Defective CD2 T cell pathway activation in common variable immunodeficiency (CVID)

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.

Age-related impairment of T cell proliferative responses related to the decline of CD28+ T cell subsets

The impairment of phytohaemagglutinin-triggered lymphocyte proliferation represents a prominent immunologic abnormality in elderly individuals. To assess whether the reduced function is related to a CD28/B7 signalling deficiency, purified T lymphocytes and antigen presenting cells (APCs) were analyzed for their phenotypic profile and/or functional capacities. T cell responses to immobilized OKT3 monoclonal antibodies (mAb) or a combination of anti-CD2 mAb and phorbol esters were unaffected in old subjects when compared to the younger counterpart. In contrast, CD28 costimulation in the presence of OKT3 or anti-CD2 mAb, gave rise to significantly diminished T cell proliferative responses. These findings correlated with a marked decline of CD28(+) T cell frequency, which mainly involved the CD4(-)CD45RO(-) cell subset. The defect in CD28 expression could not be reversed by T cell stimulation, as a comparable increase in CD28 levels occurred in both 'aged' and 'young' T cells after in vitro activation. Moreover, the elderly group did not exhibit a reduction of interleukin (IL)-2 synthesis, as assessed at 24 h of culture, regardless of the stimulant used. Finally, B7.2 (CD86) expression by 'aged' CD14(+) APCs was unaffected in both resting and interferon-gamma activated cells. These results suggest that an intrinsic defect in CD28 expression might in part account for the age-related decline of T cell proliferative responses.

Deficiency of somatic hypermutation of immunoglobulin G transcripts is a better predictor of severe respiratory tract infections than lack of memory B cells in common variable immunodeficiency

Defects of memory B cells and of somatic hypermutation (SHM) are involved in the pathogenesis of common variable immunodeficiency (CVID). Here we report for the first time a systematic study of the relationship between memory B cell deficiency and SHM abnormalities in CVID, and relate these variables to prediagnostic infections. Isotype switched Vh3-23 transcripts were undetectable or low in 30% (IgG) and 63% (IgA) of the patients, but never in controls (P < 0.001). When measurable, the SHM fraction of transcripts was significantly lower in patients (IgM: median 32% vs. 56% (P = 0.0002); IgG: 72% vs. 87% (P = 0.0002); IgA: 81% vs. 88% (P = 0.04)). The concentration of switched (CD19+/CD27+/IgG+) and unswitched (CD19+/CD27+/IgM+/IgD+) memory cells was reduced in 75% and 58% of the patients, respectively. Patients with reduced concentrations of switched memory B cells had normal or low SHM, and only the IgG SHM fraction correlated with prediagnostic incidence of severe respiratory tract infections (P = 0.004).

Deficiency of somatic hypermutation of the antibody light chain is associated with increased frequency of severe respiratory tract infection in common variable immunodeficiency

Reduced levels of somatic hypermutation (SHM) have recently been described in IgG-switched immunoglobulin genes in a minority of patients with common variable immunodeficiency (CVID), demonstrating a disruption of the normal linkage between isotype switch and SHM. To see if, irrespective of isotype, there is a tendency to use unmutated immunoglobulin genes in CVID, we studied SHM in kappa light-chain transcripts using a VkappaA27-specific restriction enzyme-based hot-spot mutation assay (IgkappaREHMA). Hot-spot mutations were found in 48% (median; reference interval, 28%-62%) of transcripts from 53 healthy controls. Values were significantly lower in 31 patients (median, 7.5%; range, 0%-73%; P < .0000001) of whom 24 (77%) had levels below the reference interval. Low levels of SHM correlated with increased frequency of severe respiratory tract infection (SRTI; P < .005), but not with diarrhea (P = .8). Mannose-binding lectin (MBL) deficiency also correlated with SRTI score (P = .009). However, the correlation of SHM and SRTI was also seen when only patients with normal MBL genotypes were analyzed (n = 18, P = .006). A slight decline of mutated fractions over years was noted (P = .01). This suggests that most patients with CVID fail to recruit affinity-maturated B cells, adding a qualitative deficiency to the quantitative deficiency characterizing these patients.

