CD1d-restricted invariant Natural Killer T (iNKT) cells are unconventional innate-like T cells whose functions highly depend on the interactions they establish with other immune cells. Although extensive studies have been reported on the communication between iNKT cells and macrophages in mice, less data is available regarding the relevance of this crosstalk in humans. Here, we dove into the human macrophage-iNKT cell axis by exploring how iNKT cells impact the survival and polarization of pro-inflammatory M1-like and anti-inflammatory M2-like monocyte-derived macrophages. By performing in vitro iNKT cell-macrophage co-cultures followed by flow cytometry analysis, we demonstrated that antigen-stimulated iNKT cells induce a generalized activated state on all macrophage subsets, leading to upregulation of CD40 and CD86 expression. CD40L blocking with a specific monoclonal antibody prior to co-cultures abrogated CD40 and CD86 upregulation, thus indicating that iNKT cells required CD40-CD40L co-stimulation to trigger macrophage activation. In addition, activated iNKT cells were cytotoxic towards macrophages in a CD1d-dependent manner, killing M1-like macrophages more efficiently than their naïve M0 or anti-inflammatory M2-like counterparts. Hence, this work highlighted the role of human iNKT cells as modulators of macrophage survival and phenotype, untangling key features of the human macrophage-iNKT cell axis and opening perspectives for future therapeutic modulation.
Keywords: CD1d; CD40L; iNKT cells; immunomodulation; macrophages.