If two cells are of different densities, can they be separated through density gradient centrifugation? or any other method? Similarly if two human cell lines are of different sizes can they be separated by using some filters?
Separating cells by size is difficult. I do not recommend filtration - cells do deform, and unless the size difference is very large, you cannot resolve them.
Density is a much better way to separate cell types. There are several ways to do this. Depending on the density difference, you can use Percoll step gradients. Pharmacia [now GE Helathcare] used to sell this. I do not know if they still do.
If the density of one cell line is greater than 1.077 gm/ml and the other less, you can use standard Ficoll-Paque. We do this all the time to separate mononuclear cells from erythrocytes and neutrophilsin blood samples.
An old method for separating cells by density difference was centrifugal elutriation. Beckman made special rotors and chambers for this. By controlling g forces and elutriation flow rate, very minor differences can be resolved. I have seen this system used to separate different stages of cell cycle of cell lines. The problem is that this is old technology [35 years+] and I do not know if anyone still does this kind of work.
Another method may be MACS [Miltenyi]. If one cell line has a surface antigen the other lacks, and there is a bead kit available, you can incubate you cell mixture with the beads, and run them over a magnetic column. Even lacking specific beads, if you have an antibody, there are secondary antibody beads and even anti-biotin beads.
I haven't had to separate to cell line but FACS sorting sounds like the right way to go . Even better if you have receptors differentially expressed between your cell lines you can use antibodies too.
Thank you all for your answers. Hi Gary nicely explained. Do you have any idea regarding after cell separation through percoll method, can they be used to grow again in cell culture media?