Figure 4. Immune mechanism of protection: T-cell depletion, adoptive transfer and antibody passive transfer.
a, Monoclonal rat anti-mouse anti-CD4, CD8 or CD4/CD8/CD90 were used to deplete T cells in SΔCD and control vaccinated mice (n = 4) as described previously23. Mice were then challenged with SARS-CoV 48 h later. Viral replication in the lungs was measured as described in Fig. 3. Data represent mean ± s.e., and no statistically significant difference was observed between groups depleted as shown. b, Lack of protection against SARS-CoV replication in the lungs after adoptive T-cell transfer from vaccinated mice. Each naive mouse (n = 4) received 3 × 107 purified T cells from a donor mouse confirmed to respond to the vaccine (immune) or from a non-immune mouse (control). The recipient mice were challenged 24 h after adoptive T-cell transfer. Viral titre in lungs was measured as described in Fig. 3. There was no statistically significant difference between these two groups using the non-parametric Mann–Whitney two-tailed t-test (P = 0.49). c, Protection against SARS-CoV replication in the lungs after passive transfer of immune IgG from vaccinated mice. Purified IgG from SΔCD or control vaccinated donor mice (n = 4) was passively transferred into recipient naive mice (n = 4). Serum from recipient mice was collected one day before challenge, and neutralization was confirmed using the S pseudotyped lentiviral vector (left panel). Recipient mice (n = 4 per group) were challenged 24 h after IgG transfer with 104 TCID50 SARS-CoV and SARS-CoV replication was measured as described in Fig. 3. The non-parametric two-tailed t-test (Mann–Whitney) revealed a statistically significant difference of P = 0.0286 between these two groups (right panel).