IL-18 and Subcapsular Lymph Node Macrophages are Essential for Enhanced B Cell Responses with TLR4 Agonist Adjuvants

Abstract

Designing modern vaccine adjuvants depends on understanding the cellular and molecular events that connect innate and adaptive immune responses. The synthetic TLR4 agonist GLA formulated in a stable emulsion (GLA-SE) augments both cellular and humoral immune responses to vaccine antigens. This adjuvant is currently included in several vaccines undergoing clinical evaluation including those for tuberculosis, leishmaniasis, and influenza. Delineation of the mechanisms of adjuvant activity will enable more informative evaluation of clinical trials. Early after injection, GLA-SE induces substantially more antigen-specific B cells, higher serum antibody titers and greater numbers of T follicular helper (TFH) and TH1 cells than alum, the squalene-in-water emulsion (SE) alone, or GLA without SE. GLA-SE augments antigen-specific B cell differentiation into germinal center and memory precursor B cells as well as pre-plasmablasts that rapidly secrete antibodies. CD169+ SIGNR1+ subcapsular medullary macrophages are the primary cells to take up GLA-SE after immunization and are critical for the innate immune responses, including rapid IL-18 production, induced by GLA-SE. Depletion of subcapsular macrophages (SCMϕ) or abrogation of IL-18 signaling dramatically impairs the antigen-specific B cell and antibody responses augmented by GLA-SE. Depletion of SCMϕ also drastically reduces the TH1 but not TFH response. Thus the GLA-SE adjuvant operates through interaction with IL-18-producing SCMϕ for the rapid induction of B cell expansion and differentiation, antibody secretion and TH1 responses, whereas augmentation of TFH numbers by GLA-SE is independent of SCMϕ.

Old and new adjuvants

“…GLA-SE induces IL-12 production and TH1 cells [110]. When injected into the muscle GLA-SE accumulates in a network of subcapsular macrophages in the draining LNs, driving IL-18-production [112]. These macrophages are required for B cell expansion and differentiation, antibody secretion, and TH1 responses in vaccines using GLA-SE as adjuvant.…”

A combination of TLR-4 agonist and saponin adjuvants increases antibody diversity and protective efficacy of a recombinant West Nile Virus antigen

“…SE), that trigger the NLRP3-dependent inflammasome pathway, and TLR receptors, which stimulate NF-κb via a TRIF- and MyD88-dependent pathway, in the induction of Th1 CD4+ T cells 42 as well as antigen-specific B cells. 43 In the case of Th1 T-cell development, cell intrinsic and extrinsic production of IFNγ has been shown to promote CD69 activation on lymphocytes, which in turn may trap naïve lymphocytes in the draining lymph node alongside antigen-presenting B cells, ultimately driving a Th1 response. Consistent with this model, we observe a number of IFNγ+ T cells following SLA-LSQ in the spleen, and these cells may contribute to the development of a robust Th1 CD4+ T-cell response.…”

TLR4-Induced Inflammation Is a Key Promoter of Tumor Growth, Vascularization, and Metastasis

“…This positive reinforcement ensures sustained expression of downstream targets necessary for prolonged survival, resilience, and heightened activities of immune cells. For instance, LPS-upregulated IL-1 and IL-18 are co-expressed with their receptors that signal through the MyD88 pathway in addition to TLR4 [190] which doubles the outcomes of the combined signaling [191]. LPS-induced co-expression of IL-8, TNF alpha, and other cytokines with their receptors was reported to amplify macrophage functions by enhancing activation of NF-κB [39] and STAT1 [192].…”