Homolka, S. | Search bioRxiv

bioRxiv2024

C1q in non-immune human serum has a non-redundant complement function towards clinical Mycobacterium tuberculosis complex strains

The Mycobacterium tuberculosis complex (MTBC) includes three human-adapted species: Mycobacterium tuberculosis, Mycobacterium africanum, and Mycobacterium canettii. With their genetic diversity and inherent virulence, these bacteria interact with host factors to influence tuberculosis (TB) transmission and pathogenesis. A critical yet poorly understood aspect of the immune response in TB involves the role of the complement system. Our study aimed to assess the general interaction between the complement system and key clinical MTBC strains representing the principal lineages known to vary in virulence. We found that not only mannose binding lectin (MBL) from the lectin pathway, but also C1q from the classical pathway directly recognize mycobacteria. While MBL generally showed a higher level of binding than C1q, the binding interactions varied across different MTBC strains. We further observed that complement activation products C4b, C3b and the terminal complement complex (TCC) were deposited on the surface of MTBC strains. Inhibition of MBL alone did not substantially alter complement activation, whereas C1q inhibition ceased activation for most strains investigated. Exposure to human serum did not impact the viability or growth of the MTBC strains. In conclusion, both the classical and lectin pathways of complement via C1q and MBL are activated by a broad range of lineages of the MTBC. The classical pathway is the main complement activator in non-immune serum across diverse MTBC lineages, with C1q playing a potentially novel role in the immune response in TB.

immunology↗

bioRxiv2021

Tuberculostearic acid (TSA)-containing phosphatidylinositols as reliable marker to determine Mycobacterium tuberculosis bacterial burden

It is estimated that approximately one-fourth of the world's population is infected with strains of the Mycobacterium tuberculosis complex (MTBC), the causative agents of tuberculosis (TB). In this study, we present rationally developed molecular markers for bacterial burden, which are derived from mycobacterial phospholipids. Using lipidomic approaches, we show that tuberculostearic acid (TSA)-containing phosphatidylinositols (PI) are present in all clinically relevant MTBC lineages investigated. For the major abundant lipid PI 16:0_19:0 (TSA), a detection limit equivalent to 102 colony forming units (CFU) was determined for bacterial cultures and approximately 103 for cell culture systems. We further developed a mass spectrometry based targeted lipid assay, which - in contrast to bacterial quantification on solid medium - can be performed within several hours including sample preparation. Translation of this indirect and culture-free detection approach allowed the determination of pathogen loads in infected murine macrophages, human neutrophils and murine lung tissue. We show that marker lipids inferred from the mycobacterial PIs are increased in peripheral blood mononuclear cells (PBMCs) of TB patients beyond the lipid metabolic background in comparison to healthy controls. In a small cohort of drug-susceptible TB patients elevated levels of these marker molecules were detected at therapy start and declined following successful anti-tuberculosis treatment. The concentration of TSA-containing PIs can be used as correlate for reliable and rapid quantification of Mycobacterium tuberculosis (Mtb) burden in experimental in vitro model systems and may also provide a clinically relevant tool for monitoring TB therapy. One Sentence SummaryTuberculostearic acid containing phosphatidylinositols represent a novel, fast to measure, reliable correlate of Mycobacterium tuberculosis bacterial burden in experimental model systems, which makes a future clinical application conceivable.

biochemistry↗