Targeting TLR4 during vaccination boosts MAdCAM-1 ⁺ lymphoid stromal cell activation and promotes the aged germinal center response

Abstract

The failure to generate enduring humoral immunity after vaccination is a hallmark of advancing age. This can be attributed to a reduction in the germinal center (GC) response, which generates long-lived antibody-secreting cells that protect against (re)infection. Despite intensive investigation, the primary cellular defect underlying impaired GCs in aging has not been identified. Here, we used heterochronic parabiosis to demonstrate that GC formation was dictated by the age of the lymph node (LN) microenvironment rather than the age of the immune cells. Lymphoid stromal cells are a key determinant of the LN microenvironment and are also an essential component underpinning GC structure and function. Using mouse models, we demonstrated that mucosal adressin cell adhesion molecule–1 (MAdCAM-1)–expressing lymphoid stromal cells were among the first cells to respond to NP-KLH + Alum immunization, proliferating and up-regulating cell surface proteins such as podoplanin and cell adhesion molecules. This response was essentially abrogated in aged mice. By targeting TLR4 using adjuvants, we improved the MAdCAM-1 + stromal cell response to immunization. This correlated with improved GC responses in both younger adult and aged mice, suggesting a link between stromal cell responses to immunization and GC initiation. Using bone marrow chimeras, we also found that MAdCAM-1 + stromal cells could respond directly to TLR4 ligands. Thus, the age-associated defect in GC and stromal cell responses to immunization can be targeted to improve vaccines in older people.

B cell‐intrinsic changes with age do not impact antibody‐secreting cell formation but delay B cell participation in the germinal centre reaction

“…Our observations that there are no significant age-related defects in class-switch recombination are concordant with previous in vivo studies by (Dailey et al, 2001) and ex vivo studies on aged mouse follicular B cells by (Russell Knode et al, 2019), but are not consistent with other studies that reported reduced class-switch recombination in aged splenic mouse B cells when stimulated in vitro with CD40L and IL-4 (Frasca et al, 2004(Frasca et al, , 2007. This may suggest some conjoined; B cells from young mice displayed a significant defect in mounting a GC response in an aged lymph node compared to those in a young environment (Denton et al, 2022). This, together with data from our adoptive transfer experiment, suggests that the age of the lymphoid environment, rather than the age of B cells, contributes more to defects in GC formation during ageing.…”

“…When transgenic B cells from a young SW HEL mouse were transferred into young and aged recipient mice, very few of the transferred HEL + B cells were detectable in the aged recipient mice, compared to those transferred into a young environment. These observations match those from heterochronic parabiosis studies, where the circulatory systems of young and aged mice are surgically conjoined; B cells from young mice displayed a significant defect in mounting a GC response in an aged lymph node compared to those in a young environment (Denton et al, 2022 ). This, together with data from our adoptive transfer experiment, suggests that the age of the lymphoid environment, rather than the age of B cells, contributes more to defects in GC formation during ageing.…”

“…This suggests that B cell‐extrinsic factors like poor T cell help and the aged microenvironment are likely more dominant contributors to the age‐related defects in GC response and reduction in antibody response in older individuals (Eaton et al, 2004 ; Lefebvre et al, 2012 ; Stebegg et al, 2020 ; Yang et al, 1996 ). Some factors that have been implicated in causing reduced GC responses in aged mice include defects in the priming of T cells by dendritic cells, impaired T cells help provided to B cells and intrinsic defects in stromal cell activation and function during ageing (Denton et al, 2022 ; Eaton et al, 2004 ; Stebegg et al, 2020 ).…”

Toll-like receptor mediated inflammation directs B cells towards protective antiviral extrafollicular responses

“…Inflammation affected EFR induction in an intrinsic manner, as functional Toll-like receptor (TLR) signaling axes either through MyD88/TRIF or TLR2/4/Unc93b induced optimal activation of the NF-kB c-Rel:IRF4 pathway (Suppl. (Denton et al, 2022).…”

“…Given the above results, we asked how B cell fate dynamics and EFR-derived antibody functionality is affected by repeated antigen exposure with or without TLR agonist provision. For that, all mice were primed with influenza and LPS to ensure equivalent initiation of LN activation (Denton et al, 2022), followed by two additional boosts with antigen alone (Ag Boosted), or antigen plus LPS (Ag+LPS Boosted) or LPS alone (LPS Boosted) as a control (Fig. 8a).…”