Dynamics of cell-associated viremia and antibody response during the early phase of lentivirus infection in sheep

Abstract

Objective - To determine patterns of cell-associated viremia and antibody responses during the early phase of ovine lentivirus (OvLV) infection in sheep. Animals - 18 neonatal lambs. Procedures - 12 lambs were inoculated intratracheally with OvLV within 24 hours after birth; 6 lambs were inoculated with noninfected cell culture supernatant. Degree of cell-associated viremia was measured every other week for 16 weeks by use of a limited dilution assay. Antibody responses to OvLV transmembrane (TM) and p25 proteins were determined weekly by use of a recombinant ELISA. Neutralizing antibody responses were measured before and 8 and 16 weeks after inoculation. Results - Degree of cell-associated viremia peaked between 2 and 6 weeks after inoculation and then decreased. For inoculated lambs, mean anti-p25 titer peaked 5 weeks after inoculation then slowly declined, whereas mean anti-TM and neutralizing anti-body titers increased steadily. Over time, mean degree of cell-associated viremia was negatively correlated with mean anti-TM titer. Maximum individual degree of cell-associated viremia was positively correlated with maximum individual anti-TM titer. Conclusions - Results suggest that after experimental inoculation, OvLV replicates actively for several weeks and that an increase in anti-TM titer coincides with a decrease in degree of cell-associated viremia. Although the role antibodies play in protecting against lentivirus infection remains uncertain, understanding the dynamics of the antibody response may have important implications for diagnosis of OvLV infection, and antibodies may prove to be valuable markers for prediction of infection and disease.