Defective integration of activating signals derived from the T cell receptor (TCR) and costimulatory molecules in both CD4+ and CD8+ T lymphocytes of common variable immunodeficiency (CVID) patients

Altered Transcriptome Response in PBMCs of Czech Adults Linked to Multiple PFAS Exposure: B Cell Development as a Target of PFAS Immunotoxicity

While the immunomodulation effects of per- and polyfluoroalkyl substances (PFASs) are described on the level of clinical signs in epidemiological studies (e.g., suppressed antibody response after vaccination), the underlying mechanism has still not been fully elucidated. To reveal mechanisms of PFAS exposure on immunity, we investigated the genome-wide transcriptomic changes of peripheral blood mononuclear cells (PBMCs) responding to PFAS exposure (specifically, exposure to PFPA, PFOA, PFNA, PFDA, PFUnDA, PFHxS, and PFOS). Blood samples and the chemical load in the blood were analyzed under the cross-sectional CELSPAC: Young Adults study. The overall aim of the study was to identify sensitive gene sets and cellular pathways conserved for multiple PFAS chemicals. Transcriptome networks related to adaptive immunity were perturbed by multiple PFAS exposure (i.e., blood levels of at least four PFASs). Specifically, processes tightly connected with late B cell development, such as B cell receptor signaling, germinal center reactions, and plasma cell development, were shown to be affected. Our comprehensive transcriptome analysis identified the disruption of B cell development, specifically the impact on the maturation of antibody-secreting cells, as a potential mechanism underlying PFAS immunotoxicity.

Single-cell Atlas of common variable immunodeficiency shows germinal center-associated epigenetic dysregulation in B-cell responses

Common variable immunodeficiency (CVID), the most prevalent symptomatic primary immunodeficiency, displays impaired terminal B-cell differentiation and defective antibody responses. Incomplete genetic penetrance and ample phenotypic expressivity in CVID suggest the participation of additional pathogenic mechanisms. Monozygotic (MZ) twins discordant for CVID are uniquely valuable for studying the contribution of epigenetics to the disease. Here, we generate a single-cell epigenomics and transcriptomics census of naïve-to-memory B cell differentiation in a CVID-discordant MZ twin pair. Our analysis identifies DNA methylation, chromatin accessibility and transcriptional defects in memory B-cells mirroring defective cell-cell communication upon activation. These findings are validated in a cohort of CVID patients and healthy donors. Our findings provide a comprehensive multi-omics map of alterations in naïve-to-memory B-cell transition in CVID and indicate links between the epigenome and immune cell cross-talk. Our resource, publicly available at the Human Cell Atlas, gives insight into future diagnosis and treatments of CVID patients.

Common variable immunodeficiency (CVID) is the most prevalent primary immunodeficiency. Here the authors perform single-cell omics analyses in CVID-discordant monozygotic twins and show epigenetic and transcriptional alterations associated with activation in memory B cells.

Seeking Relevant Biomarkers in Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is the most common symptomatic form of primary immunodeficiency. More than 50% of patients in some series suffer from autoimmune or inflammatory complications (the "CVID+" phenotype), and these are not adequately addressed by current treatments. Despite major advancements in genetics, the pathogenesis of the CVID+ phenotype has remained unexplained for most patients, necessitating the need for relevant biomarkers in both the clinic and research settings. In the clinics, reduced isotype-switched memory B cells (≤ 0.55% of B cells) and reduced T cells (CD4) can be utilized to identify those with increased complication risks. Additionally, condition-specific markers have also been suggested for lymphoma (normal or elevated IgM) and progressive interstitial lung disease (increased BAFF, normal or elevated IgM). Additional biomarkers have provided insights into disease pathogenesis, demonstrating wider systemic inflammation (increased LBP, sCD14, and sCD25; expanded ILC3), mucosal defects (increased zonulin, I-FABP), and perhaps reduced anti-inflammatory capability (reduced HDL) in CVID. Most recently, efforts have revealed elevated circulating bioactive bacterial DNA levels - marking microbial translocation and potentially linking the causation of multiple inflammatory changes previously observed in CVID. The implementation of high throughput profiling techniques may accelerate the search of relevant biomarker profiles in CVID and lead to better clinical risk stratification, revealing disease insights, and identifying potential therapeutic targets.

Atypical patterns of STAT3 phosphorylation in subpopulations B cells in patients with common variable immunodeficiency

BACKGROUND

Common Variable Immunodeficiency (CVID) is a heterogeneous disorder characterized by defective B cell differentiation and antibody production. Interleukin (IL)-21 activates STAT3, a potent regulator of B cell differentiation into plasma cells. We have studied the phosphorylation of STAT3 in CVID patients and its contribution to B cells subsets.

