THP-1 clumping and PHA (Plates for stimulation?) - (Nov/21/2011 )

Hey guys,

I have started culturing THP-1 cells (maintained in RPMI with 10 % FBS, 1 % L-Glut, 1 % Pen/Strep) at 10⁴-10⁶ cells/mL and they are heavily clumping. Some people told me that they are clumping only when they're stressed, but I also found an old topic in this forum where people stated that this was normal.
I have attached a picture, but usually my clumps are much bigger (4x-5x the size pictured). So, all you THP-1 experts out there -is it normal?

Also, I have tried to stimulate/differentiate them by adding PHA at concentrations up to 600 nM. I used various cell densities from 10⁴-10⁶ cells in a 12 well plate and stimulated up to 36 h, but not all of them would stick to the ground. And also, the ones that did were not firmly attached (I have heard that some people trypsinized their stimulated THP-1 cells to get them off -I can do it just by tapping the bottom of my cell culture plate).

A friend of mine suggested it would have to do with the plates I'm using, since various brands differ in their material. I have tried Greiner (very bad) and TPP (not so bad) so far. Greiner Cell-Bind plates looked promising, but are quite expansive. Which brands are you using?

Thanks for your help!!

Aika

PMA, of course.

*temporary blackout*