Binding of the human urinary colony-stimulating factor to sterile filtration membranes

Marked loss of colony stimulating activity was noted when the highly purified human urinary colony stimulating factor (CSFHU-5) dissolved in 0.1 M Tris-HCl buffer (pH 7) was passed through ethylene oxide sterilized Millipore filters. The addition of 0.5 mg/ml polyethylene glycol (PEG) or 10 mg/ml bovine serum albumin (BSA) to the CSFHU solutions resulted in almost complete protection against the CSF loss. A less pure fraction (CSFHU-2) did not lose activity upon filtration. More than 90% of the 125I-CSFHU dissolved in 0.1 M Tris-HCl buffer (pH 7) bound to the ethylene oxide sterilized Millipore filters. The addition of PEG or BSA to the 125I-CSFHU solutions resulted in almost complete prevention of 125I-CSFHU binding to the membranes. These findings indicate that Millipore membranes can bind significant quantities of the highly purified CSFHU, and the addition of PEG to all buffer systems is a useful way to prevent the CSF loss throughout the purification.