CD5 Is Dissociated from the B-Cell Receptor in B Cells from Bovine Leukemia Virus-Infected, Persistently Lymphocytotic Cattle: Consequences to B-Cell Receptor-Mediated Apoptosis

Abstract

ABSTRACT Bovine leukemia virus (BLV), a retrovirus related to human T-cell leukemia virus types 1 and 2, can induce persistent nonneoplastic expansion of the CD5 + B-cell population, termed persistent lymphocytosis (PL). As in human CD5 + B cells, we report here that CD5 was 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. In B cells from PL cattle, apoptosis decreased when cells were stimulated with antibody to surface immunoglobulin M (sIgM), while in B cells from uninfected cattle, apoptosis increased after sIgM stimulation. The functional significance of the CD5-BCR association was suggested by experimental dissociation of the CD5-BCR interaction by cross-linking of CD5. This caused CD5 + B cells from uninfected animals to decrease apoptosis when stimulated with anti-sIgM. In contrast, in CD5 + B cells from PL animals, in which CD5 was already dissociated from the BCR, there was no statistically significant change in apoptosis when CD5 was cross-linked and the cells were stimulated with anti-sIgM. Disruption of CD5-BCR interactions and subsequent decreased apoptosis and increased survival in antigenically stimulated B cells may be a mechanism of BLV-induced PL.