Abstract
Tuberculosis (TB), caused by Mycobacterium tuberculosis, is a serious lung infection leading to over one million deaths annually. Bacille Calmette Guérin (BCG) is the only licensed vaccine for the prevention of TB. It is critical that the immunological basis for protection provided by the BCG vaccine is understood, as new vaccine-resistant strains of M. tuberculosis are becoming more prevalent. The protective mechanisms of BCG are not well understood despite its development over a century ago, although recent evidence has pointed towards trained innate immunity playing an important role. Trained immunity in innate cells leads to modifications of functional cellular states allowing for a primed phenotype for exposure to a secondary pathogen. To better understand how innate immune cells change in the lung in response to the BCG vaccine, the current study analysed differential gene expression patterns in murine lung cells after BCG vaccination.
The aim of this study was to validate previous RNA sequencing findings by measuring genes identified with differential expression in innate immune cells after training with BCG. Lung cells enriched for non-lymphocytes or CD11b positive cells were chosen as cells of interest as they are enriched after BCG vaccination. RT-qPCR, flow cytometry and mass spectrometry were used to collectively analyse the expression of 20 genes of interest. These differentially expressed genes were linked to three main functional groups: 1) phagocytosis, 2) immune regulation, and 3) immune inflammation. Phagocytosis-linked genes generally indicated increased phagocytosis, whereas genes associated with immune regulation decreased. Variable alterations in immune inflammation occurred after BCG vaccination, however this study specifically identified two Signalling Lymphocyte Activation Molecules (SLAMF): slamf7 and slamf8 as being substantially increased after BCG vaccination. These genes encode proteins that can contribute to a strong inflammatory response especially within innate cells. This study successfully showed the differential gene expression patterns after BCG vaccination and validated the RNA sequencing data presented by Ryder, B. M. (2021). These findings uncover some potential protective mechanisms linked to BCG vaccination that could aid in the discovery of new pathways for improved TB vaccine development.