The macrophage is the main replication niche of Mtb, despite the bactericidal characteristics and functions that this cell type normally has. The Mtb has evolved several strategies to reside and even replicate within the otherwise hostile environment of the macrophage, including the prevention of phagosome-lysosome fusion, inhibition of phagosomal maturation, and detoxification of the host’s stresses. Accordingly, the localization of Mtb inside the macrophage has been a matter of debate in recent years
. For a long time, an impermeable phagosome in the macrophage was thought to contain Mtb. However, recent evidence indicates that Mtb, as well as M. leprae, can escape its vacuole and reside in the host cell cytosol
. It is becoming clear that LTBI is not a static state with a homogenous population of non-replicating bacilli, but a constant endogenous Mtb reinfection process
. It is argued that both phagosomal maturation inhibition and escape from the phagosome are part of the survival strategies of Mtb. Owing to the lack of widely accepted animal or in vitro models to reflect the complex biology of LTBI, population-based studies are considered the best methods to investigate the intricate nature of LTBI. In some previous reports, human cell line U937 was used as in vitro model to investigate the molecular mechanism of Mtb during infection or persistence and its effect on the cell
[16, 17]. In this study, U937 cells expressing Hsp16.3 in the cytosol could partialy reflect the dynamic interplay of macrophages with dormant Mtb, which is necessary to prevent reactivation of the bacilli and development of active TB.
Indeed, some miRNAs that have been previously linked to carcinogenesis of different organs and tissues, such as miR-424-5p (previous ID: miR-424), miR-221-5p (previous ID: miR-221*), miR-675, miR-647, miR-125a-5p, miR-214-3p (previous ID: miR-214), miR-130b-3p (previous ID: miR-130b), miR-522-3p (previous ID: miR-522), and miR-16-5p (previous ID: miR-16)
[18–21] were found to be up- or downregulated in our analysis. Forrest and colleagues
 showed that induction of miR-424 (miR-424-5p) and miR-222 (miR-222-3p) promotes monocytic differentiation via combined regulation; both of these miRNAs were significantly downregulated in this analysis. Interestingly, miR-150-5p (previous ID: miR-150) has been shown to regulate the immune response and monocyte differentiation
; miR-150-5p was upregulated in our analysis. Conversely, miR-181a (miR-181a-5p) and miR-146a (miR-146a-5p), which have been proven to participate in the regulation of the adaptive immune responses, were 7- and 10-fold downregulated in our profiling data
[24, 25]. Furthermore, current research has demonstrated that miR-181a regulates inflammation responses in macrophages, and increased expression of miR-181a is strongly correlated with the expression of interleukin (IL)-1β, IL-6, and tumor necrosis factor alpha (TNFα)
. These results suggest that Hsp16.3 protein might be involved in blocking immunity against Mtb via miR-181a and miR-146a deregulation. In addition, Fu et al. demonstrated that miR-93*(miR-93-3p) was the most upregulated in active TB serum
; however, our analysis indicated that miR-93-3p was downregulated, making it a potential diagnostic marker to distinguish latent TB from active TB.
Although many target genes have been predicted by bioinformatic methods, the functions of most differentially expressed miRNAs remain unknown, and very few predicted target genes have been validated. More than half of the differentially expressed miRNAs did not find a target mRNA in either database; most of them were recently identified miRNAs. Bioinformatic exploratory provides a rapid analytic approach categorizing large amounts of genes into functionally related groups to thereby facilitate the uncovering of the biological content captured by transcriptomic profiling. KEGG pathway enrichment analyses further interpret the biological functions of these genes. The overrepresented pathways associated with glioma and basal cell carcinoma were enriched, which somewhat surprised. The formation of extra-pulmonary tuberculosis is caused by Mtb dissemination to other organs or tissue, such as the central nervous system (CNS)
. It is speculated that the occurrence of glioma might be related to tuberculoma in the CNS, and a tuberculoma-like granuloma is often misdiagnosed as a tumor
. This indicated that Mtb Hsp16.3 might be involved in carcinogenesis, which warrants further investigation.
Earlier studies, which used peripheral blood mononuclear cells (PBMCs) or whole blood cells to perform whole genome transcriptional profiling and miRNA profiling
[27, 30], described a number of candidate biomarkers that might function in active TB. Wang and collegues identified miRNAs that were differently expressed in latent TB versus healthy from the clinical PBMC samples
, In present study, the microarray data and independent qRT-PCR results indicated that our in vitro model by used of U937 cells expressing Mtb Hsp16.3 protein has good repeatability. However, the weakness of the model is also obvious, it does not represent the real interaction of pathogen and host macrophage in vivo, it provided only mechanistic insights on the interaction between Mtb antigen and human cell line. Although the expressions of miR-424-5p (previous ID: miR-424), miR-27a-3p, miR-377-5p and miR-3680-5p were consistent in clinical PBMC samples, the small size of healthy controls weakened the statistical power. Our understanding the biology of latent tuberculosis as part of a broad range of responses that occur following infection with Mtb remains incomplete. Multiple factors are involved in this complex process. Herein, compared to previously studies, our experiments got more differentially expressed miRNAs since we focused on just whether the Mtb Hsp16.3 had great effects on the U937 macrophage cell. Furthermore, this model could also be used in the follow-up investigation of the miRNA candidates regulating the macrophage in chronic inflammatory response or other process correlated with LTBI.