ACE2 and systemic lupus erythematosus: In addition, pseudoneutralization and angiotensin-converting enzyme 2–RBD (ACE2-RBD) blocking assays revealed significantly lower neutralizing ability in serum derived from patients with SLE (as indicated by blocking of the ACE2-RBD interaction) compared with HC, suggesting decreased humoral protection against SARS-CoV-2 infection (Figure 1C; P < 0.0001, 2-way ANOVA).