Lps does not trigger the inflammasome which is required for caspase 1 activation and cleavage of pro IL1b into its secreted and biologically active form.

In primary cells, I have seen LPS stimulate IL1b both intracellularly in monocytes and DCs as well as secreted in whole blood and PBMCs. Not sure why it wouldn't be seen in TGP1s though. Could it just be that you have too few cells per ml?

Try to add ATP ( 5 mM) for the last 30 minutes.

Can you see IL-1 beta release in fresh no stimulated by PMA THP-1? We see dramatic loss of pyrin expression during monocytes to macrophages differentiation ( in primary cells and also in PMA stimulated THP)  which correlates with cell ability to activate inflammasome.

Check cells for Mycoplasma.

You can try to use higher concentration of LPS. I use 1 ug/ml and the concentration of IL-1b is usually around 200 pg/ml.

In our experience THP-1's secrete high levels of IL-1ra. You may want to try a different pro-inflammatory stimuli or a combination of them.

Do your cells secrete any other cytokines in response to your stimulus? This would suggest that the LPS-stimulation is working per se.

As others have pointed out, IL-1b has to be a) transcriptionally induced, b) pro-IL-1b has to be processed by the inflammasome (which is NOT activated by LPS alone) and c) the cleaved protein has to be secreted.

You could try LPS+ATP (or LPS plus another known inflammasome activator, such as dsDNA etc.).

In this paper, ATP was used to induce inflammasome activation (cleavage of pro-caspase1 and subsequent cleavage of pro-IL1b) after priming with TLR-ligands (also LPS) J. Immunol. 2009;183;787-791

Good luck.

As stated by Jan Hosek, you stimulus might be low in your experimental protocol, since LPS activates the release of IL-1beta in activated monocytes (macrophages) and even in THP1, as stated by others and several papers in literature. It is also important to address how many cells you are using per mL. You should use at least 10^6 cells per mL. Otherwise, your ELISA kit will not be able to detect the small amount of IL-1beta secreted to the supernatant. 

Kind regards,

Raphael

LPS does induce IL-1b production (at least the mRNA level) in THP1 differentiated Macrophages. LPS  induces pro- IL1b which is accumulated inside the cells and need ed to be cleaved by caspases-1 to be released as IL-1b. I guess that the  reason that you were not able to detect the secreted form of IL-1b in the supernatant. Therefore, I would suggest you to lyse the cells and measure with ELISA kit. It worked for me though.

Undifferentiated THP-1 express little if any MD2, an accessory molecule for TLR4 stimulation with LPS. Invivogen has a graph that shows expression of a SEAP reporter in response to various toll ligands inTHP-1 cells with and without MD2. See attached link. If you aren't tied to TLR4 and just want an inflammatory stimulus. I use Pam3Csk4 routinely with THP-1 and see nice induction of IL-1b and TNFa.

http://www.invivogen.com/PDF/THP1_XBlue_MD2CD14_TDS.pdf

If you do LPS+ATP costimulation timing of the ATP preparation in your experiment is vital; dissolved ATP hydrolizes within minutes;

http://www.ncbi.nlm.nih.gov/pubmed/25729382

Thanks for the tips! I tried with 5mM ATP and now it worked!