Linda A. Fischbacher

Abstract Pulmonary tuberculosis (TB) exhibits marked spatial heterogeneity, with alveolar pneumonia and organized granulomas frequently coexisting within the same lung. While granulomas have long dominated conceptual models of TB pathogenesis, the immune programs operating within alveolar TB pneumonia in humans remain incompletely defined. Here, we integrate spatial transcriptomics, single-cell RNA sequencing, high-resolution imaging, and functional assays of human lung biopsies to directly compare alveolar pneumonia with adjacent granulomas from the same individuals. We demonstrate that alveolar TB pneumonia is enriched for TREM2⁺ lipid-laden macrophages characterized by lipid metabolic reprogramming, sparse T-cell infiltration, attenuated antimicrobial gene expression, and abundant Mycobacterium tuberculosis ( Mtb ) transcripts and antigens. In contrast, neighboring granulomas exhibit organized lymphoid architecture and robust antimicrobial programs. Mechanistically, the mycobacterial virulence lipid phthiocerol dimycocerosate (PDIM) and free mycolic acids induce TREM2 expression and activate TREM2–DAP12 signaling, promoting lipid droplet accumulation, suppressing autophagy, and enhancing intracellular Mtb survival in human macrophages. This immunometabolic state is pharmacologically reversible: 1,25-dihydroxyvitamin D₃ downregulates TREM2, restores autophagy, reduces lipid droplets, and limits bacterial viability. Together, these findings define a spatially localized TREM2⁺ foamy macrophage program within alveolar pneumonia that contrasts sharply with adjacent granulomatous immunity, establishing an niche permissive for bacillary persistence and potentially transmission, as well as identifying a tractable host pathway in human TB pathogenesis.

Hintergrund und Zielsetzung: Die steigende Prävalenz von Typ 2 Diabetes mellitus (T2D) weltweit erfordert effektive Therapieansätze, um Folgeerkrankungen zu verhindern. Diese Bachelorarbeit untersucht die Auswirkungen der ketogenen Ernährung (KD) auf den HbA1c-Wert sowie ausgewählte Lipidstoffwechselparameter bei Patienten mit T2D. Ziel ist es, das therapeutische Potential der KD hinsichtlich der Senkung von HbA1c und Triglyceriden sowie der Beeinflussung von LDL- und HDL-Cholesterin zu analysieren und zu diskutieren. Methode: Zur Beantwortung der Forschungsfragen wurden eine Literaturrecherche und qualitative Experteninterviews durchgeführt. Die Recherche umfasste Leitlinien verschiedener Fachgesellschaften, Studien aus PubMed und Fachbücher. Die Interviews lieferten vertiefte Einblicke in die praktische Anwendung und Wirksamkeit der KD bei Personen mit T2D. Ergebnisse: Die Ergebnisse zeigen, dass die KD kurzfristig zu einer signifikanten Senkung des HbA1c und der Triglyceride führt, trotz Reduktion der antidiabetischen Medikation. Zudem erhöht die KD meist das HDL, während das LDL ansteigen kann. Jedoch verringern sich die gefährlichen atherogenen Small-Density-LDL-Unterfraktionen. Die KD führt zur Verbesserung der glykämischen Kontrolle und zur Reduktion der Insulinresistenz. Langfristig kann die KD bzw. Low Carb Ernährung bei einigen Patienten sogar zu einer Remission des Diabetes führen. Conclusio: Die KD stellt eine vielversprechende Ernährungsstrategie für Personen mit T2D dar, um den HbA1c und bestimmte Lipidstoffwechselparameter zu verbessern. Trotz der positiven Ergebnisse bleibt die KD kontrovers und erfordert weitere Forschung, um langfristige Effekte und mögliche Risiken besser zu verstehen. Die Ergebnisse dieser Arbeit unterstützen die Integration der KD als Option in die Ernährungstherapie von T2D-Patienten, wobei individualisierte Ansätze und eine enge medizinische Überwachung essenziell sind.

