2.4. Statistical analysis

Statistical analysis was performed using GraphPad Prism version 8.0 software. The Mann–Whitney test was used to compare differences between two independent data sets related to a single experimental condition (e.g., CD19⁺CD27⁻ vs. CD19⁺CD27⁺ unstimulated control B cells, or control vs. CVID single B-cell subpopulation stimulated with anti-BCR). The Wilcoxon test was used to compare differences between two paired groups of treatments (basal and post-stimulation conditions or each single stimulus with its combination with other stimuli). Correlation between variables was measured using Pearson’s correlation coefficient. A p-value less than 0.05 was considered statistically significant. Principal component analysis (PCA) was performed to evaluate relationships between the experimental variables studied and the patients’ B-cell deficiency according to the EUROclass classification. To this end, in the PCA, the categorical B-cell deficiency variable was converted to numerical data, as follows: healthy controls = 0, smB+ CVID patients = 1, and smB− CVID patients = 2. Variables were considered significantly loaded in the PCA when the loading value was above or below ±0.5.