METHODS

We studied 23 CVID patients and 14 healthy donors (HD), determining pSTAT3 in naïve and memory B cells, stimulated with IL-21 at 15 and 60 min.

RESULTS

pSTAT3 was increased in total (p = 0.044), naïve (p = 0.023), and memory (p = 0.001) B cells at 60 min in CVID patients compared with HD. We classified patients by the percentage of isotype-switched memory B cells. We observed an increase in pSTAT3 at 60 min in memory B cells in both CVID groups of patients (p = 0.026, p = 0.007, respectively). Interestingly, the analysis of each group individually; demonstrated that patients with decreased memory B cells exhibited an increase in pSTAT3 at 60 min (p = 0.023), while HD had an expected decrease in pSTAT3 (p = 0.045).

CONCLUSION

CVID patients showed an increased atypical of pSTAT3, which could affect the differentiation of B cells. Further studies in the IL-21 pathway are necessary to understand how this alteration could promote differentiation defects in patient B cells.

B cells promote CD8 T cell primary and memory responses to subunit vaccines

The relationship between B cells and CD4 T cells has been carefully studied, revealing a collaborative effort in which B cells promote the activation, differentiation, and expansion of CD4 T cells while the so-called “helper” cells provide signals to B cells, influencing their class switching and fate. Interactions between B cells and CD8 T cells are not as well studied, although CD8 T cells exhibit an accelerated contraction after certain infections in B-cell-deficient mice. Here, we find that B cells significantly enhance primary CD8 T cell responses after vaccination. Moreover, memory CD8 numbers and function are impaired in B-cell-deficient animals, leading to increased susceptibility to bacterial challenge. We also show that interleukin-27 production by B cells contributes to their impact on primary, but not memory, CD8 responses. Better understanding of the interactions between CD8 T cells and B cells may aid in the design of more effective future vaccine strategies.

Generating cytotoxic CD8 T cell responses with vaccines can greatly improve their efficacy, but inducing adequate numbers of these cells can be challenging. Klarquist et al. reveal that the magnitude, persistence, and function of CD8 T cell vaccine responses depend on B cells.

Preserved Cellular Immunity Upon Influenza Vaccination in Most Patients with Common Variable Immunodeficiency

BACKGROUND

Vaccination against influenza is recommended for patients with common variable immunodeficiency (CVID), although humoral immune responses in these patients are impaired and the evidence of effective T-cell responses in CVID is not well established.

OBJECTIVE

To determine plasmablast and T-cellular vaccination responses against influenza in patients with CVID.

METHODS

Patients with CVID and healthy controls were vaccinated with the quadrivalent vaccine Influsplit Tetra 2018/2019. Before and 1 week after vaccination plasmablasts and circulating inducible costimulator-expressing T follicular helper cells were measured to determine positive vaccine responses in these patients. In addition, antigen-specific T cells were determined by their upregulation of CD25 and OX40 after in vitro restimulation with the vaccine.

RESULTS

Most healthy controls but only 1 patient with CVID mounted a positive humoral immune response, measured by an increase in plasmablasts 1 week after vaccination. In contrast, most patients with CVID showed an increase in inducible costimulator⁺ T follicular helper cells and/or an increase in antigen-specific CD25⁺OX40⁺ T cells 1 week after vaccination, demonstrating a positive T-cellular immune response.

CONCLUSIONS

Despite the remaining challenge of accurately assessing the complexity of T-cell responses, the recommendation of vaccinating patients with CVID against influenza is reasonable.

Clonal and constricted T cell repertoire in Common Variable Immune Deficiency

We used high throughput sequencing to examine the structure and composition of the T cell receptor β chain in Common Variable Immune Deficiency (CVID). TCRβ CDR3 regions were amplified and sequenced from genomic DNA of 44 adult CVID subjects and 22 healthy adults, using a high-throughput multiplex PCR. CVID TCRs had significantly less junctional diversity, fewer n-nucleotide insertions and deletions, and completely lacked a population of highly modified TCRs, with 13 or more V-gene nucleotide deletions, seen in healthy controls. The CVID CDR3 sequences were significantly more clonal than control DNA, and displayed unique V gene usage. Despite reduced junctional diversity, increased clonality and similar infectious exposures, DNA of CVID subjects shared fewer TCR sequences as compared to controls. These abnormalities are pervasive, found in out-of-frame sequences and thus independent of selection and were not associated with specific clinical complications. These data support an inherent T cell defect in CVID.

