EN
Appearance of IgG₁, IgG₂, IgM in blood serum was investigated in 12 calves, experimentally inoculated with BLV, immediately after birth. The titer of BLV antibodies, was also examined by means of ID and ELISA tests. An increase of IgG₂ fractions has been found in the first week after infection. However, this protein seems not to be a specific antibody. Properties of antibody have been revealed by the IgG₁ and IgM fractions. The results seem to indicate that IgG₁ fraction takes part in the precipitation observed in the ID test, whereas the IgM globulins are active in the ELISA test.