Innate Immune Responses of Drosophila Melanogaster are Altered by Spaceflight

Alterations and impairment of immune responses in humans present a health risk for space exploration missions. The molecular mechanisms under pinning innate immune defense can be confounded by the complexity of the acquired immune system of humans. Drosophila (fruit fly) innate immunity is simpler, and shares many similarities with human innate immunity at the level of molecular and genetic pathways. The goals of this study were to elucidate fundamental immune processes in Drosophila affected by spaceflight and to measure host-pathogen responses post-flight. Five containers, each containing ten female and five male fruit flies, were housed and bred on the space shuttle (average orbit altitude of330.35 km) for 12 days and 18.5 hours. A new generation of flies was reared in microgravity. In larvae, the immune system was examined by analyzing plasmatocyte number and activity in culture. In adults, the induced immune responses were analyzed by bacterial clearance and quantitative real-time polymerase chain reaction (qPCR) of selected genes following infection with E. coli. The RNA levels of relevant immune pathway genes were determined in both larvae and adults by microarray analysis. The ability of larval plasmatocytes to phagocytose E. coli in culture was attenuated following spaceflight, and in parallel, the expression of genes involved in cell maturation was down regulated. In addition, the level of constitutive expression of pattern recognition receptors and opsonins that specifically recognize bacteria, and of lysozymes, antimicrobial peptide (AMP) pathway and immune stress genes, hallmarks of humoral immunity, were also reduced in larvae. In adults, the efficiency of bacterial clearance measured in vivo following a systemic infection with E. coli post-flight, remained robust. We show that spaceflight altered both cellular and humoral immune responses in Drosophila and that the disruption occurs at multiple interacting pathways

Innate Immune Responses of Drosophila melanogaster Are Altered by Spaceflight

Alterations and impairment of immune responses in humans present a health risk for space exploration missions. The molecular mechanisms underpinning innate immune defense can be confounded by the complexity of the acquired immune system of humans. Drosophila (fruit fly) innate immunity is simpler, and shares many similarities with human innate immunity at the level of molecular and genetic pathways. The goals of this study were to elucidate fundamental immune processes in Drosophila affected by spaceflight and to measure host-pathogen responses post-flight. Five containers, each containing ten female and five male fruit flies, were housed and bred on the space shuttle (average orbit altitude of 330.35 km) for 12 days and 18.5 hours. A new generation of flies was reared in microgravity. In larvae, the immune system was examined by analyzing plasmatocyte number and activity in culture. In adults, the induced immune responses were analyzed by bacterial clearance and quantitative real-time polymerase chain reaction (qPCR) of selected genes following infection with E. coli. The RNA levels of relevant immune pathway genes were determined in both larvae and adults by microarray analysis. The ability of larval plasmatocytes to phagocytose E. coli in culture was attenuated following spaceflight, and in parallel, the expression of genes involved in cell maturation was downregulated. In addition, the level of constitutive expression of pattern recognition receptors and opsonins that specifically recognize bacteria, and of lysozymes, antimicrobial peptide (AMP) pathway and immune stress genes, hallmarks of humoral immunity, were also reduced in larvae. In adults, the efficiency of bacterial clearance measured in vivo following a systemic infection with E. coli post-flight, remained robust. We show that spaceflight altered both cellular and humoral immune responses in Drosophila and that the disruption occurs at multiple interacting pathways

HilE Interacts with HilD and Negatively Regulates hilA Transcription and Expression of the Salmonella enterica Serovar Typhimurium Invasive Phenotype

