I want to test whether my anti-HA monoclonal antibodies can inhibit the membrane fusion step of influenza virus entry, but we don't have any resources for syncytium formation assay with HA-expressing cell line.

It seems to me that in one of the articles I saw an alternative method using red blood cells, but I can't remember what article it was.

I've found this protocol, but still not sure if it suitable for antibodies:

"As previously described (Zhu et al., 2011), an equal volume of serially 2-fold diluted CBS1194 in PBS was mixed with 40 μL PBS or virus stock in a 96-well plate. After incubating the virus-compound mixture at room temperature for 30 min, 80 μL of 2% chicken erythrocytes prewarmed to 37 °C was added. The mixture was incubated at 37 °C for another 30 min. Hemolysis was triggered by adding 80 μL of sodium acetate (0.5 M, pH 5.0). The mixture was mixed well and incubated at 37 °C for 30 min for HA acidification and hemolysis. The plates were then centrifuged at 1200 rpm for 6 min, and 200 μL of supernatant was transferred to another 96-well plate. The OD540 was read using an EnVision plate reader (PerkinElmer)."

Thanks for all the suggestions!