Figure 5. Depletion of alveolar macrophages impairs the protective activity of passively-transferred immune sera against BA.5 infection.

(a) Scheme for depletion of neutrophils and monocytes, passive transfer of immune sera, and BA.5 challenge. Wild-type C57BL/6 twelve-week-old male mice were administered 500 μg of anti-Gr-1 (Ly6C/Ly6G) or isotype control antibody at Day −3 and −1 by intraperitoneal injection. On Day −1, mice were also given 60 μL of naïve or immune sera by intraperitoneal injection. On Day 0, mice were inoculated with 10⁴ FFU of BA.5, and tissues were harvested for virological analysis on Day +3. (b-d) Analysis of depletion of immune cell subsets in blood of mice receiving anti-Gr-1 (Ly6C/Ly6G) or isotype antibody at 3 dpi. Summary of different cell types (b) based on the gating strategy (see Extended Data Fig 5a). Results are from two experiments (n = 6–10 mice per group; Mann-Whitney test with Bonferroni post-test correction, ns, not significant; **P < 0.01, ***P < 0.001****P < 0.0001). Representative flow cytometry dot plots showing depletion of neutrophils (c) and monocytes (d) with numbers indicating the cell population as a percentage of CD45⁺ cells. (e-f) Analysis of infectious viral burden by plaque assay at 3 dpi in nasal turbinates (e) and lungs (f) after BA.5 challenge (two experiments, n = 6–10 mice per group; Mann-Whitney test, ns, not significant). (g) Scheme for depletion of alveolar macrophages, passive transfer of immune sera, and BA.5 challenge. Wild-type C57BL/6 twelve-week-old male mice were administered control or clodronate liposomes at Day −3 by an intranasal route. On Day −1, mice were given 60 μL of naïve or immune sera by intraperitoneal injection. On Day 0, mice were inoculated with 10⁴ FFU of BA.5, and tissues were harvested on Day +3. (h) Analysis of depletion of immune cell subsets in lungs of mice receiving liposomes at 3 dpi. Summary of different cell types (h) based on gating strategy (see Extended Data Fig 5b). Results are from two experiments (n = 7–12 mice per group; Mann-Whitney test with Bonferroni post-test correction, ns, not significant; **P < 0.01, ***P < 0.001, ****P < 0.0001). (i) Representative flow cytometry dot plots showing depletion of alveolar macrophages after liposome administration with numbers indicating the cell population as a percentage of CD45⁺ cells. (j-k) Analysis of infectious viral burden by plaque assay at 3 dpi in nasal turbinates (j) and lungs (k) after BA.5 challenge (two experiments, n = 7–12 mice per group; Mann-Whitney test, ns, not significant; ****P < 0.0001).