Changes in antibody titers in cattle infected clinically and subclinically with bovine leukemia virus

Changes in titers of antibodies to protein and glycoprotein antigens of bovine leukemia virus (BLV) were investigated by immunodiffusion in two groups of cattle. In one group of cattle (10 head) which developed enzootic bovine leukosis during the observation period of 3 years, seven showed a gradual increase in antibody titers following a period of level antibody titers that persisted for several months to several years. The titer was finally eight to 32 times higher than the initial titer. The remaining three showed little change in titer. Of the 10 animals with tumors, three showed a decrease in the titer when they were in extremis. In contrast, in the second group of cattle (110 head), which were infected with BLV subclinically, the change in the titers during 1 and 3 years ranged from no change to four times the lowest titer that was observed during the period. Of the cattle which had a low level of antibody to one of the BLV antigens, a few became negative reactors to the respective antigen.