Fig. 1.

Low levels of neutralizing antibodies induced by the inactivated vaccine SARS-CoV Z-1 do not trigger ADE following the challenge. A Rhesus macaques were immunized intramuscularly with 2.5 μg beta-propiolactone-inactivated whole SARS-CoV Z-1 vaccine or PBS as control, and boosted on day 7. The blood was collected at 0, 4, 6, 7, 8, 9 weeks post-immunization. Titers were expressed as the reciprocal of the dilution at which 50% of the plaques reduced completely in the virus-wells. Data were presented as the mean ± S.E. for each group. B On day 10 or 14 post-infection, the surviving monkeys from the three groups were euthanized and necropsied; the lungs were collected and fixed using 4% formaldehyde, sectioned, and subjected to hematoxylin and eosin staining. Magnification, ×200. The arrows refer to the widening of alveolar septa and the infiltration of inflammatory cells. C The nasopharyngeal swabs were collected on day 2 post-challenge. The presence of SARS-CoV polymerase gene in the swabs was confirmed by RT-PCR. No. 1, 2, 3, 4, 8, 9, 10, and 11 lanes are from immunized group; No. 7, 12, 15, and 16 lanes are from virus control group; No. 5, 6, 13, 14 lanes are the swabs from negative control group; M, molecular size marker; PC, purified virus as positive control; NC, without cDNA template. D The virus titers of the sera from the monkeys whose samples showed positive results in virus isolation were detected on days 5 and 7 post-challenge by TCID₅₀. The values of the titer were expressed directly by the calculated number.