I'm doing phagocytosis assay using J774.A1 macrophages. I've had no problems growing them in both cell culture flasks and 24wells-plates until now. For the last several months the cells would grow fine in flasks but every now and then when seeded into 24-wells plates they would detach from the bottom, and some of them even have "necrosis-like" cell lysis (even before infection). I used DMEM+10%FBS+L-glutamine+antibiotic as growth medium. Any suggestions would be very helpful to me.