Genetic determination of the effect of post-translational modification on the innate immune response to the 19 kDa lipoprotein of Mycobacterium tuberculosis.

Background: The 19 kDa lipoprotein of Mycobacterium tuberculosis (MTB) is an important target of the innate immune response. To investigate the effect of post-translation modification of this protein on innate recognition in the context of the whole bacillus, we derived a recombinant M. tuberculosis H37Rv that lacked the 19 kDa gene (Delta19) and complemented this strain by reintroduction of the 19 kDa gene into the chromosome as a single copy to produce Delta19::19. We also reintroduced the 19 kDa gene in two modified forms that lacked motifs for acylation (Delta19::19NA) and O-glycosylation (Delta19::19NOG).

Results: Both acylation and O-glycosylation were necessary for the protein to remain within the cell. IL-1 Beta secretion from human monocytes was significantly reduced by deletion of the 19 kDa gene (p < 0.02). Complementation by the wild type, but not the mutagenised gene reversed this phenotype. The effect of deletion and complementation on IL-12p40 and TNF secretion was less marked with no statistically significant differences between strains. Although deletion of the 19 kDa reduced apoptosis, an effect that could also only be reversed by complementation with the wild type gene, the results were variable between donors and did not achieve statistical significance.

Conclusion: These results confirm in the context of the whole bacillus an important role for post-translational modification of the 19 kDa on both the cellular location and immune response to this protein.