Altered interleukin-2 production by lymphocyte populations from bovine leukemia virus-infected cattle.

Abstract

The effects of bovine leukosis virus (BLV) on the phenotypic and functional characteristics of peripheral blood mononuclear cells were investigated. Whole blood differentials showed that persistently lymphocytotic (BLV+PL) dairy cattle had more lymphocytes and fewer neutrophils than the aleukemic seropositive (BLV+AL) or seronegative (BLV-) animals. Flow cytometric analyses of peripheral blood mononuclear cells indicated that the BLV+PL animals had more B lymphocytes, with a concomitant decrease in CD2 positive cells when compared with the BLV- group. Mononuclear cells from the BLV+AL animals also had fewer CD2 positive cells, but no differences in B lymphocytes were observed when compared with BLV- cattle. Peripheral blood mononuclear cells were used in blastogenesis assays to assess the functional ability of lymphocytes. Lymphocytes from BLV+PL animals had lower proliferative responses to concanavalin A and pokeweed mitogen when compared with cells from the BLV- or BLV+AL groups. The level of spontaneous blastogenesis in the absence of mitogenic stimulation was high for lymphocytes obtained from BLV+AL cattle. Cultures of lymphocytes obtained from BLV+PL animals produced greater amounts of interleukin-2 (IL-2) than BLV+AL and BLV- groups, although no differences were observed in the expression of IL-2 receptors. The development of uncontrolled lymphocytosis in BLV-infected cattle may result from an altered responsiveness to IL-2-regulated B-lymphocyte proliferation.