Aggregated Mycobacterium tuberculosis Enhances the Inflammatory Response

Area of Science:

• Immunology
• Microbiology
• Pathogenesis

Background:

• Mycobacterium tuberculosis (Mtb) bacilli exhibit aggregation behavior.
• Mtb aggregates were previously shown to cause phagocyte death and subsequent bacterial replication.

Purpose of the Study:

• To investigate the transcriptional response of human macrophages to aggregated Mtb versus non-aggregated Mtb.
• To elucidate the role of Mtb aggregation in tuberculosis pathogenesis.

Main Methods:

• Comparative analysis of transcriptional profiles in human monocyte-derived macrophages after infection with aggregated or non-aggregated Mtb.
• Assessment of phagosome acidification and macrophage cell death.
• Observation of Mtb aggregates in patient granulomas.

Main Results:

• Infection with aggregated Mtb induced early upregulation of pro-inflammatory genes and enhanced TNFα signaling via the NFκB pathway compared to non-aggregated Mtb.
• Phagocytosis of Mtb aggregates resulted in decreased phagosome acidification and increased macrophage cell death.
• Heat-killed Mtb aggregates did not induce significant cell death, indicating a role for viable bacilli.

Conclusions:

• Mtb aggregation significantly enhances pro-inflammatory responses and macrophage death, contributing to Mtb pathogenesis.
• Mtb aggregation may facilitate increased bacterial growth, cell necrosis, and transmission, potentially driving active tuberculosis disease.
• Mtb aggregation represents a potential mechanism for disease progression and spread.