Common Variable Immunodeficiency and Circulating TFH

CD4+ T follicular helper cells (T_FH) were assessed in adult patients with common variable immune deficiency (CVID) classified according to the presence of granulomatous disease (GD), autoimmunity (AI), or both GD and AI (Group I) or the absence of AI and GD (Group II). T_FH lymphocytes were characterized by expression of CXCR5 and PD-1. T_FH were higher (in both absolute number and percentage) in Group I than in Group II CVID patients and normal controls (N). Within CXCR5+CD4+ T cells, the percentage of PD-1 (+) was higher and that of CCR7 (+) was lower in Group I than in Group II and N. The percentages of Treg and T_FH reg were similar in both CVID groups and in N. T_FH responded to stimulation increasing the expression of the costimulatory molecules CD40L and ICOS as did N. After submitogenic PHA+IL-2 stimulation, intracellular expression of T_FH cytokines (IL-10, IL-21) was higher than N in Group I, and IL-4 was higher than N in Group II. These results suggest that T_FH are functional in CVID and highlight the association of increased circulating T_FH with AI and GD manifestations.

Immunologic assessment and KMT2D mutation detection in Kabuki syndrome

Kabuki or Niikawa-Kuroki syndrome (KS) is a rare disorder with multiple malformations and recurrent infections, especially otitis media. This study aimed to investigate the genetic defects in Kabuki syndrome and determine if immune status is related to recurrent otitis media. Fourteen patients from 12 unrelated families were enrolled in the 9-year study period (2005-2013). All had Kabuki faces, cleft palate, developmental delay, mental retardation, and the short fifth finger. Recurrent otitis media (12/14) and hearing impairment (8/14) were also more common features. Immunologic analysis revealed lower memory CD19+ cells (11/13), lower memory CD4+ cells (8/13), undetectable anti-HBs antibodies (7/13), and antibody deficiency (7/13), including lower IgA (4), IgG (2), and IgG2 (1). Naïve emigrant lymphocytes, lymphocyte proliferation function, complement activity, and superoxide production in polymorphonuclear cells were all normal. All the patients had KMT2D mutations and 10 novel mutations of R1252X, R1757X,Y1998C, P2550R fs2604X, Q4013X, G5379X, E5425K, R5432X, R5432W, and R5500W. Resembling the phenotype of common variable immunodeficiency, KS patients with antibody deficiency, decreased memory cells, and poor vaccine response increased susceptibility to recurrent otitis media. Large-scale prospective studies are warranted to determine if regular immunoglobulin supplementation decreases the frequency of otitis media and severity of hearing impairment.

Cytokines in common variable immunodeficiency as signs of immune dysregulation and potential therapeutic targets - a review of the current knowledge

Common variable immunodeficiency (CVID) is characterized by low levels of circulating immunoglobulins and compromised specific antibody response leading to frequent infections. Cytokines play an important role in the orchestration of the antibody response. Several previous studies have attempted to identify distinct cytokines responsible for the inflammatory changes and different manifestations of CVID, but there are conflicting results regarding the cytokine profiles in CVID patients. In light of this, an extensive review regarding the level of various cytokines and their potential therapeutic role in CVID patients was performed. This review delineates the contribution of interleukin (IL)-1, IL-2, IL-4, IL-5, IL-6, IL-7, IL-10, IL-12, IL-21, interferons, tumor necrosis factor (TNF)-α, IL-17, APRIL (a proliferation inducing ligand) and BAFF (B cell activating factor) in CVID disease and outline their potential therapeutic implications in these patients.

Defective T-cell activation caused by impairment of the TNF receptor 2 costimulatory pathway in common variable immunodeficiency

BACKGROUND

Patients with common variable immunodeficiency have defective T-cell activation after stimulation via T-cell receptor (TCR)/CD28 or by recall antigens.

OBJECTIVE

In the current study, we investigated whether TNF-receptor 2 (RII) costimulation, which is important for sufficient TCR/CD28 stimulation, was significantly impaired in common variable immunodeficiency (CVID).

METHODS

We studied T-cell activation events such as CD69 induction, calcium flux through store operated calcium channels, protein kinase C-theta translocation, and costimulation via TNF-RII compared with costimulation via CD28.

RESULTS

By measuring TNF receptor-associated factor 1 expression, which is induced by TCR alone and can be upregulated by either CD28 or TNF-RII costimulation, we show that costimulation via CD28 is intact, whereas costimulation via TNF-RII in these patients is impaired. The ras-activation pathway as tested by CD69 induction, calcium flux through store operated calcium channels, and protein kinase C-theta translocation were comparable in CVID and control T cells.

CONCLUSION

Taken together, these data indicate that the primary TCR signal as well as the signal derived from CD28 are normal but that TNF-RII-supported TCR costimulation is defective, most likely leading to impairment of an important amplification loop, such as TNF-RII augmented nuclear factor-kappaB activation.

