Corticosteroid immunosuppression and monoclonal antibody-mediated CD5+ T lymphocyte depletion in normal and equine infectious anaemia virus-carrier horses.

This research investigates methods of controlling chronic equine infectious anaemia (EIA) lentiviral infection in horses, through the use of monoclonal antibody (MAb) to deplete CD5+ T lymphocytes or by immunosuppression with corticosteroids. The findings reveal the potential use of MAb for exploring the role of T lymphocyte subpopulations in disease control.

Monoclonal Antibody (MAb) Treatment

• The study specifically attempted to deplete CD5+ T lymphocytes in horses suffering from EIA through MAb treatment.
• MAb treatment was administered intravenously at doses ranging between 25 to 50 mg/day over a period of 11 days.
• Horses treated with murine IgG2a anti-CD5 MAb HB19A demonstrated successful depletion of peripheral blood CD5+ T lymphocytes during the treatment period.
• A residual population of CD2+ T lymphocytes was, however, maintained in the treated horses. These cells did not express CD5 but contained either CD4 or CD8 markers.

Response of CD5- T Lymphocytes

• The residual CD5- T lymphocytes demonstrated normal responses in vivo to intradermal inoculation with phytohaemagglutinin, and in vitro to stimulation by allogeneic leukocytes in mixed lymphocyte reactions. This suggests these cells maintained their functional capacity despite the treatment.
• Ongoing study of these CD5- T lymphocytes might contribute to understanding the role of different T lymphocyte subpopulations in disease control.

Immunosuppression Treatment with Corticosteroids

• When horses infected with EIA virus were immunosuppressed with corticosteroids (1 mg/kg body weight/day, intravenously for 9 days), recrudescent EIA viraemia was detected in 6 out of 11 horses (55%) and renewed disease was noted in 9 out of 11 horses (82%).
• In contrast, normal horses that received corticosteroid treatment did not develop clinical disease, suggesting a potential link between the EIA infection and the adverse effects in corticosteroid-treated horses.

Research Implications

• The use of murine IgG2a MAbs targeting equine lymphocyte antigens was proven helpful for in vivo investigation of the functional roles of specific T lymphocyte subpopulations in the management of EIA or other crucial equine diseases.