The ability of Salmonella enterica serovar Typhimurium to traverse the intestinal mucosa of a host is an important step in its ability to initiate gastrointestinal disease. The majority of the genes required for this invasive characteristic are encoded on Salmonella pathogenicity island 1 (SPI1), and their expression is controlled by the transcriptional activator HilA, a member of the OmpR/ToxR family of proteins. A variety of genes (hilC, hilD, fis, sirA/barA, csrAB, phoB, fadD, envZ/ompR, fliZ, hilE, ams, lon, pag, and hha) have been identified that exert positive or negative effects on hilA expression, although the mechanisms by which these gene products function remain relatively unclear. Recent work indicates that the small DNA-binding protein, Hha, has a significant role in repressing hilA transcription and the invasive phenotype, particularly in response to osmolarity signals. We have characterized the Salmonella-specific gene, hilE, and found that it plays an important regulatory role in hilA transcription and invasion gene expression. Mutation of hilE causes derepression of hilA transcription, and overexpression of hilE superrepresses hilA expression and the invasive phenotype. Bacterial two-hybrid experiments indicate that the HilE protein interacts with HilD, suggesting a possible mechanism for HilE negative regulation of hilA gene expression and the Salmonella invasive phenotype. Finally, we have found that the hilE gene resides on a region of the serovar Typhimurium chromosome that has many characteristics of a pathogenicity island

Humoral responses are downregulated in spaceflight larvae.

<p>Gene Ontology (GO) categories of defense response show altered gene expression in flight larvae compared to ground-reared larvae: 30 out of the 37 classified as defense response are downregulated in flight. These include the majority of response to bacteria and in particular humoral response genes. Six experimental repeats of each of the samples (flight and ground) were used to extract RNA for microarray analysis and are represented in individual columns in the figure. Rows represent levels of individual gene expression in each of the experimental repeats. Data is shown following Z-score transformation. Red colors indicate Z-scores >0 (above mean), blue colors indicate Z-scores <0 (below mean). The gene names can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0015361#pone-0015361-t001" target="_blank">Tables 1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0015361#pone-0015361-t002" target="_blank">2</a>.</p

The expression of genes involved in hemocyte maturation and pathogen recognition and binding is downregulated in spaceflight larvae.

<p>Among the major categories of genes that were affected in larvae that developed in microgravity were the genes that mark the differentiation and maturation of plasmatocytes (l(3)mbn, Pxn, Pvf2,) and crystal cells (lz); genes involved in <i>E. coli</i> binding and phagocytosis; and the pattern recognition receptors GNBP3 and PGRPs which activate the humoral pathways. Gene expression level in spaceflight samples compared to ground controls is expressed as fold change. The statistical significance of the gene changes is shown by the adjusted <i>p</i>-value. The false discovery rate (FDR) cut-off was less than 0.05 for all genes.</p

Spaceflight alters phagocytosis.

<p>A. The number of actively phagocytosing cells is reduced by spaceflight. At 15, 25, and 35 minutes, a significantly lower number of cells engulfed <i>E. coli</i> in hemocyte cultures from spaceflight larvae. The calculated <i>p</i>-values were 0.32, 2.16E-07, 3.38E-05, 3.86E-08, and 5.8E-04 for the 5, 15, 25, 35 and 45-minute time points respectively. The data points are tight and give calculated standard error values in the 10⁻² range, not visible on the graph. B. The phagocytic capacity of larval plasmatocytes is stunted. The number of Alexa594-labeled <i>E. coli</i> engulfed by larval plasmatocytes in culture was compared in samples from flight and ground up to 45 minutes after infection. Cells from both space- and ground-reared larvae had similar levels of activity up to 25 minutes post-infection, while after 35 minutes space larvae plasmatocytes had significantly reduced phagocytic capacity.</p

The constitutive expression of humoral immunity genes is altered in spaceflight larvae.

<p>Specific classes of genes involved in the humoral immune response that were altered by spaceflight included: the AMP response pathway, the stress factors turandot A and C, the lysozyme genes and the melanization gene black cells. Although some of the genes upstream of AMPs were upregulated, the target AMP effectors were all downregulated. The statistical significance of gene changes is shown by the adjusted <i>p</i>-value at an FDR threshold of less than 0.05.</p

The ability to clear bacterial infections is maintained in adult flies after spaceflight.

<p>Adults were infected with <i>E. coli</i> HB101 immediately after return from spaceflight. The overall capacity to clear the bacterial infection was measured by quantifying the live bacteria (CFU) remaining in the animal up to 3 days following infection. Flight adults cleared bacteria as effectively as controls immediately after flight, and more efficiently at days 2 and 3 post infection (<i>p-</i>value <0.05).</p