Characterization of B1-cells during experimental leukomogenesis

Background. Bovine leukemia causes a significant polyclonal expansion of CD5⁺ , IgM⁺ B lymphocytes, known as persistent lymphocytosis (PL), in approximately 30% of infected cattle. However, it is not yet clear what happens to this subpopulation of B cells in the early period of infection of animals.

Purpose. Quantitative characterization of IgM⁺ and CD5⁺ B cells during the immune response, which can provide important information on the mechanisms of lymphocyte priming in BLV infection.

Material and methods. The experiment used BLV-negative calves of black-motley breed at the age of 8 months (n = 11). Animals (n = 8) were intravenously injected with blood of a BLV-positive cow. Control calves (n = 3) were injected with saline. Studies were performed before and after infection on days 5, 7, 14, 21, 28 and 65 of the immune response. The determination of the number of B-lymphocytes in the blood was carried out by the method of immunoperoxidase staining based on monoclonal antibodies to IgM, CD5.

Results. As a result of the studies, it was found that the level of CD5⁺ B cells increases on the 14th day of the primary immune response, characterized by polyclonal proliferation of CD5⁺ B cells, which are the primary target for BLV. Our research data confirm that in the lymphocytes of experimentally infected cattle, surface aggregation of IgM and CD5 molecules on B-lymphocytes is absent.

Discussion. It is known that the wave-like nature of IgM synthesis, which was shown in previous studies, depends on a subpopulation of B1 cells. After 7 days of the immune response, IgM⁺ and CD5⁺ cells do not correlate, which shows their functional difference. The increase in CD5⁺ cells is probably not associated with B cells, but with T cells differentiating under the influence of the virus.

Conclusions. A subset of B1 cells is the primary target of cattle leukemia virus. The 65th day of the immune response is characterized by the expansion of IgM⁺ B cells, a decrease in the number of CD5⁺ cells and a uniform distribution of receptors around the perimeter of the cells.