Germinal center expansion but not plasmablast differentiation is proportional to peptide-MHCII density via CD40-CD40L signaling strength

T follicular helper (TFH) cells promote expansion of germinal center (GC) B cells and plasma cell differentiation. Whether cognate peptide-MHCII (pMHCII) density instructs selection and cell fate decisions in a quantitative manner remains unclear. Using αDEC205-OVA to differentially deliver OVA peptides to GC B cells on the basis of DEC205 allelic copy number, we find DEC205+/+ B cells take up 2-fold more antigen than DEC205+/- cells, leading to proportional TFH cell help and B cell expansion. To validate these results, we establish a caged OVA peptide, which is readily detected by OVA-specific TFH cells after photo-uncaging. In situ uncaging of peptides leads to multiple serial B-T contacts and cell activation. Differential CD40 signaling, is both necessary and sufficient to mediate 2-fold differences in B cell expansion. While plasmablast numbers are increased, pMHCII density does not directly control the output or quality of plasma cells. Thus, we distinguish the roles TFH cells play in expansion versus differentiation.

Germinal center expansion but not plasmablast differentiation is directly proportional to peptide-MHCII density via CD40-CD40L signaling strength

Although cognate peptide-MHCII (pMHCII) is critical for B cell selection in the germinal center (GC), it is unclear how cell intrinsic differences in peptide levels contribute to selection and cell fate decisions. Here, we applied the a-DEC205-OVA (dec) model system, to deliver different levels of OVA peptide to GC B cells in situ in order to interrogate how intermediate and high levels of pMHCII affect selection and cell fate on a per cell basis. We used Ly75+/− (DEC-het) B cells, which expressed ~50% of surface DEC205 protein compared to WT B cells, and presented proportional amount of OVA peptide after dec treatment. Using competitive co-transfers, we found that WT B cells expanded two-fold more than DEC-het B cells. This 2-fold difference in expansion was maintained at a wide range of dec administration. To study T cell recognition in situ, we developed a novel caged ovalbumin peptide, which is readily detected by OT-II T cells upon photo-uncaging, and revealed that initial T cell recognition in the GC leads to increased B-T serial contacts. Differential CD40 signaling, was both necessary and sufficient to mediate 2-fold differences in GC B cell expansion and also promoted GC-like B cell morphology, suggesting CD40 signaling is a rheostat of pMHCII dose. Surprisingly, we found that while plasmablast numbers were increased upon dec stimulation, both WT and DEC-het GC B cells were equally capable of differentiating into plasma cells, suggesting that pMHCII density does not directly control the output or quality of plasma cells generated. Thus, these results delineate distinct roles pMHCII play in expansion vs. differentiation in the GC.

Supported by grants from NIH (R01 HL141491-05)

IL-1 and IL-1ra are key regulators of the inflammatory response to RNA vaccines

The use of lipid-formulated RNA vaccines for cancer or COVID-19 is associated with dose-limiting systemic inflammatory responses in humans that were not predicted from preclinical studies. Here, we show that the 'interleukin 1 (IL-1)-interleukin 1 receptor antagonist (IL-1ra)' axis regulates vaccine-mediated systemic inflammation in a host-specific manner. In human immune cells, RNA vaccines induce production of IL-1 cytokines, predominantly IL-1β, which is dependent on both the RNA and lipid formulation. IL-1 in turn triggers the induction of the broad spectrum of pro-inflammatory cytokines (including IL-6). Unlike humans, murine leukocytes respond to RNA vaccines by upregulating anti-inflammatory IL-1ra relative to IL-1 (predominantly IL-1α), protecting mice from cytokine-mediated toxicities at >1,000-fold higher vaccine doses. Thus, the IL-1 pathway plays a key role in triggering RNA vaccine-associated innate signaling, an effect that was unexpectedly amplified by certain lipids used in vaccine formulations incorporating N1-methyl-pseudouridine-modified RNA to reduce activation of Toll-like receptor signaling.

