Mycobacterium tuberculosis stimulates IL-1β production by macrophages in an ESAT-6 dependent manner with the involvement of serum amyloid A3

Despite its critical roles in immune responses against tuberculosis infection and immune pathology, the molecular details of interleukin (IL)-1 beta production in tuberculosis infection remain elusive. To explore IL-1 beta production in tuberculosis infection, we infected mouse bone marrow-derived macrophages (BMDM) with Mycobacterium tuberculosis (Mtb) H37Rv, its early secreted antigenic target protein of 6 kDa (ESAT-6) gene deletion (H37Rv:Delta 3875) or complemented strain (H37Rv:Delta 3875C) and evaluated IL-1 beta production. H37Rv induced significantly increased IL-1 beta production by BMDMs compared to non-infected BMDMs. In contrast, H37Rv:Delta 3875 induced significantly less mature IL-1 beta production despite eliciting comparable levels of pro-IL-1 beta and IL-8 from BMDMs compared to H37Rv and H37Rv:Delta 3875C. Blocking either NLRP3 or K+ efflux diminished H37Rv-induced IL-1 beta production by BMDMs. Infection of mice intranasally with H37Rv:Delta 3875 induced less IL1 beta production in the lungs compared with H37Rv. Intranasal delivery of ESAT-6 but not CFP10 induced production of IL-1 beta in mouse lungs and RNA-Seq analysis identified serum amyloid A (SAA) 3 as one of the highly expressed genes in mouse lungs. Infection of mice with H37Rv but not H37Rv:Delta 3875 induced expression of lung SAA3 mRNA and protein, consistent with the effect of intranasal delivery of ESAT-6. Silencing SAA3 reduced Mtb-induced IL-1 beta production by BMDMs. We conclude that SAA3 plays critical role in ESAT-6 dependent IL-1 beta production by macrophages in tuberculosis infection.

Automated summary

The study reveals the critical role of SAA3 in ESAT-6 dependent IL-1β production by macrophages during tuberculosis infection, suggesting its involvement in regulating immune responses by influencing macrophage function.