The majority of those who heat inactivate serum products for cell culture probably do not consider whether or not this step is still desirable; they are simply following an original protocol. At one time, heat inactivation was considered necessary because of concerns over possible contaminants in serum. Things have changed. Today, many feel that exposing serum to heat degrades valuable biomolecules, such as growth factors, vitamins, and amino acids–and is no longer generally advisable.
The practice of heat inactivating serum was originally developed when only serum from adult animals was available for cell culture. Adult serum contains various immune factors, particularly serum complement, which may inhibit or destroy cells under certain conditions.