Sometimes when we buy in batches of human AB serum, they're clear and the typical golden/yellow colour. But sometimes the serum comes through quite thick and cloudy. Does anyone have any idea what might be in the serum?
This happens with serum from both Sigma and Lonza. We can filter the serum to clear it but it takes a lot of filtering, first through 30um cell strainers, then through 0.8um vacuum filters and finally 0.45um filters. To clear a 500ml batch of serum requires 5 or 6 cell strainers and then 4 or 5 0.8um and 0.45um vacuum filters.
I've also tried spinning it to clear it. After 20 minutes at 2000g, there is a thick white or creamy layer on the top of the serum but this doesn't clear it and it still requires filtering, just through fewer filters.
Any advice on what is making the serum cloudy and how best to remove it?
Chris, I begun speculating on causes assuming small batches of HSA. floating materials sounds like low-density material perhaps lipid? Worse case scenarios? 1. possible bacterial contamination - dispose of sample. 2. proteins could be denatured and aggregated (filter or reject). 3. Proteins solutions can undergo reversible aggregation so allowing to reach room temperature and gentle agitation will restore pristine appearance. Consider storage conditions - avoid agitation and physical causes (too low temperatures) during storage. Batch to batch variations in supplied material could be referred to supplier - small changes to additives, stabilizers added by manufacturer will sometimes lead to differences as you describe.
Hi Richard,
Yes, I wondered if it was lipid material. It is more common in batches made from smaller numbers of donors which suggests it might be high lipid levels in one donor.
We've ruled out bacterial or fungal contamination by culturing T cell lines for over 4 weeks with no contamination issues using un-filtered serum. I'd also think it unlikely that it's denatured protein, partly as it's unlikely to spin out so easily and also the performance of the serum is not affected by the precipitate. Finally, whatever is causing what we see is thermostable and unaffected by storage at -80oC, -20oC, +4oC, +25oC or +37oC.
I think it's likely to be donor related but just wondered if anyone else had seen it!
Even though if have never used HSA, I am pretty sure that it is lipid. Because probably any other substance i can imagine would pellet at the bottom and wouldn't float on the surface after centrifugation.
Have you ever asked the supplier what it is? I guess they should know it for sure.
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