Hemadsorption is the ability of cells infected with an enveloped virus containing a hemagglutinin in its envelope to adsorb red blood cells. As the virus reproduces, these hemagglutinins (glycoproteins) are inserted into the plasma membrane of the infected cell. These modified areas of the cell surface are the sites at which progeny virus particles will mature. If agglutinable red blood cells are brought into contact with hemagglutinin-containing surfaces of cultured cells, the red blood cells will specifically bind to the infected cells. The hemadsorption phenomenon is particularly useful in detecting infection by viruses that cause little cytopathic effect.
Figure 1 shows a hemadsorption assay performed on bovine fetal spleen cells infected with parainfluenza virus type 3. 72 hours post infection the infected cells were washed with phosphate-buffered saline. 0.5% bovine red blood cells were incubated with the infected cells for 10 minutes, washed with phosphate-buffered saline, and then observed under a 20x objective.
Figure 2 is a magnified, labeled version of the above micrograph. Arrows point to blood cells adsorbing to both cells and the glass where cells have detached from the glass leaving behind viral envelope proteins.