TNFRSF13B encodes TACI, a B-cell specific TNF receptor superfamily member. Both biallelic and monoallelic TNFRSF13B mutations were identified in patients with common variable immunodeficiency disorders. The genetic complexity and variable clinical presentation of TACI deficiency prompted us to evaluate the genetic, immunological, and clinical condition in a cohort of 50 individuals with TNFRSF13B alterations, following screening of 564 unrelated patients with hypogammaglobulinemia. The mutational spectrum includes 13 new sequence variants. The most frequent TNFRSF13B variants (C104R and A181E)(n=39, 6.9%) were also present in a heterozygous state in 2% of 675 healthy controls. All patients with biallelic mutations had hypogammaglobulinemia and nearly all showed a loss of APRIL binding. However, the majority (n=41; 82%) of the 50 TACI-deficient patients carried monoallelic changes in TNFRSF13B. Presence of a heterozygous mutation was associated with antibody deficiency (P = 1e-05, relative risk 3.6). Heterozygosity for the most common mutation C104R was associated with disease (P = 8e-04, relative risk 4.2). Furthermore, heterozygosity for C104R was associated with low numbers of IgD(-)CD27(+) B cells (P =.019), benign lymphoproliferation (P = 1e-05), and autoimmune complications (P =.001). These associations indicate that C104R heterozygosity increases the risk for CVID and influences the clinical presentation.

Myeloid and plasmacytoid dendritic cells (MDCs, PDCs) play critical roles in B cell development and antibody production. Primary antibody deficiencies in humans might therefore reflect a deficit in MDCs and/or PDCs. We tested this hypothesis by measuring dendritic cell (DC) subset numbers in patients with common variable immunodeficiency (CVID), X-linked agammaglobulinaemia (XLA) and specific polysaccharide antibody deficiency (SPAD). In CVID both MDC and PDC numbers were markedly reduced. There was a graded reduction in all DC subsets across the Freiburg CVID groups (memory B cell classification) and the greatest deficit was seen in group Ia cases with the most severe disease. In contrast, MDC numbers alone were reduced in XLA whilst in SPAD the DC numbers were normal. In CVID, the number of MDCs correlated strongly with switched memory B cell percentage and total B cell count. Low numbers of DCs correlated with a greater incidence of autoimmunity, splenomegaly and granulomatous disease, and a higher incidence of clinical complications. Measurement of MDC and PDC numbers provides both prognostic information for clinical management and classification of CVID cases for future pathogenetic research. Our findings are consistent with the hypothesis that deficits in DC subsets are a critical feature in CVID.

The heterogeneity of common variable immunodeficiency (CVID) calls for a classification addressing pathogenic mechanisms as well as clinical relevance. This European multicenter trial was initiated to develop a consensus of two existing classification schemes based on flowcytometric B cell phenotyping and the clinical course. The clinical evaluation of 303 patients with the established diagnosis of CVID demonstrated a significant coincidence of granulomatous disease, autoimmune cytopenia and splenomegaly. Phenotyping of B cell subpopulations confirmed a severe reduction of switched memory B cells in most of the patients. This reduction was associated with a higher risk for splenomegaly and granulomatous disease. An expansion of CD21(low) B cells marked patients with splenomegaly. Lymphadenopathy was significantly linked with transitional B cell expansion. Based on these findings and pathogenic consideration of B cell differentiation we suggest an improved classification for CVID (EUROClass) separating patients with nearly absent B cells (<1%), severely reduced switched memory B cells (<2%) and expansion of transitional (>9%) or CD21(low) B cells (>10%). While the first group contains all patients with severe defects of early B cell differentiation, severely reduced switched memory B cells indicate a defective germinal center development as found in ICOS or CD40L deficiency. The underlying defects of expanded transitional or CD21(low) B cells remain to be elucidated. This trial is registered at http://www.uniklinik-freiburg.de/zks/live/uklregister/Oeffentlich.html as UKF000308.