CLINICAL IMPLICATIONS

The finding of defective TNF-RII cosignaling in patients with CVID may help to define the activation pathway affected, thus potentially leading to a characterization of the molecular defect and molecular diagnosis in at least some of these patients.

T and B lymphocyte subpopulations and activation/differentiation markers in patients with selective IgA deficiency

Selective deficiency of immunoglobulin A (IgAD) and common variable immunodeficiency (CVID) are genetically closely related diseases, both of unknown pathogenesis. A plethora of abnormalities in lymphocyte subpopulations and expression of activation markers were repeatedly documented in CVID patients, while almost no data are available about lymphocyte subpopulations in IgAD patients. We determined basic lymphocyte subpopulations and those subpopulations that were reported to be abnormal in CVID patients (CD25, human leucocyte antigen (HLA)-DR CD45RA, CD45RO, CD27, CD28 and CD29 on both CD4(+) and CD8(+) cells, CD57 and CD38 on CD8(+) cells, CD21, CD27, IgM, IgD on B lymphocytes) in 85 patients with IgAD, 47 patients with CVID and in 65 healthy controls. Statistical analysis was performed by the Mann-Whitney U-test; significant P-values were determined by means of Bonferoni's correction. Our results showed an increase in the relative number of CD8(+) cells and a decrease in the absolute number of CD4(+) cells compared to healthy people, but similar abnormalities in CVID patients were much more expressed. IgAD patients had significantly decreased expression of HLA-DR and increased expression of CD25 on CD4(+) lymphocytes, also CD29 expression was decreased on CD8(+) cells, while other activation/differentiation markers on T cells (including the expression of CD45RA and CD45RO antigens) were not changed. There were no statistically significant abnormalities in B lymphocyte developmental stages in IgAD patients compared to healthy controls. Our observation showed that the majority of T and B lymphocyte subpopulation abnormalities described previously in CVID are not present in IgAD patients.

Age dependency and mutual relations in T and B lymphocyte abnormalities in common variable immunodeficiency patients

Common variable immunodeficiency (CVID) is primary hypogammaglobulinaemia with an unknown aetiopathogenesis. Although various abnormalities of T and B cells have been described, their pathogenetic roles are unclear. We determined T and B lymphocyte subsets known to be abnormal in CVID in order to disclose possible relations between numerical abnormalities in those cells. Markers associated with B cell development (CD21, CD27, IgM, IgD) were determined on B lymphocytes (CD19+); T lymphocyte development (CD45RA, CD45RO, CD62L) and activation markers (CD25, CD27, CD28, CD29, CD38, CD57, HLA-DR) were determined on CD4+ and CD8+ T lymphocytes in 42 CVID patients and in 33 healthy controls. Abnormalities in CD4+ T lymphocyte activation markers (increase in CD29, HLA-DR, CD45RO, decrease in CD27, CD62L, CD45RA) were observed particularly in patients with a decreased number of memory (CD27+) and mature (CD21+) B cells (group Ia according to the Freiburg group's classification), while abnormalities observed in CD8+ cells (increase in CD27 and CD28 and decrease in HLA-DR, CD57 and CD38) did not depend upon grouping patients together according to B lymphocyte developmental subpopulations. We observed correlations between immature B cells (IgM+ CD21-) and expression of CD27, CD62L, CD45RA, CD45RO and HLA-DR on CD4+ T cells in CVID patients but not in the control group. The expression of CD27 and CD45RA on CD4+ T lymphocytes, such as the percentage of IgD+ CD27- and IgD+ CD27+ cells in B lymphocytes, showed age dependency to be more significant than in the control group. Our study demonstrates that T and B lymphocyte abnormalities in CVID are partially related to each other. Some of those abnormalities are not definite, but may evolve with age of the patient.

Defective Vav expression and impaired F-actin reorganization in a subset of patients with common variable immunodeficiency characterized by T-cell defects

Common variable immunodeficiency (CVID) is a primary immune disorder characterized by impaired antibody production, which is in many instances secondary to defective T-cell function (T-CVID). We have previously identified a subset of patients with T-CVID characterized by defective T-cell receptor (TCR)-dependent protein tyrosine phosphorylation. In these patients, ZAP-70 fails to be recruited to the TCR as the result of impaired CD3zeta phosphorylation, which is, however, not dependent on defective Lck expression or activity. Here we show that neither Fyn nor CD45 is affected in these patients. On the other hand, T-CVID T cells show dramatic defects in the Vav/Rac pathway controlling F-actin dynamics. A significant deficiency in Vav protein was indeed observed; in 3 of 4 patients with T-CVID, it was associated with reduced VAV1 mRNA levels. The impairment in Vav expression correlated with defective F-actin reorganization in response to TCR/CD28 co-engagement. Furthermore, TCR/CD28-dependent up-regulation of lipid rafts at the cell surface, which requires F-actin dynamics, was impaired in these patients. The actin cytoskeleton defect could be reversed by reconstitution of Vav1 expression in the patients' T cells. Results demonstrate an essential role of Vav in human T cells and strongly suggest Vav insufficiency in T-CVID.

