CD5 is dissociated from the B-cell receptor in B cells from bovine leukemia virus-infected, persistently lymphocytotic cattle: Consequences to B-cellreceptor-mediated apoptosis

Bovine leukemia virus (BLV), a retrovirus related to human T-cell leukemia virus types 1 and 2, can induce persistent nonneoplastic expansion of the C D5(+) B-cell population, termed persistent lymphocytosis (PL). As in human CD5(+) B cells, we report here that CD5,vas physically associated with the B-cell receptor (BCR) in normal bovine CD5(+) B cells. In contrast, in CD5( +) B cells from BLV-infected PL cattle, CD5 was dissociated from the BCR. I n B cells from PL cattle, apoptosis decreased when cells were stimulated wi th antibody to surface immunoglobulin M (sIgM), while in B cells from uninf ected cattle, apoptosis increased after sIgM stimulation. The functional si gnificance of the CDS-BCR association was suggested by experimental dissoci ation of the CDS-BCR interaction by cross-linking of CD5. This caused CD5() E cells from uninfected animals to decrease apoptosis when stimulated wit h anti-sIgM. In contrast, in CD5(+) B cells from PL animals, in which CD5 w as already dissociated from the BCR, there was no statistically significant change in apoptosis when CD5 was cross-linked and the cells were stimulate d,vith anti-sIgM. Disruption of CD5-BCR interactions and subsequent decreas ed apoptosis and increased survival in antigenically stimulated B cells may be a mechanism of BLV-induced FL.