Dynamic CD138 surface expression regulates switch between myeloma growth and dissemination

The canonical plasma cell marker CD138 (syndecan-1) is highly expressed on the myeloma cell surface, but its functional role in vivo is unclear, as well as the ontogeny of CD138-high and CD138-negative (neg) myeloma cells. In this study we used an in vivo murine Vk*MYC myeloma model where CD138 is heterogeneously expressed depending on tumor size. We find that in comparison to CD138-neg myeloma cells, the CD138-high subset of myeloma cells is highly proliferative, less apoptotic, and enhanced IL-6R signaling, which is known to promote survival. In addition CD138-high myeloma engrafts better than its CD138-neg counterpart. In contrast, CD138-neg cells are more motile both in vitro and in vivo, and more readily disseminate and spread to other bones in vivo than CD138-high subset. Neutralizing CD138 rapidly triggers migration of myeloma cells in vivo and leads to intravasation, which results in increased dissemination to other bones. Both murine and human myeloma cells can rapidly recycle CD138 surface expression through endocytic trafficking, in response to serum levels. Blocking CD138 enhances myeloma sensitivity to bortezomib chemotherapy and significantly reduces tumor size compared to bortezomib treatment alone. Thus, our data show that CD138 surface expression dynamically regulates a switch between growth vs. dissemination for myeloma, in response to nutrient conditions.

Targeting netrin-1/DCC interaction in diffuse large B-cell and mantle cell lymphomas

DCC (Deleted in Colorectal Carcinoma) has been demonstrated to constrain tumor progression by inducing apoptosis unless engaged by its ligand netrin‐1. This has been shown in breast and colorectal cancers; however, this tumor suppressive function in other cancers is not established. Using a transgenic mouse model, we report here that inhibition of DCC‐induced apoptosis is associated with lymphomagenesis. In human diffuse large B‐cell lymphoma (DLBCL), an imbalance of the netrin‐1/DCC ratio suggests a loss of DCC‐induced apoptosis, either via a decrease in DCC expression in germinal center subtype or by up‐regulation of netrin‐1 in activated B‐cell (ABC) one. Such imbalance is also observed in mantle cell lymphoma (MCL). Using a netrin‐1 interfering antibody, we demonstrate both in vitro and in vivo that netrin‐1 acts as a survival factor for ABC‐DLBCL and MCL tumor cells. Together, these data suggest that interference with the netrin‐1/DCC interaction could represent a promising therapeutic strategy in netrin‐1‐positive DLBCL and MCL.

TGF-β prevents T follicular helper cell accumulation and B cell autoreactivity

T follicular helper (Tfh) cells contribute to the establishment of humoral immunity by controlling the delivery of helper signals to activated B cells; however, Tfh development must be restrained, as aberrant accumulation of these cells is associated with positive selection of self-reactive germinal center B cells and autoimmunity in both humans and mice. Here, we show that TGF-β signaling in T cells prevented Tfh cell accumulation, self-reactive B cell activation, and autoantibody production. Using mice with either T cell-specific loss or constitutive activation of TGF-β signaling, we demonstrated that TGF-β signaling is required for the thymic maturation of CD44⁺CD122⁺Ly49⁺CD8⁺ regulatory T cells (Tregs), which induce Tfh apoptosis and thus regulate this cell population. Moreover, peripheral Tfh cells escaping TGF-β control were resistant to apoptosis, exhibited high levels of the antiapoptotic protein BCL2, and remained refractory to regulation by CD8+ Tregs. The unrestrained accumulation of Tfh cells in the absence of TGF-β was dependent on T cell receptor engagement and required B cells. Together, these data indicate that TGF-β signaling restrains Tfh cell accumulation and B cell-associated autoimmunity and thereby controls self-tolerance.