Exogenous leptin restores in vitro T cell proliferation and cytokine synthesis in patients with common variable immunodeficiency syndrome

Common variable immunodeficiency (CVID) is a primary immunodeficiency characterized by hypogammaglobulinemia. Leptin has been implicated as an antiapoptotic compound as well as a stimulant of the immune response. Leptin administration is capable of reversing the immune deficiency that occurs upon starvation. We investigated a possible role for leptin in CVID; a condition associated with lowered plasma leptin levels. Thirty-eight patients were studied. Addition of leptin to the tissue culture media of PBMC from CVID patients increased the proliferative response of lymphocytes to mitogens and decreased activation-induced apoptosis of these cells. IL-2 and specially IL-4 production also increased significantly upon addition of leptin to the PBMC cultures. Our results suggest that leptin may be involved in some of the cellular defects observed in CVID and indicate a novel therapeutic strategy to improve immune function in these patients.

Regulation of TCR-mediated T cell activation by TNF-RII

In the present study, we investigated the role of tumor necrosis factor receptor II (TNF-RII) in human T cell activation induced via the T cell receptor (TCR) in an antigen-presenting cell-independent system. Our results confirm that interaction of TNF-alpha with TNF-RII but not TNF-RI is directly costimulatory to TCR-mediated T cell activation, thereby augmenting T cell proliferation, expression of T cell activation markers (CD25, human leukocyte antigen-DR, TNF-RII), and secretion of cytokines such as interferon-gamma and TNF-alpha. In contrast to the well-defined costimulatory molecule CD28, costimulation via TNF-RII showed significant differences in kinetics, requirement for cross-linking, redundancy of intracellular signaling pathways involved, and the capacity to induce interleukin (IL)-2, IL-10, and IL-13 secretion. In addition, cross-linking TNF-RII had the capacity to down-regulate TCR/CD28-induced Ca++ mobilization, IL-2 mRNA expression, and IL-2 and IL-10 secretion. Taken together, our findings demonstrate that TNF-RII plays a unique role among the T cell costimulatory molecules, as TNF-RII ligation can have positive and negative effects on TCR-dependent signaling. TNF-RII cross-linking has an inhibitory effect on early TCR signaling events proximal to induction of Ca++ flux, which ultimately leads to modulation of the T cell cytokine pattern expressed.

Three novel mutations reflect the variety of defects causing phenotypically diverse X-linked hyper-IgM syndrome

X-linked hyper-IgM syndrome (HIGM1) (MIM musical sharp 308230), is a severe primary immunodeficiency caused by mutations in the gene coding for CD40 ligand (CD40L or CD154), a member of the tumour necrosis factor (TNF) superfamily. The interaction of this protein with its ligand, CD40, mediates crucial processes in the immune response. The variety of defects that have been described in HIGM1 patients range from a complete lack of CD40L protein expression to missense mutations that interfere with its interaction with CD40L. In this study we describe three families - a total of seven HIGM1 patients and carriers, presenting a spectrum of severity in clinical evolution. In two of these families, patient DNA samples were available for genetic studies. In the third, carrier detection was performed on female family members. The results of immunological studies - the different patterns of CD40L expression and binding capacity as measured by flow cytometry - and molecular diagnosis are presented. Three novel mutations were identified: an intron mutation that partially interferes with the splicing process (intron 3, position + 5 G/T); a missense mutation (Ser222 Phe) located in the molecular region which interacts with the receptor and which abrogates binding capacity; and a 14 base pair deletion leading to a frameshift and a premature truncated mutation (del I 171 X 195). An attempt to correlate protein expression and function of the CD40L mutants with clinical disease evolution is described.

