Intravenous immunoglobulins suppress T-cell priming by modulating the bidirectional interaction between dendritic cells and natural killer cells

The modes of action of intravenous immunoglobulins (IVIgs) in exerting their immunomodulatory properties are broad and not fully understood. IVIgs can modulate the function of various immune cells, including suppressing the capacity of dendritic cells (DCs) to stimulate T cells. In the present study, we showed that DCs matured in the presence of IVIgs (IVIg-DCs) activated NK cells, and increased their interferon-γ production and degranulation. The activated NK cells induced apoptosis of the majority of IVIg-DCs. In consequence, only in the presence of NK cells, IVIg-DCs were 4-fold impaired in their T-cell priming capacity. This was due to NK-cell-mediated antibody-dependent cellular cytotoxicity (ADCC) to IVIg-DCs, probably induced by IgG multimers, which could be abrogated by blockade of CD16 on NK cells. Furthermore, IVIg-DCs downregulated the expression of NKp30 and KIR receptors, and induced the generation of CD56^brightCD16^-CCR7 ⁺ lymph node-type NK cells. Our results identify a novel pathway, in which IVIgs induce ADCC of mature DCs by NK cells, which down-sizes the antigen-presenting pool and inhibits T-cell priming. By influencing the interaction between DCs and NK cells, IVIgs modulate the ability of the innate immunity to trigger T-cell activation, a mechanism that can "cool down" the immune system at times of activation.