Therapeutic strategies in common variable immunodeficiency

The treatment of common variable immunodeficiency (CVID) is currently based on the early recognition of the condition and replacement immunoglobulin combined with prompt treatment of infections and complications. The route of administration, dose and frequency of administration of immunoglobulin still vary between centres and countries. Other interventions aimed at overcoming the immunological defects in CVID such as interleukin-2 therapy are being studied but there is as yet insufficient evidence to support their routine use. The treatment of complications such as suppurative lung disease uses principles broadly similar to those used for cystic fibrosis, whereas the granulomatous complications involving the lungs and other organ systems are in need of much more research to define optimum therapies.

CD4+ cells from patients with Common Variable Immunodeficiency have a reduced ability of CD40 ligand membrane expression after in vitro stimulation

BACKGROUND

Common Variable Immunodeficiency (CVID) is characterized by defective antibody production. This has been variably attributed to intrinsic B-cell defects or to T-cell disfunctions. Recently, it has been reported that the expression of the CD40 Ligand (CD40L), a T-cell surface molecule that plays a critical role in the cell-contact-mediated helper signals provided to B-cells, is defective in a subset of patients with CVID.

METHODS

To demonstrate that the defective expression is due to intrinsic functional abnormalities of CD4+ lymphocytes, CD4+ cells were purified from eight patients with CVID and eight age-paired controls, stimulated with PMA+Ionomycin, and studied for CD40L expression by flow cytometry using specific monoclonal antibodies.

RESULTS AND CONCLUSIONS

The percentage of CD4+ cells expressing CD40L after optimal stimulation was correlated with age both in patients with CVID (r: 0.74; p: 0.04) and in healthy controls (r: 0.73; p: 0.04). The percentage of CD40L+ cells was reduced in patients with CVID compared to that of controls (p: 0.02 when data are paired for age) with a reduced density of expression (p: < 0.01). The defect was variable in different patients and in some cases it was marginal.

Adult immunodeficiency and rheumatic disease

Several rheumatic illnesses may develop in adults with primary or acquired immunologic defects. Individuals with primary defects in B-cell antibody production, such as common variable immunodeficiency of selective IgA deficiency, and those with defects of complement components, have an increased prevalence of systemic lupus erythematosus--like syndromes or other autoimmune diseases. Defects in immunoglobulin production may be complicated by inflammatory or infectious arthritis. Infection with HIV-1 may be associated with diverse rheumatic conditions, including diffuse infiltrative lymphocytosis syndrome, myopathies, vasculitides, inflammatory arthritides, and infectious musculoskeletal complications. An approach to these disorders that takes into consideration the underlying mechanism of disease is presented. Appropriate strategies aimed at treatment of the underlying immunodeficiency may improve the clinical course of the associated rheumatic disorder.

Defective functional response to membrane stimuli in lymphocytes from patients with benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a local disturbance in the prostate that may involve an inflammatory infiltrate predominantly composed of activated lymphocytes and macrophages. The activation and proliferative response of T lymphocytes to different mitogenic signals has been analysed in peripheral blood mononuclear cells (PBMC) from 45 patients with BPH and 55 healthy controls. The PBMC obtained from the patients showed a significant specific impairment in proliferation, CD25 expression and IL-2 production in response to stimulation with lectins (phytohaemagglutinin (PHA), concanavalin A (Con A)), that was not corrected by the addition of IL-2 or of phorbol esters (phorbol myristate acetate (PMA)). Also, the CD28 response was defective in patient PBMC. Activation with anti-CD3 or anti-CD2 MoAbs was normal, but the addition of PMA to these stimuli provoked a significant defective response. Only the use of transmembrane stimuli (PMA and ionomycin) elicited responses similar to those found in the control group. The results indicate that peripheral T lymphocytes from BPH patients show a functional impairment that is mainly explained by an alteration of membrane signals (PHA, CD28) and is distal to protein kinase C (PKC) activation.