Linkage of autosomal dominant common variable immunodeficiency to chromosome 5p and evidence for locus heterogeneity

Common variable immunodeficiency (CVID, OMIM 240500) and selective immunoglobulin A deficiency (IgAD) are the most frequent primary immunodeficiencies in humans. Of the cases with CVID/IgAD, 20%-25% are familial, but the only previous claims of linkage or association are to the HLA region on chromosome 6p. We report the results of a genome-wide scan in three multiplex families with CVID, IgAD, and dysgammaglobulinemia, where affection is inherited in an autosomal dominant pattern. Two of the families are consistent with linkage to the telomeric region of chromosome 5p, whereas the third is consistent with linkage to the HLA region. Using a locus heterogeneity model and a conservative penetrance model, we obtained a LOD score of 3.35 for the 5p region. We sequenced the exons of one promising candidate gene within this region (PDCD6, also known as ALG-2) but found no causative mutation.

Homozygous loss of ICOS is associated with adult-onset common variable immunodeficiency

No genetic defect is known to cause common variable immunodeficiency (CVID), a heterogeneous human disorder leading to adult-onset panhypogammaglobulinemia. In a search for CVID candidate proteins, we found four of 32 patients to lack ICOS, the "inducible costimulator" on activated T cells, due to an inherited homozygous deletion in the ICOS gene. T cells from these individuals were normal with regard to subset distribution, activation, cytokine production and proliferation. In contrast, naive, switched and memory B cells were reduced. The phenotype of human ICOS deficiency, which differs in key aspects from that of the ICOS-/- mouse, suggests a critical involvement of ICOS in T cell help for late B cell differentiation, class-switching and memory B cell generation.

Assessment of thymic output in common variable immunodeficiency patients by evaluation of T cell receptor excision circles

Common variable immunodeficiency (CVID) is a heterogeneous syndrome characterized by repeated infections and hypogammaglobulinaemia. Additionally, T-cell abnormalities including lymphopenia, decreased proliferation to mitogens and antigens, and the reduced production and expression of cytokines, have also been observed. In this study we have investigated the expression of naive, memory and activation markers in T-cell subpopulations in 17 CVID patients in comparison to age-matched normal controls. The numbers of CD4+ T cells, including CD45RA+CD62L+ and, to a lesser extent, CD45RA-CD62L+/RA+CD62L- were significantly reduced in patients, whereas CD8+ T cells were within normal range. In contrast, HLA-DR+ cells were increased both in CD4+ and CD8+ T cells. To assess the thymic output, we analysed the presence of T-cell receptor excision circles (TRECs) in CD4+ and CD8+ T cells by quantitative PCR. TRECs were decreased significantly in patients and the rate of TREC loss was higher with increasing age. TRECs correlated with naive CD4+ T cells, whereas there was an inverse relationship between TRECs and CD8+HLA-DR+ and CD8+CD45RA-CD62L+/RA+CD62L- T cells. Our results suggest the presence of a defect in the naive T cell compartment with origin at the thymic level in CVID, and indicate that TREC may be a useful marker to monitor thymic function in this primary immunodeficiency.

Impaired up-regulation of CD70 and CD86 in naive (CD27-) B cells from patients with common variable immunodeficiency (CVID)

CVID is characterized by reduced serum levels of all switched immunoglobulin isotypes (IgG, IgA, IgE) predisposing patients to recurrent infections of their respiratory and gastrointestinal tract. Correspondingly, most CVID patients exhibit a severely decreased proportion of class switched memory B cells (CD19+CD27+IgD-IgM-IgG+ or IgA+) in their peripheral blood (CVID type I). We previously identified a subgroup of CVID patients showing a significantly reduced expression of CD86 and CD137 following activation in vitro of PBMC or purified B cells (CD19+) with anti-IgM plus IL-2. Here we extend our previous studies by asking whether highly purified, cell-sorted naive B cells show already an expression defect of B cell surface molecules relevant in activation (CD39, CD69), differentiation (CD24, CD27, CD38) or T-B interaction (CD25, CD70, CD86). We stimulated cell-sorted, naive B cells (CD19+CD27-IgM+IgDhighIgG-IgA-) from 10 CVID patients and 10 healthy controls for 4 days with anti-IgM plus IL-2 in the absence or presence of autologous CD4+ T cells and measured the expression of the referred surface molecules. Based on reduced or normal numbers of switched memory B cells the CVID patients had previously been classified into eight type I patients and two type II patients, respectively. Interestingly, only the molecules CD25, CD70 and CD86, all relevant in cognate T-B interaction, showed a significantly lower expression in naive B cells from CVID patients compared to controls. While coculture with autologous CD4+ T cells normalized the CD25 expression, CD70 and CD86 expression remained subnormal, notably in the eight CVID patients of type I. These findings strongly suggest an intrinsic signalling or expression defect for CD70/CD86 at the level of naive B cells in type I CVID patients.

