Lipocalin-2 Functions as Inhibitor of Innate Resistance to Mycobacterium tuberculosis

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Lipocalin-2 is an inflammatory protein that typically inhibits bacterial growth by sequestering iron.
• Its role in innate immunity against intracellular bacteria like Mycobacterium tuberculosis (M.tb) is not fully understood.

Purpose of the Study:

• To investigate the specific role of lipocalin-2 in the host immune response to Mycobacterium tuberculosis infection.
• To determine the cellular sources of lipocalin-2 that influence M.tb pathogenesis.

Main Methods:

• Utilized mixed bone marrow chimeras to differentiate the contribution of lipocalin-2 from various cell types.
• Analyzed M.tb infection progression at early (3 weeks) and later (5 weeks) stages post-challenge.
• Examined the co-localization of granulocytes and M.tb within developing granulomas.

Main Results:

• Lipocalin-2 derived from granulocytes, but not macrophages or epithelia, significantly increased susceptibility to M.tb infection in early stages.
• Mycobacterial growth was enhanced by neutrophil-derived lipocalin-2 at 3 weeks post-infection.
• This growth-promoting effect was absent at 5 weeks post-infection, coinciding with granuloma maturation.

Conclusions:

• Neutrophil-derived lipocalin-2 paradoxically supports M.tb growth in early infection, potentially by providing iron within immature granulomas.
• The source of lipocalin-2 is critical in determining its impact on M.tb pathogenesis.
• These findings highlight a complex interplay between host immunity and bacterial adaptation during tuberculosis.