I am trying to establish a dose-response relationship with different concentrations of LPS on differentiated THP-1 cell-secreted TNFa and IL-1b. However, I am finding that all the concentrations I used (15-1000 ng/mL) produced similar increases in TNFa and IL-1b. This looks like an on-off response rather than a graded response as described in the literature. I am not sure why I am getting this maximum response even with the lowest concentrations used. I would appreciate any suggestions. Thank you!
My guess is that you have reached the plateau of cytokine production at a very low dose of LPS. I would double check to make sure your dilutions are correct first (you are already using a decent range of doses but something may be off). I would then proceed to use an even lower dose range. LPS requires a lot of vortexing-- be sure to do so while making serial dilutions.
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