Residual expression of functional MHC class II molecules in twin brothers with MHC class II deficiency is cell type specific

We examined major histocompatibility complex (MHC) class II expression in B cells, peripheral blood monocytes, activated T cells, epidermal Langerhans cells, monocyte-derived dendritic cells, dermal microvascular endothelial cells (DMEC) and fibroblasts of twin brothers with MHC class II deficiency. Although residual human leucocyte antigen (HLA)-DR expression was found on a subpopulation of epidermal Langerhans cells and a subset of peripheral blood monocyte-derived dendritic cells, the patients' B cells, monocytes and activated T cells were HLA-DR negative. After treatment with interferon-gamma (IFN-gamma), the patients' DMEC expressed HLA-DR but not -DP and -DQ at the protein and mRNA level, whereas IFN-gamma failed to induce HLA-DR expression on dermal fibroblasts. The patients' monocyte-derived dendritic cells were capable of processing and presenting tetanus toxoid to autologous T cells, and patient-derived DMEC induced the proliferation of allogeneic CD4(+) T cells in an MHC class II-restricted fashion, indicating that the observed residual MHC class II surface expression was functional. The findings reported show that the defect encountered in these patients is not necessarily expressed to the same extent in different cell lineages, which is relevant for the understanding of the patients' phenotype and also illustrates that only small amounts of MHC class II are needed to mount a functional cellular immune response in vivo.

Defective surface expression of attractin on T cells in patients with common variable immunodeficiency (CVID)

The proliferative responses of T lymphocytes of a subset of patients with CVID are abnormally low. This may be due to abnormalities in extracellular interactions or signalling defects downstream from membrane-associated receptors. Demonstrating that the T cell receptor signalling was normal, we observed no abnormal pattern of activation-induced tyrosine phosphorylation in cells from CVID patients. Moreover, the addition of exogenous IL-2 increased the low proliferation to mitogens, thus indicating the integrity of the IL-2R signalling apparatus. Attractin is a rapidly expressed T cell activation antigen involved in forming an association between T cells and monocytes. Twenty-four to 48 h after activation by CD3 cross-linking, attractin expression was not up-regulated on the cells of CVID patients despite normal up-regulation of CD25 and CD26. On control cells, however, attractin expression was up-regulated together with CD25 and CD26. The addition of the purified 175-kD attractin was capable of restoring the proliferative response of peripheral blood mononuclear cells following CD3 X-L in the presence of suboptimal concentrations of rIL-2 (10 and 20 U/ml). The effect was dose-dependent with the maximal effect at a concentration of 500 ng/ml, and present at a concentration as low as 50 ng/ml. Due to the likely role of attractin in cell guidance and amplification of the immune response, our results indicate that the lack of up-regulation of the molecule in patients with CVID may in turn affect any further step of productive immune response. Our finding may also imply a potential therapeutic role for this novel molecule.

Characterization of the T cell receptor repertoire in patients with common variable immunodeficiency: oligoclonal expansion of CD8(+) T cells

Common variable immunodeficiency is characterized by an impairment in antibody production of at least two immunoglobulin isotypes, and abnormalities of both B and T cells have also been described. In this study, a profound alteration of the T cell receptor repertoire was noted, especially in CD8(+) T cells, in CVID patients when compared to a control group. However, the higher number of oligoclonally expanded populations seen in the patient group was not dependent on age, whereas in the control group an age-related accumulation of these populations was noted. Expansion of CD8(+) CD28(-) T cells in these patients is strongly correlated with T cell receptor repertoire restriction. Furthermore, analysis of cytokine production showed a statistically significant increase in IFN-gamma secretion in the patient group. Lastly, CD94 and perforin were expressed at increased frequencies on CD8(+) T cells in the patient group when compared to the control group. We speculate that these findings support the concept that CD8(+) T cells may play an important regulatory role in CVID.

Enhanced apoptosis of T cells in common variable immunodeficiency (CVID): role of defective CD28 co-stimulation

CVID is a primary immune disorder in which hypogammaglobulinaemia may be associated with a number of T cell defects including lymphopenia, anergy, impaired lymphocyte proliferation and deficient cytokine secretion. In this study we show that T cells of CVID subjects, in comparison with control T cells, undergo spontaneous apoptosis in culture and markedly accelerated apoptosis after gamma-irradiation. Although costimulation of the CD28 receptor following engagement of the TCR/CD3 receptor normally provides a second signal necessary for IL-2 secretion, CD28 costimulation in CVID does not significantly increase IL-2 production, nor does this combination of activators enhance the survival of irradiated CVID T cells, as it does for cultured normal T cells. Addition of IL-2 enhances CVID T cell survival, suggesting that the IL-2 signalling pathways are normal. CVID T cells have similar expression of Bcl-2 to control T cells. CD3 stimulation up-regulates T cell expression of bcl-xL mRNA for normal T cells, but anti-CD28 does not augment bcl-xL expression for CVID subjects with accelerated apoptosis. Defects of the CD28 receptor pathway, leading to cytokine deprivation and dysregulation of bcl-xL, could lead to poor T cell viability and some of the cellular defects observed in CVID.

