The use of novel lung alveolar macrophage model, Max Planck Institute cells, to demonstrate the differential effects of smooth and rough mycobacterium abscessus forms on IL-6 and IL-1B induction

Abstract

Mycobacterium abscessus frequently initiates respiratory infections in humans and is of clinical concern in patients with cystic fibrosis who develop secondary pulmonary infections. Alveolar macrophages and innate responses play a crucial role in the pathogenesis of M. abscessus. The virulence potential of M. abscessus was suggestive of cell surface transition of glycopeptidolipid loss from the smooth biofilm producing strain to transform into the rough invasive variant. This study focuses on innate responses of three strains of M. abscessus; NCTC rough morphotype, CL-B (DC088-B) smooth morphotype and CL-C (DC088-C) mixed morphotype; each isolated and used as heat and formalin killed stimulants. A novel Max Planck Institute (MPI) macrophage model was used to replicate the alveolar lung macrophage responses, additionally benefiting from self-renewing properties and ease of availability. MPI- macrophages were stimulated and cytokines IL-6 and IL-1β were studied over time periods of 5, 24, 48, 72 and 120 hours. As our primary aim, host inflammatory responses were analysed for variances in the levels of cytokines produced by different strains of M. abscessus and if heat or formalin inactivation had any impact. Bacteria were inactivated to prevent replication but still induce a cytokine response from the macrophages. Previous research concluded rough colony type was more aggressive in potentiating the pathogenic process of M. abscessus. Therefore, we studied variances between the smooth and rough morphotypes. Results indicate rough colony NCTC strain presented overall highest IL-6 levels when the heat-killed, rather than the formalin killed form, was used. Smooth colony type, CL-B strain had consistently low IL-6 levels across both inactivation types. Formalin killed mixed colony type CL-C strain induced higher secretion of IL-6 cytokine compared to formalin killed N-strain and B-strain. IL-1β was poorly induced across all three strains, however the formalin killed bacteria seemed to induce a relatively high IL-1β compared to the heat-killed method with all three strains. CL-C strain relatively displayed the highest IL-1β titres across both inactivation types. In the Max Planck Institute macrophage model, the M. abscessus mixed colony variant induced a larger cytokine response than the rough or the smooth variant. Results obtained from stimulation with MPI-cells potentially benefit personalized therapy towards patients via isolation of the bacteria and modification of treatment depending on the M. abscessus strain.