Hello Kingkarn Rachadet

THP-1 cells are sensitive to cell density. The recommended seeding density is between 3-7 x 10^5 cells/ml. Generally, 5 x10^5 cells /ml is used. THP-1 cells grow better in conditioned media. Therefore whenever you passage the cells, leave 1-2ml of old media and add fresh media to the culture. Use RPMI-1640 media supplemented with 10% FBS and 2-mercaptoethanol to a final concentration of 0.05 mM.

If you have just thawed the cells recently, then you need to increase the FBS content to 20% for the first two to three passages, then you can switch over to 10% FBS for successive passaging.

Sometimes cells may clump. But if they are growing fine and have a normal morphology it should not be a problem. You need to remove dead cells if they are present as sometimes these dead cells could be the cause of clumping.

To remove dead cells and debris use low-speed centrifugation. Gently centrifuge the cell suspension at a low speed (for instance, 100-150 x g) for a short time (say, 5-10 minutes) to pellet live cells. Then discard the supernatant containing the dead cells and debris. Dead cells and cell debris are generally lighter and less dense than live cells. Centrifugation at low speed allows the live cells to pellet down, while the lighter dead cells and debris remain in the supernatant.

Best,