of S. Enteritidis grown in HLA-B27- or HLA-A2-transfected cells. The microarray consisted of 5080 oligonucleotides from different serovars of Salmonella including S. Enteritidis PT4-specific genes. Bacterial RNA was isolated from the infected HLA-B27- or HLA-A2-transfected cells, reverse-transcribed to cDNA, and hybridized with the oligonucleotides on the microarrays. Some microarray results were confirmed by RT-PCR. Results: When gene expression was compared between Salmonella grown in HLA-B27 cells and in HLA-A2 cells, 118 of the 4610 S. Enteritidis-related genes differed in expression at 8 h after infection, but no significant difference was detectable at 2 h after infection. These differentially expressed genes are mainly involved in Salmonella virulence, DNA replication, energy conversion and metabolism, and uptake and metabolism of nutrient substances, etc. The difference suggests HLA-B27-dependent modulation of Salmonella gene expression, resulting in increased Salmonella replication in HLA-B27-positive cells. Among the up-regulated genes were those located in Salmonella pathogenicity island (SPI)-2, which play a central role in intracellular survival and replication of Salmonella. Conclusions: This is the first report to show the regulation of Salmonella gene expression by HLA-B27 during infection of host cells. This regulation probably leads to increased Salmonella survival and replication in HLA-B27- positive cells. SPI-2 genes seem to contribute significantly to the increased replication. Background The clinical outcomes of non-typhoidal salmonellosis range from self-limiting gastroenteritis to life-threaten- ing systemic infections [1]. Many serovars of Salmonella enterica cause these infections, serovar Enteritidis being among the most common [2,3]. The acute gastrointest- inal infection caused by Salmonella may result in com- plications such as reactive arthritis (ReA) [4-6]. Originally, ReA was described as an aseptic inflamma- tion that develops after an infection elsewhere in the body [7]. ReA is an asymmetric polyarthritis and the * Correspondence: kaisa.granfors@utu.fi 1Department of Infectious Disease Surveillance and Control, National Institute for Health and Welfare, Turku, Finland Full list of author information is available at the end of the article outcome of the disease ranges from mild symptoms to severe and chronic clinical manifestations. Up to 80% of patients with ReA express the HLA-B27 antigen [8,9]. Macrophages are important in the pathogenesis of Salmonella infections. They are an integral part of the immune response as they present antigens to the innate defence system and communicate with the adaptive immune system to resist the bacterial infection [10-12]. However, unlike many other pathogens, Salmonella can survive inside macrophages by adapting to this particu- lar intracellular environmental niche. After Salmonella uptake into macrophages, the intracellular bacteria reside in large membrane-bound phagosomes, called spacious phagosomes (SP), which develop into Salmo- nella-containing vacuoles (SCV) [13]. The formation of © 2010 Ge et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.