MicroRNAs (miRNAs) play a critical role in various biological processes through regulation of gene expression post-transcriptionally. Although miRNAs are involved in cell proliferation and differentiation in mammals, few reports regarding the effects of host miRNAs on macrophage activation and differentiation are available in birds. Here, we reported that gga-miR-200b-3p acts as a positive regulator, enhancing macrophage activation and differentiation using an avian model. We found that ectopic expression of gga-miR-200b-3p in HD11 cells enhances the amount of MHC-II-positive cells and promotes the expression of pro-inflammatory cytokines and that gga-miR-200b-3p directly targets monocyte to macrophage differentiation-associated (MMD). The inhibition of MMD by gga-miR-200b-3p enhances the activation and differentiation of HD11 cells and increases the expression of pro-inflammatory cytokines. Collectively, these findings highlight a crucial role of gga-miR-200b-3p in macrophage activation and differentiation in birds.

Background As a major stressor, high temperatures negatively affect the poultry industry, through impairments to chicken immunity and production performance. The purpose of this study is to clarify how chicken immune systems responded to heat stress with and without immunization. In the present study, spleen and bursa of Fabricius of experimental chickens were subjected to RNA-seq. Key genes influencing immune response in heat-stressed chickens were identified and their functions validated. Results Immunized and heat-stressed chickens experienced a significant reduction in immune function. The expression of immune-related genes and heat stress-related genes in the spleen increased after immunization and decreased after heat stress, but in the bursa of Fabricius, few of these genes were differentially expressed after immunization and heat stress, indicating insensitivity to high temperature and the lack of vaccine processing. In the non-heat-stressed groups, spleen expression of DUSP1 and HSPA5 decreased significantly, suggesting their relationship to immunity. Upon DUSP1 or HSPA5 overexpression, the mRNA expression of MHC-I, MHC-II, CD80, CD86, CD1C, IL1B, IL6, and TLR4 was earlier than that under LPS stimulation only, indicating that DUSP1 or HSPA5 overexpression enhances HD11 recognition LPS. Inhibiting DUSP1 or HSPA5 expression, the mRNA expression levels of MHC-I, MHC-II, CD80, CD86, IL6 and TLR4 did not change significantly from LPS-stimulation-only levels but CD1C significantly decreased, suggesting that HD11 recognition of LPS is affected by DUSP1 or HSPA5 expression levels. Conclusions The inhibition of immune response due to lowly expressed DUSP1 and HSPA5 may be the cause of decreased immunity in chickens.