Mycobacterium tuberculosis infected human alveolar macrophages have higher Type I IFN responses compared to monocyte-derived macrophages
M Campo1, KA Dill-McFarland1, GJ Peterson1, SJ Skerrett1, TR Hawn1
1Department of Medicine, Univ of Washington, Seattle WA.
Rationale: Alveolar macrophages (AMs) and recruited monocyte-derived macrophages (MDMs) mediate early lung immune responses to Mycobacterium tuberculosis (Mtb) and are poised to determine the subsequent course of infection. Although previous studies documented differences between human AMs and MDMs, few have described cellular functions that regulate critical steps in anti-microbial responses. We hypothesized that Mtb induces unique and essential anti-microbial pathways in human AMs compared to MDMs.
Methods & Results: Using paired human AMs and 5-day MCSF-derived MDMs from 6 healthy volunteers, we infected cells for 6 hours with Mtb H37Rv, isolated RNA, and analyzed transcriptomic profiles with RNASeq. We first examined whether there were cell specific and Mtb-dependent differentially expressed genes by using four pairwise contrasts between the conditions (AM-media, AM-Mtb, MDM-media, MDM-Mtb). We found 261 genes that were Mtb-dependent in AMs compared to MDMs, 20 that were induced in both cell types but in different directions, and 4029 that were Mtb-dependent in MDMs but not AMs (FDR < 0.05). We used hypergeometric enrichment of genes in Broad Hallmark gene sets to characterize the AM-induced Mtb-dependent genes and found that the top two gene sets were Interferon Alpha Response and Interferon Gamma Response, (FDR < 10E-7). Furthermore, with gene set enrichment analysis (GSEA) of Hallmark gene sets, the same two gene sets were the top two AM-induced Mtb-dependent profiles (FGSEA and GAGE FDR < 0.05). In contrast, different gene sets including TNFA Signaling via NF-kB and MTORC1 Signaling, were highly enriched in MDMs (FDR < 0.05). We next examined candidate genes that might explain the increased Type I IFN responses in AMs and found that IFNB1 and three among 13 IFNa family members (IFNA1, IFNA8 and IFNA13) were upregulated in Mtb-infected AMs compared to MDMs (p < 5.1E-3) with minimal to no expression of the remaining IFNAs in either cell type. We then compared expression of DNA cytosolic sensors which are the major regulators of Type I Interferon secretion. CGAS and PYHIN1 had higher baseline expression and CGAS, STING and IFI16 had higher Mtb-induced expression in AMs compared to MDMs (p < 3.2E-2).
Conclusion: We identified Mtb-induced pathways that were upregulated in human AMs compared to MDMs including the Type I IFN response pathway and individual Type I IFN and DNA sensor genes. Further studies are underway to understand how the Type I IFN interferon pathway is differentially regulated in AMs vs MDMs.