Fig. 5. SARS-CoV-2 antibody responses are CD4⁺ T cell–dependent but not required for viral control in the respiratory tract.

C57BL/6 mice were depleted of either CD4⁺ or CD8⁺ or both T cells, and at indicated days p.i., binding and neutralizing antibody response against SARS-CoV-2 B.1.351 spike, RBD, and nucleocapsid were measured by electrochemiluminescent multiplex immunoassay and reported as arbitrary units per ml (AU/ml) against SARS-CoV-2. IgG antibody responses were measured against (A) Spike, (B) RBD, and (C) Nucleocapsid. (D) The 50% inhibitory titer (FRNT₅₀) on the FRNT was measured at day 10 p.i. and day 28 p.i. The dotted line in the FRNT assay represents the maximum concentrations of the serum tested (1/20). A two-way ANOVA statistical test was performed. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001; no symbol, not significant.