Preparation and development of equine hyperimmune globulin F(ab')2 against severe acute respiratory syndrome coronavirus.

Aim: The resurgence of severe acute respiratory syndrome (SARS) is still a threat because the causative agent remaining in animal reservoirs is not fully understood, and sporadic cases continue to be reported. Developing high titers of anti-SARS hyperimmune globulin to provide an alternative pathway for emergent future prevention and treatment of SARS.

Methods: SARS coronavirus (CoV)F69 (AY313906) and Z2-Y3 (AY394989) were isolated and identified from 2 different Cantonese onset SARS patients. Immunogen was prepared from SARS-CoV F69 strain. Six health horses were immunized 4 times and serum was collected periodically to measure the profile of specific IgG and neutralizing antibodies using indirect enzyme-linked immunosorbent assay and a microneutralization test. Sera were collected in large amounts at the peak, where IgG was precipitated using ammonium sulphate and subsequently digested with pepsin. The product was then purified using anion-exchange chromatography to obtain F(ab')2 fragments.

Results: The specific IgG and neutralizing antibody titers peaked at approximately week 7 after the first immunization, with a maximum value of 1:14210. The sera collected at the peak were then purified. Fragment of approximately 15 g F(ab')2 was obtained from 1litre antiserum and the purity was above 90% with the titer of 1:5120, which could neutralize the other strain (SARS-CoV Z2-Y3) as well.

Conclusion: This research provides a viable strategy for the prevention and treatment of SARS coronavirus infection with equine hyperimmune globulin, with the purpose of combating any resurgence of SARS.