Mitogen-induced T-cell CD69 expression is a less sensitive measure of T-cell function than [(3)H]-thymidine uptake

The most widely used in vitro measure of T-cell function has been the assessment of mitogen induced proliferation by [(3)H]-thymidine incorporation. Mitogens also induce T-cell surface expression of a number of molecules associated with activation, including CD69. Recent reports have suggested that flow cytometric analysis of CD69 expression may be a simpler and faster means of measuring T-cell function. Most studies have been on normal subjects, and the sensitivity of CD69 expression as an in vitro measure of clinical immunodeficiency remains unknown. We address this issue by concurrently measuring mitogen-stimulated T-cell CD69 expression and [(3)H]-thymidine incorporation in a normal population and five immunocompromised patients negative for the human immunodeficiency virus (HIV). All patients had recurrent infections and had known causes of immunodeficiency. Whole blood cultures were setup to measure phytohaemagglutinin A (PHA)- and superantigen staphylococcal enterotoxin B (SEB)-induced CD69 expression at 5, 24, and 72 h, and [(3)H]-thymidine incorporation at 72 h. All immunodeficient patients had lower than normal PHA responses and 3 of 4 had low SEB responses. However in 7 out of 8 of the patient tests, mitogen-induced T-cell CD69 expression was within the normal range. Similar results were found with CD4(+) T-cell CD69 expression. This study indicates that measurement of mitogen-induced T-cell CD69 expression lacks sensitivity in determining T-cell dysfunction in HIV-negative immunodeficient patients.

Long-term decrease of CD4+CD45RA+ T cells and impaired primary immune response after post-traumatic splenectomy

Congenital or acquired absence of the spleen and functional hyposplenism are associated with abnormalities of host defence such as an increased susceptibility to infection with encapsulated bacteria. The effects of the lack of the spleen on cell-mediated immunity are largely unknown. In the present study we have investigated peripheral blood lymphocyte subpopulations in healthy adults who had undergone splenectomy because of severe abdominal trauma > 4 years before the study. The results show a significant reduction in the percentage of CD4+ T cells due to a selective and long-term decrease in the percentage of CD4+CD45RA+ lymphocytes, the CD4+ T-cell subset mainly involved in primary immune responses to newly encountered antigens. Levels of the reciprocal CD45RO+CD4+ T-cell subset were comparable between splenectomized and control individuals, as were lymphoproliferative responses and IFN-gamma production to recall antigens. Decreased levels of CD4+CD45RA+ cells were accompanied by an impairment in primary immune responsiveness, as assessed by investigating T-cell proliferation to stimulation with keyhole limpet haemocyanin and by measuring antibody responses following primary immunization with a clinically relevant T-dependent antigen, hepatitis A vaccine, in vivo. These findings suggest a possible role of the spleen in the generation, maintenance and/or differentiation of naive, unprimed T cells or their precursors, which might have a possible functional relevance for primary immune responses following splenectomy.

The genetic basis for the association of the 8.1 ancestral haplotype (A1, B8, DR3) with multiple immunopathological diseases

An individual's major histocompatibility complex (MHC) ancestral haplotype (AH) is the clearest single determinant of susceptibility to MHC associated immunopathological disease, as it defines the alleles carried at all loci in the MHC. However, the direct effects of any of the 150-200 genes that constitute the MHC are difficult to determine since recombination only occurs at defined hotspots. This review concerns the 8.1 AH (HLA-A1, C7, B8, C4AQ0, C4B1, DR3, DQ2), which is carried by most Caucasians with HLA-B8. It is associated with accelerated human immunodeficiency virus (HIV) disease, and susceptibility to insulin-dependent diabetes mellitus (IDDM), systemic lupus erythematosus, dermatitis herpetiformis, common variable immunodeficiency and IgA deficiency, myasthenia gravis and several other conditions. We have mapped susceptibility genes for HIV, IDDM and myasthenia gravis to the central MHC between HLA-B and the tumour necrosis factor or complement genes. Here we consider which of the remaining 8.1-associated diseases are more closely associated with HLA-DR3 and/or DQ2. Several candidate genes in the central MHC have the potential to modulate immune or inflammatory responses in an antigen-independent manner, as is seen in studies of cultured cells from healthy carriers of the 8.1 AH. Hence these genes may act as a common co-factor in the diverse immunopathological conditions associated with the 8.1 AH.