Blockade of B7-H1 (programmed death ligand 1) enhances humoral immunity by positively regulating the generation of T follicular helper cells

T follicular helper (T(FH)) cells are critical initiators in the development of T cell-dependent humoral immunity and the generation of protective immunity. We demonstrate that T(FH) cell accumulation and Ab production are negatively regulated by B7-H1 (programmed death ligand 1) in response to both helminth infection and active immunization. Following immunization of B7-H1(-/-) mice with keyhole limpet hemocyanin or helminth Ags, there is a profound increase in induction of T(FH) cells as a result of increased cell cycling and decreased apoptosis relative to wild-type mice. The increase in T(FH) cells in the absence of B7-H1 was associated with significant elevations in Ag-specific Ig response. Cotransfer experiments in vivo demonstrated that B7-H1 expression on B cells was required for negatively regulating T(FH) cell expansion and production of Ag-specific Ig. Treatment of immunized wild-type mice with anti-B7-H1 or anti-programmed death 1 mAbs, but not anti-B7-DC, led to a significant expansion of the T(FH) cell population and an enhanced Ag-specific Ig response. Our results demonstrate that the coinhibitory B7-H1/programmed death 1 pathway can limit the expansion of T(FH) cells and constrain Ag-specific Ig responses. This finding has direct implications for investigations examining the feasibility of therapeutically manipulating this pathway and reveals new insights into the regulation of the humoral immune response.

Neonatal CD8+ T-cell differentiation is dependent on interleukin-12

Neonatal CD8(+) T-cell activation is significantly impaired compared with that in adults. Recent studies have demonstrated that interleukin (IL)-12 is necessary as a third signal, in addition to antigen and co-stimulation, to authorize the differentiation of naive CD8(+) T cells. We examined whether human neonatal CD8(+) T cells, which possess an exclusively naive T-cell phenotype, required a third signal to authorize a productive T-cell response. IL-12 enhanced activated naive CD8(+) T-cell survival, expansion, CD25 expression, and IL-2 production. Activated CD8(+) T cells produced interferon-γ and intracellular granzyme B and were cytotoxic only in the presence of IL-12. Sustained IL-12 signaling for 72 hours was required for optimal interferon-γ production. IL-12, in concert with T cell receptor (TCR) stimulation, sustained late-stage (48-72 hours) intracellular phosphorylation and particularly total protein levels of the proximal TCR components, Lck, and CD3ξ. The requirement for a third signal for productive human neonatal CD8(+) T-cell differentiation may have implications for neonatal vaccination strategies.

Iridocyclitis and an Iris Mass Associated with Secondary Syphilis

A 34-year-old white man developed iridocyclitis and an iris mass. The iridocyclitis was preceded by a nodular rash which spared the palms and soles. An anterior segment fluorescein angiogram was performed which showed numerous permeable vessels. An ultrasound examination of the mass showed that it extended to the ciliary body. He had both a positive RPRCT and FTA-Abs. A skin biopsy was done which disclosed the nodules to be a rare form of secondary syphilis. The patient was treated with topical steroids and a cycloplegic agent, and later prednisone and intravenous penicillin, with eventual resolution of iris mass, iridocyclitis and skin nodules.

Lysyl oxidase and collagenase in experimental acute and chronic liver injury

Lysyl oxidase and collagenase activities were measured in experimental acute and chronic liver injury in mice and rats, and correlated with collagen synthesis and accumulation. Acute liver injury was induced in mice and rats by a single dose of carbon tetrachloride given by gavage, and also in mice by a single injection of murine hepatitis virus. Chronic liver injury was induced in rats by repeated injections of carbon tetrachloride. Elevated plasma glutamic oxaloacetic transaminase levels, increased hepatic prolyl hydroxylase activity, and increased synthesis of collagen-bound hepatic hydroxyproline occurred in animals with acute as well as with chronic liver injury. However, only chronic liver injury appeared to be associated with fibrosis, increased collagen-bound hydroxyproline content, increased hepatic lysyl oxidase and collagenase activities, as well as with increased serum lysyl oxidase activity. These data suggest that lysyl oxidase and collagenase may play an important role in the collagen accumulation associated with hepatic fibrosis.