Lipoprotein signal peptidase-deficient Streptococcus pneumoniae exhibits impaired Toll-like receptor 2-stimulatory activity.

Streptococcus pneumoniae is a causative agent of community-acquired pneumonia. Upon pneumococcal infection, innate immune cells recognize pneumococcal lipoproteins via Toll-like receptor 2 and induce inflammation. Here, we generated a strain of S. pneumoniae deficient in lipoprotein signal peptidase (LspA), a transmembrane type II signal peptidase required for lipoprotein maturation, to investigate the host immune response against this strain. Triton X-114 phase separation revealed that lipoprotein expression was lower in the LspA-deficient strain than in the wild-type strain. Additionally, the LspA-deficient strain decreased nuclear factor-κB activation and cytokine production in THP-1 cells, indicating impaired innate immune response against the strain.