Influenza A virus (IAV) infections cause ailment in birds and a number of mammalian species including human population worldwide and have inordinate impact on human health and prosperity.
They are the major causative agents of acute viral infections of the respiratory tract which may cause severity from asymptomatic infection to primary viral pneumonia and death. This virus genome consists of 8 fragments of negative-sense single-stranded RNA which encodes for 11 major proteins (1). In the 20th century, three novel strains of influenza virus arose that caused the 1918, 1957, and 1968 pandemics which lead to high mortality rates (2). The main antigenic elements of influenza A viruses are the hem-agglutinin (H) and neuraminidase (N) trans-membrane glycoproteins. On the basis of the antigenicity of these glycoproteins, influenza A viruses are further divided into 16 H (H1 to H16) and 9 N (N1 to N9) subtypes. Currently, H1N1 and H3N2 subtypes are the main isolates circulating in the human population (3, 4). In human, influenza A virus infection promotes the massive release of inflammatory cytokines and chemokines which lead to pulmonary edema, pneumonia, alveolar hemorrhage (5).
MicroRNAs are small non-coding RNAs (~22 nt), which modulate cellular gene expression by interrupting the mRNA translation. Recent findings report that several host cellular microRNAs (cell associated or cell free) are involved in influenza A virus infection and disease progression in humans. For example, miR- 323, miR-491, and miR-654 bind to the PBI gene and inhibit the replication of the H1N1 influenza A virus (6). While miR-155 gets up-regulate during IAV infection and promotes type I interferon (IFN) signaling which results in activation of host antiviral innate immune response in macrophages (7). Since miRNAs are associated in several cellular processes from developmental biology to disease pathology, they are supposed to be potent modulators of a range of biological processes.
Circulating miRNAs have been reported to exhibit typical expression patterns in context to a number of different pathological conditions, including cardiovascular, cerebrovascular, systemic inflammatory diseases, cancer, infectious diseases and metabolic disorders such as type 2diabetes and obesity (8, 9). Thus, this modulation in expression level of different circulating miRNAs due to influenza virus infection can be quantified or detected in circulation by different techniques which proposed them as potential biomarkers for various diseases.