HLA‐G inhibition of NK‐cell cytolytic function is uncoupled from tumor cell lipid raft reorganization

Abstract

HLA-G is a non-classical HLA class I molecule with tolerogenic properties and restricted tissue distribution. The expression of HLA-G can be induced by tumors thus providing an efficient way to escape the anti-tumoral immune response. Although lipid rafts regulate diverse immunological mechanisms their relationship with HLA-G remains controversial. Our results show that HLA-G-mediated inhibition of both the interaction between NK and tumor cells, and of intracellular calcium flux in NK cells conjugated to their target cells were independent of lipid raft integrity. In addition, cytotoxicity assays indicated that HLA-G continued to efficiently inhibit NK-cell cytolytic function in several different tumor cells independently of lipid raft integrity. Confocal microscopy with 3D reconstruction combined with biochemical analysis showed that HLA-G was mainly localized outside the lipid rafts of tumor cells after cross-linking with specific antibody and remained excluded from lipid rafts during interaction with the ILT2 inhibitory receptor of NK cells. This study indicates that the inhibitory function of HLA-G is uncoupled from lipid raft organization, further distinguishing HLA-G from classical HLA molecules and providing novel information in the understanding of tumor immune escape mechanism mediated through HLA-G.

Regulation of neutrophil functions through inhibitory receptors: an emerging paradigm in health and disease

“…In this model, neutrophil lipid rafts may serve to bring LILRB2 close to FcγRIIa, thus favoring the dephosphorylation of SYK kinase by SHP‐1, leading to the deactivation of early signaling events critical for cytoskeleton remodeling and neutrophil functions. In line with this model, previous reports show that binding of LILRB1 inhibitory receptor to HLA‐G decreases NK cell signaling and leads to the inhibition of NK cell cytoskeleton reorganization and cytolytic function …”

“…However, HLA‐G expression can be induced by diverse pathological situations, then constituting a potential source of strong ligands for LILRB2 . In this regard, the expression of HLA‐G by tumor cells has been shown to induce escape from immune recognition through the delivery of inhibitory signals to immune effector cells and the induction of a tolerogenic environment …”

Exocytosis acts as a modulator of the ILT4-mediated inhibition of neutrophil functions

“…Stainings were performed as previously described (36). For colocalization experiments, CD32 was capped on neutrophils surface before ILT4 and lipid rafts stainings.…”

Some Basic Aspects of HLA-G Biology

“…However, they present more affinity for HLA-G than for classical HLA-I molecules [75]. Also, HLA-G interaction with LILRB1 on NK cells and the resultant inhibitory function do not require tumor cell lipid raft integrity [76]. This differs from classical HLA-I, which are recruited in lipid rafts upon receptor engagement [77].…”