Intravenous immunoglobulin replacement induces an in vivo reduction of inflammatory monocytes and retains the monocyte ability to respond to bacterial stimulation in patients with common variable immunodeficiencies

• In CVID patients, IgG administered at replacement dosages cause a reduction of circulating monocytes.
• IVIgs exert an in vivo anti-inflammatory effect by reducing the frequency of intermediate pro-inflammatory monocytes.
• IVIgs infusion reduce the expression of adhesion molecules CD11b and Siglec 9 on classical monocytes.
• After IVIgs, monocytes’ ability to respond to E. coli stimulation, in terms of CD11b and Siglec 9 expression, is preserved.
• Monocytes’ oxidative burst decrease after IVIg infusion, but remains comparable to that observed in HD.

Intravenous IgG administration induces significant modifications in the innate and adaptive compartment of the immune system including the monocyte/macrophage system. We analyzed the in vivo effect of IgG administered at replacement dosages on the frequency of monocytes subsets, on the modulation of CD11b and sialic acid-binding immunoglobulin-like lectin receptor (Siglec 9) expression and on monocytes production of reactive oxygen species. We showed that patients with Common Variable Immune Deficiency have an increased frequency pro-inflammatory intermediate CD14++CD16+ monocytes and an increased expression of CD11b and Siglec 9 on monocytes. IgG administered at replacement dosages exerted an in vivo anti-inflammatory effect as shown by a reduction of circulating monocytes, of intermediate pro-inflammatory monocytes, of CD11b and Siglec 9 expression and of ex vivo monocytes oxidative burst. Nevertheless, intravenous IgG administration did not affect the monocyte functional ability to respond to a bacterial stimulation in terms of CD11b and Siglec 9 expression and reactive oxygen species production.