Adenosine deaminase (ADA) deficiency is an inherited disorder which leads to elevated cellular levels of deoxyadenosine triphosphate (dATP) and systemic accumulation of its precursor, 2-deoxyadenosine. These metabolites impair lymphocyte function, and inactivate S-adenosylhomocysteine hydrolase (SAHH) respectively, leading to severe immunodeficiency. Enzyme replacement therapy with polyethylene glycol-conjugated ADA is available, but its efficacy is reduced by anti-ADA neutralising antibody formation. We report here carrier erythrocyte encapsulated native ADA therapy in an adult-type ADA deficient patient. Encapsulated enzyme is protected from antigenic responses and therapeutic activities are sustained. ADA-loaded autologous carrier erythrocytes were prepared using a hypo-osmotic dialysis procedure. Over a 9-yr period 225 treatment cycles were administered at 2-3 weekly intervals. Therapeutic efficacy was determined by monitoring immunological and metabolic parameters. After 9 yr of therapy, erythrocyte dATP concentration ranged between 24 and 44 mumol/L (diagnosis, 234) and SAHH activity between 1.69 and 2.29 nmol/h/mg haemoglobin (diagnosis, 0.34). Erythrocyte ADA activities were above the reference range of 40-100 nmol/h/mg haemoglobin (0 at diagnosis). Initial increases in absolute lymphocyte counts were not sustained; however, despite subnormal circulating CD20(+) cell numbers, serum immunoglobulin levels were normal. The patient tolerated the treatment well. The frequency of respiratory problems was reduced and the decline in the forced expiratory volume in 1 s and vital capacity reduced compared with the 4 yr preceding carrier erythrocyte therapy. Carrier erythrocyte-ADA therapy in an adult patient with ADA deficiency was shown to be metabolically and clinically effective.

We have analysed data from 150 patients initially classified as having CVID. About 10% had laboratory abnormalities suggesting known single gene disorders (eg: hyper-IgM syndrome), and in a few a genetic defect has been confirmed. We have attempted to sub-classify the remaining patients by analysis of their circulating lymphocytes. B lymphocyte markers have been used to estimate the numbers of circulating immature and class switched B cells; there is an association between the presence of high relative numbers of immature circulating B cells, splenomegaly and autoimmune disease. About 25% of CVID patients have a moderate CD4+ T lymphopenia, sometimes with a relative expansion of CD8+ T cells. About 30% of CVID patients have persistent relatively high levels of circulating CD8+ T cells binding immunogenic peptides from EBV or CMV. Many of these patients also have high relative numbers of circulating CD8+ perforin positive T cells, and there is evidence that these cells may be responsible for neutropenia or inflammatory bowel disease in some patients. The clinical spectrum of CVID is diverse, with some patients suffering from few infections, and over 50% have evidence of structural lung damage. About 25% of UK patients have chronic inflammation in various organs, particularly the lungs, liver and spleen, often with granulomatous changes. Steroids are used to treat many of the patients with chronic inflammatory complications, although trials are in progress with anti-TNF agents. The incidence of these inflammatory complications is different between countries, being rare in Sweden. Attempts to correlate clinical phenotypes with the laboratory abnormalities described above have been disappointing, suggesting that unknown genetic factors unrelated to the cause of the immunodeficiency determine the complications; attempts to identify some of these factors will be discussed. Finally a provisional scheme to sub classify CVID patients according to lymphocyte abnormalities will be presented, the purpose being to focus the screening of candidate genes causing CVID to specific subsets of patients.

