Class Switch Recombination Defects: impact on B cell maturation and antibody responses.

To assess how B cell phenotype analysis correlates with antigen responses in patients with class switch recombination defects (CSRD) we quantified memory B cells by flow-cytometry and immunized CSRD patients with the neoantigen bacteriophage phiX174 (phage). CSRD patients showed uniformly absent or markedly reduced switched memory B cells (IgM-IgD-CD27+). CD40L patients had reduced CD27+ memory B cells (both non-switched and switched). In NEMO patients, results varied depending on the IKKγ gene variant. Three of four AID patients had normal percentages of CD27+ memory B cells while CD27+IgM-IgD- switched memory B cells were markedly reduced in all AID patients. Antibody response to phage was remarkably decreased with lack of memory amplification and class-switching in immunized CD40L, UNG deficient, and NEMO patients. Distinct B-cell phenotype pattern correlated with abnormal antibody responses to a T-cell dependent neoantigen, representing a powerful tool to identify CSRD patients.