Intact Pneumococci Trigger Transcription of Interferon-Related Genes in Human Monocytes, while Fragmented, Autolyzed Bacteria Subvert This Response

Abstract

A peculiar trait of pneumococci (Streptococcus pneumoniae) is their propensity to undergo spontaneous lysis during stationary growth due to activation of the enzyme autolysin (LytA), which fragments the peptidoglycan cell wall. The fragments that are generated upon autolysis impair phagocytosis and reduce production of interleukin-12 (IL-12) and gamma interferon (IFN-␥) by human leukocytes in response to intact pneumococci, thereby impeding crucial host defenses. The objective was to identify additional monocyte genes whose transcription is induced by intact pneumococci and subverted by autolyzed bacteria. Monocytes were isolated from healthy blood donors and stimulated for 3 h with UV-inactivated S. pneumoniae (Rx1PLY Ϫ LytA ϩ strain), which is capable of autolyzing, its LytA Ϫ isogenic autolysindeficient mutant, or a mixture of the two (containing twice the initial bacterial concentration). Gene expression was assessed by Illumina microarray, and selected findings were confirmed by reverse transcription-quantitative real-time PCR (RT-qPCR), enzyme-linked immunosorbent assay (ELISA), and flow cytometry. In all, we identified 121 genes that were upregulated to a significantly higher degree by intact than autolyzed pneumococci. These included IFNB1 and a large set of interferon-induced genes, such as IFIT3, RSAD2, CFCL1, and CXCL10 genes, as well as IL12B and CD40 genes. RT-qPCR revealed that transcription of these genes in response to intact pneumococci diminished when autolyzed pneumococci were admixed and that this pattern was independent of pneumolysin. Thus, transcription of interferon-related genes is triggered by intact pneumococci and subverted by fragments generated by spontaneous bacterial autolysis. We suggest that interferon-related pathways are important for elimination of pneumococci and that autolysis contributes to virulence by extinguishing these pathways. KEYWORDS Streptococcus pneumoniae, autolysins, inflammation, interferons Infection by the pneumococcus (Streptococcus pneumoniae) is a leading cause of death in young children worldwide (1). Pneumococci are one of the major causes of pneumonia, sepsis, and meningitis, as well as less severe localized respiratory infections, such as acute otitis media and sinusitis.The major defense against pneumococcal infection is phagocyte-mediated killing, and the most prominent virulence factor is the thick and hydrophilic pneumococcal capsule, which impedes phagocytosis. Another well-recognized virulence factor is pneumolysin, a cytolysin that incorporates into cholesterol-rich eukaryotic cell membranes. When present in high concentrations, it lyses the host cells (2), while lower

An in vivo atlas of host–pathogen transcriptomes during Streptococcus pneumoniae colonization and disease

“…Since Spn invasion causes cell stress and death, DNA from damaged mitochondria or dying cells would be another potential trigger of the IFN response during invasion. While Skovbjerg et al ( 52 ) observed the up-regulation of IFN-related genes in vitro in human monocytes exposed to intact and autolyzed Spn , they also demonstrated that it was the intact bacteria that were responsible for IFN stimulation, suggesting that exogenous pneumococcal DNA/RNA from autolyzed bacteria may not be the only stimulant to the IFN pathway. A subset of the host IFN-related genes from a different study [identified by pattern B in figure 1 of Skovbjerg et al ( 52 )] were also up-regulated across all infected tissues in our study.…”

The Opp (AmiACDEF) Oligopeptide Transporter Mediates Resistance of Serotype 2 Streptococcus pneumoniae D39 to Killing by Chemokine CXCL10 and Other Antimicrobial Peptides

“…CXCL9, CXCL10, and CXCL11 are inflammatory CXC family chemokines that interact with the chemokine receptor CXCR3 (8,9) and are produced by pharyngeal epithelial cells in response to gamma interferon (IFN-␥) and tumor necrosis factor alpha (TNF-␣) (10). Numerous studies show CXCL10 and CXCL9 to be highly induced in respiratory cells by bacterial pathogens, including the major human respiratory pathogen Streptococcus pneumoniae (11)(12)(13)(14).…”

“…In addition, nisin and other lantibiotics displace lipid II from its functional localization in Gram-positive bacteria, thus blocking cell wall synthesis (28). While some chemokines and AMPs are constitutively expressed at distinct sites in the host (16), many are induced upon bacterial infection (11,14,29).…”

Transcriptome Analysis of Testes and Uterus: Reproductive Dysfunction Induced by Toxoplasma gondii in Mice

“…On the other hand, the tetrapeptide repeat motif of Ifit3 interacts with the N terminus of TBK1 making a bridging protein that connects TBK1 to MAVS on the mitochondria, and is important for protein transport, translational initiation, cell migration and proliferation, antiviral signaling, and virus replication. Recent studies have found that the protection mechanism of Ifit3 for the host is not only against viruses, but is also effective against tumors such as breast cancer [46], and oral squamous cell carcinoma [47], as well as bacteria and parasite infections such as pneumococcus [48], plasmodium [49]. Among the immune proteins induced by Interferon gamma (IFN-γ), Gbps is one of the most abundant proteins.…”