In-Cell Western™ Assay Quality Assessment using Z’-Factor

If you have been following my posts for the past two months or so, you know we have been looking a great deal at In-Cell Western Assays (also called In-Cell ELISAs or plate-based immunofluorescent assays). On April 3, I explained what an ICW Assay is. From there we looked at examples of how In-Cell Westerns are used (studying apoptosis, for IC50 Determinations), seeding plates for In-Cell Westerns), ICW kits LI-COR® offers, and using cells in suspension, plate selection for ICW Assays, and cell lines that have been tested for use with this powerful immunocytochemical assay.

So you are hopefully ready to give this technique a try. When you do, it is important to assess the overall quality and reliability of the assay during In-Cell Western (ICW) assay optimization. The Z’-factor statistic provides a way to evaluate whether or not assay conditions (reagents, protocols, instrumentation, kinetics, and other conditions not directly related to the test compounds) are optimized. Z’-factor, introduced by Zhang et al., is a dimensionless value that represents both the variability and the dynamic range between two sets of sample control data.

Z’-factor experiments are performed on one or more ICW assay plates containing replicate wells designated for background subtraction, negative control samples, and positive control samples. Typically, negative control wells are those in which the cells receive an the appropriate treatment so as to elicit the lowest desired percent response (usually untreated cells); positive control wells are those in which the cells receive an appropriate treatment so as to elicit the maximum desired percent response; background wells are treated the same as the negative control wells, except primary antibody incubation is excluded.

Example of Z' Factor Data Plot

Here are some resources so that you can read more about the Z’-Factor, how to set up the experiments to assess it, and its importance in ensuring you have a high quality, reliable assay method:
Using the Z’-Factor Coefficient to Monitor Quality of Near-Infrared Fluorescent Cell-Based Assays
In-Cell Western Assay Quality Assessment Using Z’-Factor Data Sheet

Read more about Reproducibility and Precision in In-Cell Western Assays.

Cells in Suspension for Quantitative Cell Signaling Analysis using In-Cell Western™ Assays

In-Cell Western Assays - Fluorescent Immunoassays

So I’ve talked about how to ensure that suspension cells attach to plates, when to know you have a monolayer, and why round bottom plates are the best when doing In-Cell Western Assays with suspension cells in the 23-May-12 blog post. On 29-May-12 post, the post discussed how to wash your microplates so that you don’t lose cells plus some troubleshooting tips. I hope you found both of those posts helpful.

Here is the last post in this series on using non-adherent cells for ICW assays. These are a few additional questions you may have about using suspension cells for this powerful immunofluorescent assay.

  1. What suspension cell lines have been tested for use in In-Cell Westerns?
    Suspension cell lines tested include Jurkat, K-562, and THP-1.
  2. What pathways have been tested?
    Pathways tested include ERK activation and apoptosis using cleaved caspase-3 as a marker (Figure 1). A sample protocol can be downloaded here.

Do you have other questions? Super! Please contact us and let us know how we can help you in your research. And stop by this blog again for more technical tips and troubleshooting hints on other applications.

Anisomycin induced Apoptosis in Jurkat Cells

Figure 1. Anisomycin-induced apoptosis in Jurkat cells. The image represents a 96-well two-color In-Cell Western assay with the 700 and 800 nm channels detecting TO-PRO®-3 DNA staining and cleaved caspase-3 (Asp175), respectively. The image was scanned using the Odyssey® Sa Infrared Imaging system with scan setting of 200 μm resolution, focus offset of 3.5, and intensity of 3.5 (700 channel) and 4 (800 channel). Background (B) wells were incubated with a secondary antibody but no primary antibody. The graph represents normalized quantitative data demonstrating the increase in caspase-3 cleavage in response to anisomycin treatment for 3 hours in Jurkat cells.

Additional resources:
In-Cell Western Assays: FAQs when Using Suspension Cells
Complete Sample Protocol for PMA-Induced ERK Activation in Suspension Cell Lines
LI-COR BIO Website

More Essential Success Tips for Performing In-Cell ELISAs Using Non-Adherent Cells

Round Bottom Plates for In-Cell Western Assays

I mentioned in my post on 23-May, that the next few entries would be on more hints and tips of how to use non-adherent cells for In-Cell Western Assays – so here goes!

