The Serum BAFF level is related to IFN-γ content, is increased in those with fewest SMB cells, and the lowest serum IgA levels. (A) BAFF and IFN-γ. BAFF was significantly related to the amount of IFN-γ in sera of 98 paired CVID sera (Spearman r = −0.3120, P = 0.002). (B) BAFF and isotype SM B cells. Serum BAFF was significantly increased with CVID subjects with very reduced SM B cells, <2% as compared to those subjects with 2% or more of these B cells (Mann–Whitney test, P = 0.0001) or normal controls. (C) BAFF and serum IgA. BAFF levels were inversely related to baseline serum IgA in 95 paired CVID serum samples (Spearman correlation, r = −0.2065; P = 0.04).