An In Vitro Assay for Evaluating the Immunomodulatory Impact of Monocytes on Leukocyte Proliferation

Take a multi-well plate with adherent mesenchymal stem cell, or MSC, culture.

Add peripheral blood mononuclear cells, or PBMCs, and incubate.

MSCs secrete hepatocyte growth factor, inducing monocytes to acquire an immunomodulatory phenotype, producing interleukin-10, or IL-10.

Transfer the PBMC-containing supernatant to a tube.

Add antibody-coated magnetic beads binding to monocyte surface marker CD14.

Use a magnetic separator to isolate the CD14+ monocytes, and add them to multi-well plate wells in increasing concentrations.

Introduce fluorescent dye CFSE-labeled effector CD4+ T cells.

Add antibody-conjugated microbeads binding specifically to T cell surface markers CD3 and CD28, activating the cells.

In the control well-lacking monocytes, activated T cells proliferate, with each cell division decreasing CFSE fluorescence intensity in daughter cells.

However, in co-cultures, MSC-induced monocytes secrete IL-10, suppressing effector T cell proliferation.

Using flow cytometry, observe fewer T cells exhibiting reduced CFSE fluorescence intensities with increasing monocyte concentrations, indicating the suppression of effector T cell proliferation by MSC-induced monocytes.

To perform an effector suppression assay, begin by setting up an MSC-PBMC co-culture with 2.5 x 10⁶ PBMCs, co-cultured with 250,000 MSCs to ensure enough MSC co-cultured PBMCs for subpopulation selection.

After 48 to 72 hours at 37 degrees Celsius, select the MSC-induced immunomodulatory leukocytes of interest with the appropriate magnetic beads. Then, add CFSE-labeled allogeneic CD4-positive T cells in 1 milliliter of complete leukocyte medium per well, at various experimental ratios.

Next, add anti-CD3/28-conjugated microbeads at a 1-to-1 bead-to-cell ratio to stimulate the CD4-positive T cells. On the third day of co-culture, assess the proliferation of the CFSE-labeled CD4-positive T cells by flow cytometry.