After using PMA (50 ng/mL) 48 hours to differentiate my THP-1 into macrophage, it was observed that have many clear bubbles in it.

I wonder if it is normal or not and does it indicate my cells were not healthy?

I planing to induce these cell to M1 by using LPS, can it still be working?(planning test IL-1beta by using ELISA kit)

I will be pleasure if someone could give me some advices!

(should I try to lower the PMA concentration?)