Choosing between an immortalised endothelial cell line and primary cells, and the same decision across tissues: why the endothelial cell lines on a catalogue behave differently from human brain microvascular endothelial cells or the microvascular endothelial cells taken from other beds, what a human astrocyte cell line, a human cardiomyocyte cell line and a human myoblast cell line each preserve and each lose, why a human fibroblast cell line or any immortalised fibroblast cell line is not a primary fibroblast, what a hacat cell line models in skin work, and where ips cell lines and a knockin cell line replace the question entirely

Deciding between primary cells and a line

1. Ask whether the property survives immortalisation. Immortalisation alters cell cycle control and frequently alters differentiation, barrier function and responsiveness. If your readout is one of those, the line may not show it. If your readout is a signalling event or a transport process that is preserved, the line is the practical choice.
2. Account for donor variability. Primary cells differ between donors, which is a nuisance in a mechanism experiment and the whole point in a study about population variation. Decide which of those you are doing, and where donors matter, use several and report them.
3. Respect the tissue bed. Cells from different vascular beds and different tissues differ substantially in marker expression, barrier tightness and response. A line from one bed is not a general model of that cell type, and the bed belongs in the description.
4. Check what the line retains, in your own hands. Suppliers state which markers and functions a line retains, usually at low passage under their conditions. Confirm the ones your conclusion depends on in your own culture, at the passage you use, before the line becomes the basis of a project.
5. Consider a derived model where the question is genetic. Where the question concerns a specific genotype, a differentiated stem-cell-derived model or a line edited at the locus of interest answers it more directly than any catalogue line. Both are slower and more expensive, and both remove the argument about whether the model carries the variant.

Barrier function is the usual casualty

Immortalised barrier-forming cells commonly form a weaker barrier than their primary counterparts, and the difference is largest in exactly the tissues where barrier work is most interesting. A line chosen for convenience in a barrier experiment can produce permeability results that no primary system reproduces.

If the readout is barrier integrity, establish what the line achieves under your conditions and say so, or use primary cells and accept the limits on numbers and lifespan. Reporting the absolute value rather than a relative change is what lets a reader judge the model.

Differentiated models from stem cells

Cells differentiated from induced pluripotent stem cells carry the donor's genotype and can be produced in quantity, which makes them attractive for tissues where primary cells are scarce. They are also frequently immature compared with adult tissue, and the maturation protocol matters as much as the starting material.

Treat the differentiation protocol as part of the model, characterise the resulting cells against the markers your conclusion depends on, and expect variability between differentiation batches. These are powerful models that reward being described precisely.

Edited lines and isogenic comparison

A line in which one locus has been altered against an otherwise identical background is the cleanest comparison available in cell culture, because everything except the variable is shared. Making one is a project in itself and buying one, where it exists, is usually cheaper.

Confirm the edit, keep the parental line banked alongside and use both in every experiment. An edited line compared with a different laboratory's parental stock loses most of what the edit was for.

Common questions

Primary cells or an immortalised line?

It depends on whether your readout survives immortalisation. Cell cycle control, differentiation and barrier function commonly do not; many signalling and transport processes do. Decide on the specific readout rather than on the class of model.

Is one endothelial line a general model?

No. Cells from different vascular beds differ in markers, barrier tightness and response, so the bed belongs in the description and a line from one bed does not stand for the rest.

When is an edited line worth the cost?

When the conclusion depends on one genetic difference. An isogenic pair shares everything except the variable, which is the cleanest comparison available; buy one where it exists rather than making it.

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