Haemadsorption and haemagglutination

Many viruses have antigens which adsorb to and cross-link red blood cells. When the antigens are expressed on the surface of infected cells, these cells will adsorb red blood cells (haemadsorption). 

Alternatively when virions and red cells interact a network is formed and the suspension agglutinates, i.e. the red cells are precipitated. There is some specificity as to which viruses will agglutinate red cells from which animal, but once the combination is known haemagglutination forms a quick assay for virus titre. 

Blood is collected in a heparinised syringe and the red cells washed three times in 0.85% saline by sedimentation at 200g for 10 min and resuspension. They are finally resuspended in 200 volumes 0.85% saline. 

The assay is most conveniently carried out in a microtitre plate (Fig. 3.2) and the dispensing may be done by hand or using automatic equipment available from Titertek (Flow Labs. Ltd. Appendix 3). 

25fil of 0.85% saline or PBS is dispensed into a series of wells in the micro titre plate and 25/wl of virus suspension is added to the first well and mixed (1 in 2 dilution). 25/i.l is then removed from the first well and mixed in the second well (1 in 4 dilution) and so on to give dilutions up to 1 in 2048. 25jal of red blood cell suspension is now added, mixed, and left, either at 4°C, room temperature or 37°C until haemagglutination has occurred (1-2 h). 

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