B-cell replication history and somatic hypermutation status identify distinct pathophysiologic backgrounds in common variable immunodeficiency
Common variable immunodeficiency disorder (CVID) is the most prevalent form of primary idiopathic hypogammaglobulinemia. Identification of genetic defects in CVID is hampered by clinical and immunologic heterogeneity. By flow cytometric immunophenotyping and cell sorting of peripheral B-cell subsets of 37 CVID patients, we studied the B-cell compartment at the B-cell subset level using the κ-deleting recombination excision circle assay to determine the replication history and the Igκ-restriction enzyme hot-spot mutation assay to assess the somatic hypermutation status. Using this approach, 5 B-cell patterns were identified, which delineated groups with unique replication and somatic hypermutation characteristics. Each B-cell pattern reflected an immunologically homogenous patient group for which we proposed a different pathophysiology: (1) a B-cell production defect (n ∇ 8, 18%), (2) an early peripheral B-cell maturation or survival defect (n ∇ 4, 11%), (3) a B-cell activation and proliferation defect (n ∇ 12, 32%), (4) a germinal center defect (n ∇ 7, 19%), and (5) a postgerminal center defect (n ∇ 6, 16%). The results of the present study provide for the first time insight into the underlying pathophysiologic background in 5 immunologically homogenous groups of CVID patients. Moreover, this study forms the basis for larger cohort studies with the defined homogenous patient groups and will facilitate the identification of underlying genetic defects in CVID.