Monocyte activation is a feature of common variable immunodeficiency irrespective of plasma lipopolysaccharide levels

Abstract

Common variable immunodeficiency disorders (CVID), the most frequent cause of symptomatic primary immunodeficiency, are defined by impaired antibody production. Notwithstanding, T cell activation and granulomatous manifestations represent the main causes of CVID morbidity even in patients receiving immunoglobulin (Ig) G replacement therapy. Additionally, gut pathology is a frequent feature of CVID. In this study, we investigated monocyte imbalances and their possible relationship with increased microbial translocation in CVID patients. Monocyte subsets were defined according to CD14 and CD16 expression levels and evaluated in terms of human leucocyte antigen D-related (HLA-DR), CD86 and programmed death-1 molecule ligand 1 (PD-L1) expression by flow cytometry, in parallel with the quantification of plasma lipopolysaccharide (LPS) and serum levels of soluble CD14 (sCD14), LPS-binding protein (LBP) and anti-LPS antibodies. CVID patients (n=31) featured significantly increased levels of serum sCD14 and an expansion of CD14(bright) CD16(+) monocytes in direct correlation with T cell and B cell activation, the latter illustrated by the frequency of the CD21(low) CD38(low) subset. Such alterations were not observed in patients lacking B cells due to congenital agammaglobulinaemia (n=4). Moreover, we found no significant increase in circulating LPS or LBP levels in CVID patients, together with a relative preservation of serum anti-LPS antibodies, in agreement with their presence in commercial IgG preparations. In conclusion, CVID was associated with monocyte imbalances that correlated directly with T cell activation markers and with B cell imbalances, without an association with plasma LPS levels. The heightened monocyte activated state observed in CVID may represent an important target for complementary therapeutic strategies.

Fig. 1

Monocyte activation markers in common variable immunodeficiency (CVID) and congenital agammaglobulinaemia. (a) Serum levels of soluble CD14 (sCD14). Each dot represents one individual, with bars indicating mean values. Open circles refer to healthy individuals, solid circles to CVID patients, and grey squares to congenital agammaglobulinaemia (Agamma) patients. (b) Illustrative flow cytometric analysis of monocyte subsets according to CD14 and CD16 expression levels in representative CVID (right panel) and healthy (left panel) individuals. (c) Frequency and absolute counts of monocyte subsets as defined in (b). (d) Mean fluorescence intensity (MFI) of human leucocyte antigen D-related (HLA-DR), CD86 and programmed death-1 molecule ligand 1 (PD-L1) within total monocytes. Healthy individuals are represented in open bars, CVID patients in solid bars and congenital agammaglobulinaemia patients in grey bars. Bars indicate mean ± standard error of the mean. P-values of statistically significant differences are shown.

Fig. 2

Plasma lipopolysaccharide (LPS) levels and related molecules in common variable immunodeficiency (CVID). (a) Plasma LPS levels. (b) Serum LPS-binding protein (LBP) levels. (c) Anti-LPS antibodies (left) and its ratio relative to total immunoglobulin (Ig) G (right). Each dot represents one individual: healthy individuals are represented in open circles, CVID patients in solid circles. Bars indicate mean. P-values of statistically significant differences are shown.

Fig. 3

Relationship between markers of monocyte and T cell activation in common variable immunodeficiency (CVID). Correlation between the frequency of CD14^brightCD16⁺ monocytes and the frequency of naive (CD45RA⁺CD27⁺, left panel), activated human leucocyte antigen D-related (HLA-DR)⁺CD38⁺ (middle panel) or interferon (IFN)-γ-producing cells (right panel) within CD4 T cells in CVID patients (solid circles) and in healthy individuals (open circles). Each dot represents one individual. Spearman's correlation coefficients are shown.

Fig. 4

Markers of monocyte activation in common variable immunodeficiency (CVID) grouped according to the EuroClass classification. (a) Mean fluorescence intensity (MFI) of programmed death-1 molecule ligand 1 (PD-L1) within CD14^brightCD16⁺ monocytes. Healthy individuals are represented in open bars and CVID patients in solid bars. (b) Frequency of CD14^brightCD16⁺ monocytes. Bars indicate mean ± standard error of the mean. P-values of statistically significant differences are shown. (c) Correlation between the frequency of CD14^brightCD16⁺ monocytes and the frequency of CD21^lowCD38^low B cells in CVID patients (solid circles) and in healthy individuals (open circles). Each dot represents one individual. Spearman's correlation coefficients are shown.