CD40LG and acquired polycythemia vera: The median titer of SARS-CoV-2-specific IgM was higher in the PV group with comorbidities (0.27S/co [IQR, 0.04–15.66]) than in the UV group with comorbidities, but the difference was not statistically significant (adjusted P = 0.056) (see Fig. 2C).