With the simple aid of a magnetic field, magnetic beads pre-coupled with biotinylated proteins are well-suited for highly efficient immunocapture, biopanning and virus capture. Apart from these common applications, beads can also be used in antibody-dependent cellular phagocytosis (ADCP) assay to evaluate the phagocytic potential of activated effector cells, an experiment commonly performed in tumor or virus studies.

   Fig.1. Antibody-mediated cellular phagocytosis (ADCP) of protein-coupled beads.

A recent study of HIV-1 reported the use of fluorescent bead-based flow cytometric assay to quantify cellular phagocytosis of GP41-coupled beads by monocytes. In the standard bead ADCP assay they performed, protein-coupled fluorescent beads are incubated with antibodies to be adequately opsonized prior to addition to phagocytic cells, and the beads uptak by cells are analyzed by flow cytometry. To further differentiate the surface-attached beads from the intracellular beads, they incorporated a Specific Hybridization Internalization Probe (SHIP) which selectively inactivate the SHIP fluorescence of the attached beads but not of those truly internalized. In this way, the number of beads phagocytosed by single effector cell can also be accurately identified from the fluorescence level. In summary, they reported the method being highly efficient and repeatable.

In bead-based ADCP assay，detection of the phagocytosed beads can be performed with fluorescence technology or electronic microscopy (EM). ACROBiosystems has developed a list of beads products that are suitable to be used in ADCP assays and conveniently visualized with EM. These 2um beads can provide reliable simulation data by mimicking antigen presentation on different tumor cells or virus-infected cells. Additionally, using bead-based assay to measure Fc-mediated phagocytosis has advantages over real cell assays for being inexpensive, convenient to manipulate and can be stored for a long period of time.

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Reference:

 1.Duchemin M, Tudor D,  Cottignies-Calamarte A, Bomsel M. Antibody-Dependent Cellular Phagocytosis of  HIV-1-Infected Cells Is Efficiently Triggered by IgA Targeting HIV-1 Envelope  Subunit gp41. Front Immunol. 2020 Jun 9;11:1141. doi: 10.3389. Retrieved from https://www.frontiersin.org/articles/10.3389/fimmu.2020.01141/full

  2.Lloyd, Y.M., Ngati, E.P., Salanti, A. et  al. A versatile, high through-put, bead-based phagocytosis assay  for Plasmodium falciparum . Sci Rep 7, 14705  (2017). Retrieved from https://doi.org/10.1038/s41598-017-13900-4