During my washing steps, cells are coming off the plates.

  1. Are you using the recommended round bottom 96-well plate (BD Biosciences, P/N 353077)?
    1. If no, cells will more easily detach from the flat bottom plates than the round bottom
      plates. The multi-channel pipettors will generate enough pressure when expelling liquid from the pipet to cause cell detachment when using flat bottom plates. Cells will detach even when pipetting down the sides of the wells.
    2. If yes, make sure you pipet down the sides of the wells and not directly onto the cells. If this doesn’t help, you may need to change your multi-channel pipettor because different brands of pipettors have different amount of pressure required to expel the liquid from the pipet. The recommended multi-channel pipettor is the 12-channel Finnpipette
      (Thermo Electron Corp, P/N 4610050).
  2. Are you shaking or rotating the plates at a moderate to high speed?
    1. If yes, gentler shaking/rotating is needed to prevent cells from detaching. Cells will detach. Set shaking or rotating speed to very low speed.
    2. If no, are you dumping the solutions straight from the plates? Dumping causes cells to
      detach. Either aspirate very slowly or manually pipet using the sides of the wells.

Why can’t I use the flat bottom 96-well plates?

  • LI-COR® Biosciences recommends using the round bottom 96-well plates for the reasons mentioned above.

When I scan an empty round bottom 96-well plate, I get lots of background noise.

  • The round bottom plate shows some background autofluorescence. The background fluorescence is relatively small compared to signal (about 200-fold difference depending on the intensity of the signal) and can be subtracted from the signal. It is necessary to include background wells containing cells and only the secondary antibodies in order to
    completely subtract away the background noise originating from the plate as well as from the non-specific binding of the secondary antibodies.

Here is a technical note on more FAQs on using non-adherent cells for In-Cell Western Assays. Or you can just stay tuned to my next blog post!

To your Research Success!

Using Non-adherent Cells for Fluorescent Immunoassays – Tips for Successful In-Cell Western™ Assays

In-Cell Western Assays - Fluorescent Immunoassays

You might be wondering if this powerful technique called In-Cell Western Assay can be used for your cell line because your cell line is non-adherent. Well, you are in luck! You CAN use suspension cells for ICW Assays – with some care and optimization.

Here are a few frequently asked questions. (see my next few blogs for more FAQs on using suspension cells for In-Cell Western Assays).

  1. How do you make non-adherent cells (suspension cells) attach to plates?

  2. A simple trick is to replace your complete media containing 10% serum (usually fetal bovine serum) with the same media minus the serum. Then allow the cells to sediment, forming a monolayer of cells within 10 minutes. Caution: Although cells appear attached to the plates, they are relatively loosely attached and therefore, extreme caution is required during solution-changing steps.

  3. How do I know that I have a monolayer?
    Method #1
  4. – Examine cells in the round bottom 96-well plates under a light microscope. The center of the wells should all have a small flat circular surface area where all the cells in that field are “in focus”. Moving the plane of focus, up or down, will cause cells to be “off focus”.
    Method #2 – Hold the round bottom 96-well plate under a light source. The monolayer should look opaque rather than transparent. Cells will not attach on top of the cell monolayer, so the opaqueness is due only to the monolayer.

  5. I cannot get a monolayer of cells. I get lots of spaces between cells. Is seeding 200,000 cells/well enough?
    Seeding 200,000 cells/well is more than enough to form a complete cell monolayer. It is necessary to allow the cells in serum-free media to sediment in the T75 flask (or other tissue culture plates) for approximately 30 minutes before counting cells using a hemacytometer. When cells in serum-free media are placed, for example, in a T7 tissue culture flask, a monolayer of cells will immediately begin to form on the bottom of the flask. This will dramatically decrease the number of cells in suspension that are available for plating.

    Note: Once a complete monolayer has formed on the plate, the rest of the cells will remain in suspension. Count these cells in suspension and the cells attached to the T75 flask can be discarded later.

Here is a complete sample protocol for PMA-induced ERK Activation in Suspension Cell Lines.

Check on the website pages on Tips for Using Cells in Suspension Cells for In-Cell ELISA Assays.