Technical library

Yes. Alternative fixation methods can be used.
If Saccomanno Fixation Solution is not available, the cells can be fixed using:

• 4.5% neutral buffered formalin, or
• Paraformaldehyde

Both alternatives are suitable for fixation prior to chondrogenic, adipogenic, and osteogenic staining of MSCs.

Yes, differentiation of M1 macrophages from PBMCs in 96‑well plates is possible.
At PromoCell, this setup has not been formally validated internally. However, multiple users have reported successful differentiation of mononuclear cells into M1 macrophages using a 96‑well plate format.
 
User‑reported conditions
Based on customer feedback:

• Plating density: Approximately 1 × 10⁶ PBMCs per well, without prior determination of the monocyte content, has been reported to work well.
• Plate format: Standard 96‑well tissue culture plates, coated with collagen type I
• Working volume: Typically 100 µl per well

Under these conditions, users observed efficient differentiation of mononuclear cells into macrophages in the 96‑well format.
The standard protocol for the differentiation of macrophages from PBMC is provided in the corresponding PromoCell Application Note.

This has not been tested by PromoCell and would need to be evaluated by the customer.
PromoCell’s M2 Macrophage Generation Medium XF is substantially different from RPMI‑based media. Therefore, we cannot predict whether switching to RPMI or RPMI + M‑CSF after differentiation would maintain cell viability, phenotype, or function.
Based on our experience, successful long‑term culture of M2 macrophages has only been validated within the PromoCell system using our media.

In the PromoCell macrophage differentiation system, the polarization into M1 or M2 macrophages is completed within 7 days, which is consistent with reports in the literature and protocols used by other researchers.
 
Why the protocol spans 10 days
The PromoCell protocol includes an additional 2–3 days for optional macrophage activation. These extra days are intentionally included to improve overall culture performance.
Even if you aim to obtain non‑activated M1 or M2 macrophages, PromoCell does not recommend shortening the full 10‑day protocol, because:

• A medium change on days 8–10 promotes re‑attachment of previously floating cells
• This results in higher cell viability
• Overall cell yield is increased

The most likely reason is an insufficient washing step during monocyte enrichment by adherence.
During macrophage differentiation from PBMCs, monocyte purification relies on adherence, while lymphocytes (including CD3⁺ T cells) should be removed during the washing steps.
 
Critical point in the protocol
The three washing steps described in the PromoCell protocol are essential. If washing is not performed thoroughly:

• Non‑adherent lymphocytes may remain
• These cells can persist and later be observed attached to or associated with macrophages

When performed correctly, the adherence‑based purification yields a monocyte population of >90% purity, which minimizes T‑cell carryover.

In general, cryo­preserved macrophages should be activated for approximately 24 hours, or at least overnight, to reliably measure cytokine release.
If cytokine induction is not optimal under your specific experimental conditions, the activation time can be shortened or extended accordingly to optimize the response.

No. PromoCell has not tested macrophage attachment on fibronectin‑coated glass surfaces.
Therefore, no validated data are available on macrophage growth or attachment behavior under these specific conditions.

The recommended seeding density of 100,000 cells/cm² for PromoCell M1 macrophages is required to achieve a confluent cell layer, as these cells do not proliferate after seeding.

Reducing the seeding density:
Yes. If a fully confluent monolayer is not essential for your assay, the seeding density can be reduced by a factor of 3 to 5.

No. The Cytokine Mix M1 and Cytokine Mix M2 should not be subjected to additional freeze-thaw cycles.
Repeated freezing and thawing can lead to degradation and loss of biological activity of the cytokines, which may negatively affect macrophage polarization and experimental reproducibility.
To ensure optimal performance, the cytokine mixes should be thawed only once and used immediately.

No. Based on negative customer feedback, PromoCell strongly discourages the use of bead baths for thawing Normal Human Cells.
The use of bead baths can lead to reduced cell viability or significantly slower cell growth after thawing.

Recommended alternative
If a conventional water bath is not available and only a bead bath is present in the lab:

• Place a beaker filled with water into the bead bath.
• Ensure the water temperature is exactly 37°C, verified with a thermometer placed in the water.
• Follow the PromoCell thawing protocol described in the Product Manual.