Protocol workflow for whole blood memory B cell phenotyping and vaccine-specific antibody quantification

Recurrent infections in children often prompt evaluation for primary immunodeficiency diseases, particularly those affecting humoral immunity. Assessment of memory B cell subsets and vaccine-specific antibody responses provides critical insight into long-term protective immunity. While peripheral blood mononuclear cell (PBMC) isolation is common, direct whole blood staining offers faster processing, reduced cell loss, and better preservation of fragile B cell populations. This comprehensive protocol describes a standardised whole blood flow cytometry method for memory B cell phenotyping, alongside ELISA-based measurement of vaccine-specific antibody titres as part of assessing children with recurrent infections.