A recent clinical trial showing significant benefits of IgM-enriched immunoglobulin preparation for patients with pneumonia and lower levels of endogenous IgM (Brunner et al., 2013; Cavazzuti et al., 2014; Wand et al., 2016; Welte et al., 2018; Kalvelage et al., 2019; Willuweit et al., 2019) further supports this notion. Here, CD40LG is linked to susceptibility to pneumonia measurement.