Haemagglutination by bovine leukaemia virus

Bovine leukaemia virus (BLV) was found to agglutinate mouse erythrocytes. Under optimal conditions, including the use of neuraminidase-treated erythrocytes, 200 microgram/ml of BLV purified from the supernatant fluid of BLV-infected bat cells had haemagglutinating titres of about 512 units. BLV haemagglutination was drastically affected by pH and temperature; maximum agglutination occurred at pH 6 and 4 degrees C. That the BLV haemagglutinin is a glycoprotein was suggested by the fact that trypsin, potassium periodate or neuraminidase, but not lipid solvents or phospholipase C, significantly reduced the haemagglutinating (HA) activity of purified BLV. Furthermore, purified BLV glycoprotein of mol. wt. 51 000 (gp51) had HA activity. The receptors for BLV on mouse erythrocytes were inactivated by proteolytic enzymes but not by sodium deoxycholate or potassium periodate. Neuraminidase treatment of erythrocytes increase their agglutinability fourfold. Haemagglutination is a relatively sensitive test for detecting BLV glycoprotein because 0.4 microgram/ml of glycoprotein can be detected by this method. The pH and temperature sensitivity of the BLV HA reaction and specificity for mouse erythrocytes distinguish BLV from that of equine infectious anaemia virus and murine leukaemia virus, the other C type retroviruses known to have HA activity.