We show that at least half of patients with common variable immunodeficiency (CVID) have circulating CD8(+) T cells specific for epitopes derived from cytomegalovirus (CMV) and/or the Epstein-Barr virus (EBV). Compared to healthy age-matched subjects, more CD8(+) T cells in CVID patients were committed to CMV. Despite previous reports of defects in antigen presentation and cellular immunity in CVID, specific CD4(+) and CD8(+) T cells produced interferon (IFN)-gamma after stimulation with CMV peptides, and peripheral blood mononuclear cells secreted perforin in response to these antigens. In CVID patients we found an association between a high percentage of circulating CD8(+) CD57(+) T cells containing perforin, CMV infection and a low CD4/CD8 ratio, suggesting that CMV may have a major role in the T cell abnormalities described previously in this disease. We also show preliminary evidence that CMV contributes to the previously unexplained severe enteropathy that occurs in about 5% of patients.

We review recent developments in the pathogenesis of the major immunodeficiencies, the pathogens involved, and new diagnostic and treatment options. Early diagnosis and prophylaxis are the mainstays in the current management of these immunological disorders. New advances, including the use of cytokines and growth factors, molecular diagnosis and a better understanding of the immunopathogenesis of infections, are discussed.

Monocyte-derived dendritic cells (MdDCs) from many patients with common variable immunodeficiency (CVID) have been shown recently to have reduced expression of surface molecules associated with maturity. Using flow cytometry and confocal microscopy, we now show that this is due to a partial failure to fix Class II DR molecules on the surface during procedures that induce full maturation in vitro in cells from normal subjects. Major histocompatibility complex (MHC) class I, CD86 and CD83 expression were expressed normally, but CD40 was reduced. These abnormalities are unlikely to be due to prior in vivo exposure of monocytes to lipopolysaccharide (LPS), as addition of LPS to monocytes from normal subjects in vitro caused a different pattern of changes. CVID MdDCs retained Class II DR in the cytoplasm during maturation, showed increased internalization of cross-linked Class II DR surface molecules and were unable to polarize DR within a lipid raft at contact sites with autologous lymphocytes. These cells retained some features of monocytes, such as the ability to phagocytose large numbers of fixed yeast and fluorescent carboxylated microspheres and expression of surface CD14. These abnormalities, if reflected in vivo, could compromise antigen presentation and may be a fundamental defect in the mechanism of the antibody deficiency in a substantial subset of CVID patients.

The phenotype of common variable immunodeficiency (CVID) is characterized by recurrent infections owing to hypogammaglobulinemia, with deficiency in immunoglobulin (Ig)G and at least one of IgA or IgM. Family studies have shown a genetic association between CVID and selective IgA deficiency (IgAD), the latter being a milder disorder compatible with normal health. Approximately 20-25% of CVID cases are familial, if one includes families with at least one case of CVID and one of IgAD. Nijenhuis et al described a five-generation family with six cases of CVID, five cases of IgAD, and three cases of dysgammaglobulinemia. We conducted a genome-wide scan on this family seeking genetic linkage. One interval on chromosome 4q gives a peak multipoint LOD score of 2.70 using a strict model that treats only the CVID patients and one obligate carrier with dysgammaglobulinemia as affected. Extending the definition of likely affected to include IgAD boosts the peak multipoint LOD score to 3.38. The linkage interval spans at least from D4S2361 to D4S1572. We extended our study to a collection of 32 families with at least one CVID case and a second case of either CVID or IgAD. We used the same dominant penetrance model and genotyped and analyzed nine markers on 4q. The 32 families have a peak multipoint LOD score under heterogeneity of 0.96 between markers D4S423 and D4S1572 within the suggested linkage interval of the first family, and an estimated proportion of linked families (alpha) of 0.32, supporting the existence of a disease-causing gene for autosomal-dominant CVID/IgAD on chromosome 4q.European Journal of Human Genetics advance online publication, 26 April 2006; doi:10.1038/sj.ejhg.5201634.

Polymorphisms in exon 1 of the MBL-2 gene, resulting in reduced plasma levels of mannose binding lectin, were significantly overrepresented in 23 patients with primary antibody deficiency and culture-proven mycoplasma infections (P = 0.0038). This association persisted with the inclusion of a further nine suspected (doxycycline-responsive) cases (P = 0.0087). The lectin was shown to bind to three strains of mycoplasma.