κ−λ− CVID patients also presented lower frequency of CD27+IgD–IgM– Switched Memory B cells (1.2%, IQR 0.4–5.0) when compared to both κ−λ+ and κ+λ+ groups (3.5%, IQR 1.0–5.9, u-test p = 0.050 and 2.5%, IQR 1.7–8.4, u-test p = 0.027, respectively) and the highest frequency of CD21low B cells among the CVID subgroups, with a significant difference in comparison to both κ−λ+ and κ+λ+ patients (9.0%, IQR 3.1–31.0 vs. 3.6, IQR 2.2–7.7, u-test p = 0.013, and vs 5.1%, IQR 1.9–6.5, u-test p = 0.030) (Figure 4B). Here, CD27 is linked to common variable immunodeficiency.