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Predominantly antibody deficiencies (PADs) are the most prevalent primary immunodeficiencies, but their B-cell defects and underlying genetic alterations remain largely unknown. We investigated patients with PADs for the distribution of 41 blood B-cell and plasma cell (PC) subsets, including subsets defined by expression of distinct immunoglobulin heavy chain subclasses. Blood samples from 139 patients with PADs, 61 patients with common variable immunodeficiency (CVID), 68 patients with selective IgA deficiency (IgAdef), 10 patients with IgG subclass deficiency with IgA deficiency, and 223 age-matched control subjects were studied by using flow cytometry with EuroFlow immunoglobulin isotype staining. Patients were classified according to their B-cell and PC immune profile, and the obtained patient clusters were correlated with clinical manifestations of PADs. Decreased counts of blood PCs, memory B cells (MBCs), or both expressing distinct IgA and IgG subclasses were identified in all patients with PADs. In patients with IgAdef, B-cell defects were mainly restricted to surface membrane (sm)IgA+ PCs and MBCs, with 2 clear subgroups showing strongly decreased numbers of smIgA+ PCs with mild versus severe smIgA+ MBC defects and higher frequencies of nonrespiratory tract infections, autoimmunity, and affected family members. Patients with IgG subclass deficiency with IgA deficiency and those with CVID showed defects in both smIgA+ and smIgG+ MBCs and PCs. Reduced numbers of switched PCs were systematically found in patients with CVID (absent in 98%), with 6 different defective MBC (and clinical) profiles: (1) profound decrease in MBC numbers; (2) defective CD27+ MBCs with almost normal IgG 3 + MBCs; (3) absence of switched MBCs; and (4) presence of both unswitched and switched MBCs without and; (5) with IgG 2 + MBCs; and (6) with IgA 1 + MBCs. Distinct PAD defective B-cell patterns were identified that are associated with unique clinical profiles. [ABSTRACT FROM AUTHOR]

Background Humoral immunocompetence develops stepwise throughout life and contributes to individual susceptibility to infection, immunodeficiency, autoimmunity, and neoplasia. Immunoglobulin heavy chain (IgH) isotype serum levels can partly explain such age-related differences, but their relationship with the IgH isotype distribution within memory B-cell (MBC) and plasma cell (PCs) compartments remains to be investigated. Objective We studied the age-related distribution of MBCs and PCs expressing different IgH isotypes in addition to the immature/transitional and naive B-cell compartments. Methods B-cell and PC subsets and plasma IgH isotype levels were studied in cord blood (n = 19) and peripheral blood (n = 215) from healthy donors aged 0 to 90 years by using flow cytometry and nephelometry, respectively. Results IgH-switched MBCs expressing IgG 1 , IgG 2 , IgG 3 , IgA 1 , and IgA 2 were already detected in cord blood and newborns at very low counts, whereas CD27 + IgM ++ IgD + MBCs only became detectable at 1 to 5 months and remained stable until 2 to 4 years, and IgD MBCs peaked at 2 to 4 years, with both populations decreasing thereafter. MBCs expressing IgH isotypes of the second immunoglobulin heavy chain constant region (IGHC) gene block (IgG 1 , IgG 3 , and IgA 1 ) peaked later during childhood (2-4 years), whereas MBCs expressing third IGHC gene block immunoglobulin isotypes (IgG 2 , IgG 4 , and IgA 2 ) reached maximum values during adulthood. PCs were already detected in newborns, increasing in number until 6 to 11 months for IgM, IgG 1 , IgG 2 , IgG 3 , IgA 1 , and IgA 2 ; until 2 to 4 years for IgD; and until 5 to 9 years for IgG 4 and decreasing thereafter. For most IgH isotypes (except IgD and IgG 4 ), maximum plasma levels were reached after PC and MBC counts peaked. Conclusions PC counts reach maximum values early in life, followed by MBC counts and plasma IgH isotypes. Importantly, IgH isotypes from different IGHC gene blocks show different patterns, probably reflecting consecutive cycles of IgH isotype switch recombination through life. [ABSTRACT FROM AUTHOR]