Exosomal-derived miR4485-3p suppresses CD40L to attenuate the function of CD4 + T cells in Mycobacterium leprae infection

Background The expressions of serum exosomes microRNAs (miRNAs) exhibited variations among patients with leprosy, which may have implications for disease diagnosis and treatment. Various miRNAs play crucial roles in the pathogenesis of leprosy infection. Methods We identified miRNAs in three groups of serum exosomes by miRNA microarray. And we expanded up to 30 samples of three groups to validate the differentially expressed miRNAs from serum exosome samples. An human mononuclear/macrophage and Mycobacterium leprae (M. leprae) co-culture system was established in vitro to confirm the expressions of significantly differentially expressed miRNA in supernatant exosomes and cells. Finally, validate the regulatory effects of differentially expressed miRNAs on their predicted target genes through in vitro cell experiments. Results Consequently, we isolated exosomes from the serum samples. The expression of serum exosome miR4485-3p was significantly higher in leprosy patients compared with normal controls (p < 0.01), and both were found to be elevated in multi-bacillary (MB) leprosy patients compared to pauci-bacillary (PB) leprosy patients. After conducting validation experiments, miR-4485-3p was found to be able to distinguish between healthy control individuals and leprosy patients with a sensitivity of 70% and specificity of 73.3%. After transfecting miR4485-3p mimics into monocytes/macrophages treated with Mycobacterium leprae and co-cultivating them with autologous T cells, we observed that it suppressed the function of CD4 ⁺ T cells by down-regulating CD40L expression. Additionally, it also inhibited macrophage activity by down-regulating CD40 expression and decreasing the levels of TNF-α, IL-1β, and IL-6 in the supernatant, thereby promoting bacterial survival. Conclusions We have identified higher expression of miR4485-3p in serum exosomes from leprosy patients. Furthermore, Mycobacterium leprae-infected macrophages can modulate CD40L receptors on the surface of CD4 ⁺ T cells by delivering miR4485-3p via exosomes, thereby impairing their function in the immune response to Mycobacterium leprae infection.