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The phenotypical consequences of a combined deficiency of the Fas-Fas Ligand (FasL) and one or both Tumor Necrosis Factor (TNF) signaling pathways were investigated. Mice, which expressed a non-functional FasL suffered from a pathological accumulation of both B and T cells leading to splenomegaly and lymphadenopathy and, depending on the genetic background, pathogenic self-reactive antibodies (generalized lymphoproliferative disorder (gld)-phenotype). If mice additionally lacked TNF, they displayed a significantly ameliorated gld-phenotype while TNF Receptor-1-deficient gld mice (B6.gld.TNFR1−/−) displayed a more severe phenotype. To complement this combination, we also generated TNF Receptor-2-deficient gld mice (B6.gld.TNFR2−/−). Both double knockouts followed in their splenic structure the respective TNFR contribution to the phenotype. TNFR1−/− mice showed an absence of B cell follicles in the spleen while TNFR2−/− mice were comparable to WT mice. In general, we demonstrated a strong contribution of both TNFR signaling pathways to the symptoms of gld with the notable exception of splenomegaly where only TNFR1−/− played a role.

Colistin (polymyxin E) is a membrane-destabilizing antibiotic used against Gram-negative bacteria. We have recently reported that the outer membrane prevents the uptake of antibacterial chlorophyllin into Gram-negative cells. In this study, we used sub-toxic concentrations of colistin to weaken this barrier for a combination treatment of Escherichia coli and Salmonella enterica serovar Typhimurium with chlorophyllin. In the presence of 0.25 µg/mL colistin, chlorophyllin was able to inactivate both bacteria strains at concentrations of 5−10 mg/L for E. coli and 0.5−1 mg/L for S. Typhimurium, which showed a higher overall susceptibility to chlorophyllin treatment. In accordance with a previous study, chlorophyllin has proven antibacterial activity both as a photosensitizer, illuminated with 12 mW/cm2, and in darkness. Our data clearly confirmed the relevance of the outer membrane in protection against xenobiotics. Combination treatment with colistin broadens chlorophyllin’s application spectrum against Gram-negatives and gives rise to the assumption that chlorophyllin together with cell membrane-destabilizing substances may become a promising approach in bacteria control. Furthermore, we demonstrated that colistin acts as a door opener even for the photodynamic inactivation of colistin-resistant (mcr-1-positive) E. coli cells by chlorophyllin, which could help us to overcome this antimicrobial resistance.