Host biomarkers of clinical relevance in tuberculosis: review of gene and protein expression studies.

CONTEXT: Identification of clinically relevant biomarkers is required for better diagnosis, prevention and treatment of tuberculosis. OBJECTIVE: In this review, potential host biomarkers in blood or blood cells in tuberculosis were identified by a systematic approach. METHODS: A total of 55 articles were selected from PubMed and Google Scholar that analyzed gene and or protein expression in humans in active and or latent TB. Articles were scored according to certain criteria and categorized as strong or weak studies. Biomarkers reported by more than one article or by a single strong article were identified as potential biomarkers. RESULTS: Six most promising markers (IP-10, IL-6, IL-10, IL-4, FOXP3 and IL-12) were identified based on their presence in both mycobacterial antigen-stimulated and -unstimulated samples. CONCLUSIONS: With this review we hope to provide a reliable guideline for biomarker studies in tuberculosis.

Host transcriptional responses following ex vivo re-challenge with Mycobacterium tuberculosis vary with disease status.

The identification of immune correlates that are predictive of disease outcome for tuberculosis remains an ongoing challenge. To address this issue, we evaluated gene expression profiles from peripheral blood mononuclear cells following ex vivo challenge with Mycobacterium tuberculosis, among participants with active TB disease (ATBD, n = 10), latent TB infection (LTBI, n = 10), and previous active TB disease (after successful treatment; PTBD, n = 10), relative to controls (n = 10). Differential gene expression profiles were assessed by suppression-subtractive hybridization, dot blot, real-time polymerase chain reaction, and the comparative cycle threshold methods. Comparing ATBD to control samples, greater fold-increases of gene expression were observed for a number of chemotactic factors (CXCL1, CXCL3, IL8, MCP1, MIP1α). ATBD was also associated with higher IL1B gene expression, relative to controls. Among LTBI samples, gene expression of several chemotactic factors (CXCL2, CXCL3, IL8) was similarly elevated, compared to individuals with PTBD. Our results demonstrated that samples from participants with ATBD and LTBI have distinct gene expression profiles in response to ex vivo M. tuberculosis infection. These findings indicate the value in further characterizing the peripheral responses to M. tuberculosis challenge as a route to defining immune correlates of disease status or outcome.

Analysis of bacteria-challenged wild silkmoth, Antheraea mylitta (lepidoptera) transcriptome reveals potential immune genes.

BACKGROUND: In the recent years a strong resemblance has been observed between the insect immune system and the mammalian innate immune mechanisms suggesting their common origin. Among the insects, only the dipterans (Drosophila and various mosquito species) have been widely investigated for their immune responses towards diverse pathogens. In the present study we constructed and analysed the immune transcriptome of the lepidopteran Antheraea mylitta, an economically important Indian tasar silkmoth with a view to unravel the potential immune-related genes and pathways. RESULTS: An expressed sequence tag (EST) library was constructed from mRNA obtained from fat bodies of A. mylitta larvae that had been challenged by infection with Escherichia coli cells. We identified 719 unique ESTs from a total of 1412 sequences so generated. A third of the transcriptome showed similarity with previously characterized immune-related genes that included both the known and putative immune genes. Of the four putative novel defence proteins (DFPs) annotated by PSI-BLAST three showed similarity to extracellular matrix proteins from vertebrates implicated in innate immunity, while the fourth was similar to, yet distinct from, the anti-microbial protein cecropin. Finally, we analysed the expression profiles of 15 potential immune-related genes, and the majority of them were induced more prominently with E. coli compared to Micrococcus luteus. We also identified several unknown proteins, some of which could have probable immune-related functions based on the results of the ProDom analysis. CONCLUSION: The present study has identified many potential immune-related genes in A. mylitta some of which are vertebrate homologues and others are hitherto unreported putative defence proteins. Several genes were present as members of gene families, as has also been observed in other insect species.

Noduler, a novel immune up-regulated protein mediates nodulation response in insects.

Insect immune system comprises of both humoral and cellular defenses. Nodulation is one of the major, yet very poorly understood cellular responses against microbial infections in insects. Through screening for novel immune genes from an Indian saturniid silkmoth Antheraea mylitta, we identified a protein up-regulated in hemolymph within minutes upon bacterial challenge. We have shown here, for first time, the involvement of this novel protein in mediating nodulation response against bacteria and hence designated it as Noduler. Noduler possessed a characteristic reeler domain found in several extracellular matrix vertebrate proteins. Noduler was shown in vitro to bind a wide range of bacteria, yeast, and also insect hemocytes. Furthermore, Noduler specifically bound LPS, lipotechoic acid, and beta-1, 3 glucan components of microbial cell walls. RNA-interference mediated knock-down of the Noduler resulted in significant reduction in the number of nodules and consequent increase in bacterial load in larval hemolymph. The results suggest that the Noduler is widely conserved and is involved in very early clearance of bacteria by forming nodules of hemocytes and bacterial complexes in insects. The results would promote further studies for understanding of the crucial but hitherto overlooked nodulation mechanism in insects and also provide cues for the study of similar mammalian proteins whose function is not understood.