Heating serum to 56°C for 30 minutes was used in the past to inactivate the complement system for immunoassays. Heat activation has also been reported to inactivate other undetermined inhibitors of cell growth in culture. However, the practice is labor-intensive and expensive. The protocol must be followed exactly as too high a temperature or too long a time may destroy some growth factors.

On occasion heat inactivation of serum is used because of previous history in the laboratory or for the convenience of stocking only one kind of serum.

In past years, Coriell used all heat-inactivated serum for its cell cultures to inactivate the complement protein found in newborn calf serum. Since we have changed to fetal bovine serum, we find that heat inactivation is not necessary for most cell lines. Occasionally we do find a differentiated cell line that grows better in heat inactivated serum, but for most lymphoblast and fibroblast lines it does not seem to make a difference whether the serum is heat inactivated or not.

The online Coriell catalogs list the serum that was used to create the initial cell line (either heat inactivated or "not inactivated"). As we make an expansion lot of the cell line, the culture conditions are changed to reflect the current practice ("not inactivated" for most cell lines).

If your laboratory normally stocks heat-inactivated serum, you can probably use it without a problem. In fact, many of the labs that use Coriell cell lines do use heat-inactivated serum.