Immunological and microbial shifts in the aging rhesus macaque lung during nontuberculous mycobacterial infection - 16s

Nontuberculous mycobacteria (NTM) are environmentally ubiquitous organisms that predominately cause pulmonary disease (NTMPD) primarily in those over the age of 65. The incidence of NTMPD has steadily increased in the US, now exceeding that of Mycobacterium tuberculosis (M. tb), making it a disease of high consequence. However, the mechanisms leading to higher susceptibility and severity of NTMPD with aging are poorly defined. Here, we compared host response following inoculation of young and aged rhesus macaque in the right caudal lobe with M. avium subsp. hominissuis (MAH) to address this knowledge gap. Bacterial load, microbial community compositions, and host responses were monitored longitudinally using bacterial culture, immunological assays, 16S amplicon sequencing, and single cell genomics assays. Unilateral infection resulted in comparable, albeit low bacterial load in both young and aged animals that was confined to the infected side. A robust inflammatory response was predominantly in the inoculated lung, however, immune cell infiltration and antigen-specific T-cell responses were detected in both lungs. Computed tomography, gross pathology and histopathology examination revealed increased disease severity in aged versus young animals. Nasal, oral and fecal swabs, and BAL samples showed decompartmentalization of the lower respiratory microbiome and translocation of bacterial DNA typically found in the gut and oral-pharyngeal cavity. Finally, single-cell RNA sequencing indicated that aged animals generated a heightened inflammatory response to MAH infection. Collectively these data suggest that increased disease severity in the aged is mediated by a dysregulated macrophage response rather than higher bacterial burden.