Impact of different Streptococcus pneumoniae on the secretion of interleukin and adhesin from THP-1 monocytes

Background: To investigate the secretion of interleukin-1β (IL-1β), IL-6, IL-10, IL-8, and soluble intercellular adhesin molecule 1 (sICAM-1) from THP-1 monocytes stimulated by different Streptococcus pneumoniae (S pneumoniae) strains.

Methods: Fifty-eight strains of S pneumoniae were collected: ATCC49619, 23 from sputum (sd-SP), 23 from blood (bd-SP), and 11 from cerebrospinal fluid (CSF; cd-SP). Such strains were cultured and suspended at 0.5 McFarland. THP-1 monocytes were cultured and resuspended at 5.0 × 10⁸ /L, which were stimulated by S pneumoniae for 4, 8, and 12 hours, respectively. The suspensions were analyzed for IL-1β, IL-6, IL-10, IL-8, and sICAM-1 using an ELISA method. The data were assayed with SPSS 19.0.

Results: Contrary to IL-10, the concentrations of IL-1β, IL-6, IL-8, and sICAM-1 all increased first and then decreased. IL-1β and sICAM-1 levels in the ATCC49619 group were both higher than all the clinical S pneumoniae groups (sd-SP, bd-SP, and cd-SP), IL-6 and IL-8 versa, and IL-10 equal. The difference among clinical S pneumoniae groups lay only in sICAM-1. cd-SP group showed lower sICAM-1 concentrations than sd-SP and bd-SP groups at both 4 and 8 hours. However, they became equal at 12 hours.

Conclusions: The secretion summit is 8 hours for IL-1β, IL-6, IL-8, and sICAM-1, bottom for IL-10. Different clinical S pneumoniae strains show similar ability to induce THP-1 cells secreting interleukins. However, cd-SP induces THP-1 cells secreting lower sICAM-1 than sd-SP and bd-SP, which may in turn facilitate its invasion into CSF.