SUMMARY Langerhans cells express the nonpolymorphic antigen-presenting molecule CD1a, positioning them as contributors to host immunity against Mycobacterium leprae in human leprosy. CD1a was originally shown to present non-canonical lipopeptide antigens such as dideoxymycobactin and chemically diverse hydrophobic ligands. Here, we generated CD4⁺ T cell lines from leprosy lesions that recognized M. leprae in a CD1a-restricted manner. Unexpectedly, antigen recognition was protease-sensitive, prompting biochemical purification that identified two microbial protein antigens: LppX, a 25-kDa lipoglycoprotein, and Ag85A, a 30-kDa secreted protein with no known lipid modification. Recombinant proteins activated the corresponding T cell lines in a CD1a-dependent manner. Epitope mapping identified 12-mer peptides that fully reconstituted antigenicity, were conserved between M. leprae and M. tuberculosis , and elicited robust, dose-dependent IFN-γ production and T cell proliferation, establishing that DNA-encoded, ribosomally translated peptides serve as CD1a-restricted cognate antigens. Biochemical analyses showed peptide binding to CD1a, supported by isoelectric focusing and surface plasmon resonance ( K D ∼75 μM for Ag85A). CD1a–peptide tetramers specifically stained cognate T cells, soluble CD1a was sufficient to present peptide antigen, and transfer of the LppX-specific TCR into naïve T cells restored antigen responsiveness. Using CD1a–peptide tetramers, we identified antigen-specific T cells enriched in patients undergoing reversal reactions compared with patients with lepromatous leprosy and healthy donors. The CD1a-restricted T cell lines secreted IFN-γ and IL-26, cytokines with established antimicrobial activity. Together, these findings demonstrate that CD1a can present canonical microbial peptides as part of a cell-mediated immune response in leprosy, extending the known spectrum of CD1a ligands. Because CD1a is nonpolymorphic and presents antigens to antimicrobial T cells, CD1a–peptide complexes may provide a broadly applicable platform for studying, detecting, and potentially targeting mycobacterial immunity.

ABSTRACT Although the current multidrug therapy (MDT) for leprosy is very successful, the long treatment duration and the emergence of antibiotic-resistant strains demand for new alternative drugs. One potential target for drug development against pathogenic mycobacteria is their need to degrade host cholesterol during infection. Mycobacterium leprae , due to its degenerate genome, has preserved only the first step of cholesterol catabolism, in which cholesterol is oxidized to cholestenone by the enzyme 3β-hydroxysteroid dehydrogenase (3β-HSD). M. leprae avidly produces cholestenone in vivo, and this metabolic activity seems to play an important role in bacterial pathogenesis. In this study, six 6-azasteroid analogs were developed with the potential to inhibit 3β-HSD, and their metabolic stability and in vitro and in vivo inhibitory activity against M. leprae were investigated. Pharmacologic properties indicated lower metabolic liabilities for azasteroid 5 in comparison to its progenitors, azasteroids 1 and 2, resulting in improved accumulation and extended t 1/2 values in mice. Azasteroid 5 also partially inhibits M. leprae 3β-HSD in vitro . When tested in the Shepard’s mouse footpad model of leprosy, azasteroid 5 showed effective bacterial killing that was accelerated when combined with a subinhibitory dose of rifampicin and exhibited an absence of detectable hepatotoxic effects. We concluded that 6-azasteroids derivatives are promising new antimicrobial candidates for leprosy treatment. IMPORTANCE Leprosy remains a significant global health challenge, particularly in underserved regions. While multidrug therapy (MDT) has been effective, its prolonged duration and the emergence of antibiotic-resistant strains emphasize the urgent need for novel therapeutic strategies. Recent advances in understanding Mycobacterium leprae ’s unique biology have identified cholesterol metabolism as a critical pathway for bacterial survival and pathogenesis, offering a promising new target for drug development. Building on insights from tuberculosis research, azasteroids—compounds known for their potential to disrupt mycobacterial cholesterol metabolism—are now being explored as candidates for leprosy treatment. These molecules inhibit M. leprae ’s cholesterol oxidation, impairing bacterial persistence within the host. This innovative approach could lead to more effective, faster-acting therapies, overcoming current treatment limitations and resistance. Such efforts represent a vital step forward in reducing the burden of leprosy and empowering affected communities worldwide.