Lack of T cells in Act1-deficient mice results in elevated IgM-specific autoantibodies but reduced lupus-like disease

Act1 is a negative regulator of B‐cell activation factor of the TNF family (BAFF) and CD40L‐induced signaling. BALB/C mice lacking Act1 develop systemic autoimmunity resembling systemic lupus erythematosus (SLE) and Sjögren's syndrome (SjS). SLE and SjS are characterized by anti‐nuclear IgG autoantibody (ANA‐IgG) production and inflammation of peripheral tissues. As autoantibody production can occur in a T‐cell dependent or T‐cell independent manner, we investigated the role of T‐cell help during Act1‐mediated autoimmunity. Act1‐deficiency was bred onto C57Bl/6 (B6.Act1^?/?) mice and B6.TCRβ^?/?TCRδ^?/?Act1^?/? (TKO) mice were generated. While TCRβ/δ‐sufficient B6.Act1^?/? mice developed splenomegaly and lymphadenopathy, hypergammaglobulinemia, elevated levels of ANA‐IgG, and kidney pathology, TKO mice failed to develop any such signs of disease. Neither B6.Act1^?/? nor TKO mice developed SjS‐like disease, suggesting that epigenetic interactions on the BALB/C background are responsible for this phenotype in BALB/C.Act1^?/? mice. Interestingly, BAFF‐driven transitional B‐cell abnormalities, previously reported in BALB/C.Act1^?/? mice, were intact in B6.Act1^?/? mice and largely independent of T cells. In conclusion, T cells are necessary for the development of SLE‐like disease in B6.Act1^?/? mice, but not BAFF‐driven transitional B‐cell differentiation.     

Increased apoptosis, curtailed expansion and incomplete differentiation of CD8+ T cells combine to decrease clearance of L. monocytogenes in old mice

Aging is accompanied by altered immunity, resulting in a variable state of poorly understood immunodeficiency. While both the numbers and the functionality of naïve T cells are decreased by aging, the impact of these changes upon immune defense against bacterial pathogens in vivo remains understudied. Using a model of Listeria monocytogenes (Lm), where the primary CD8⁺ T‐cell response is critically important for immune defense, we show that C57BL/6 (B6) mice exhibit an age‐dependent reduction in survival, with delayed bacterial clearance in old animals. Kinetic analysis of antigen‐specific CD8⁺ T‐cell expansion showed that CD8⁺ effectors begin dividing at the same time in old and adult mice, but that the proliferative burst remained incomplete during discrete windows of time and was coupled with increased effector apoptosis in old mice. Further, antilisterial CD8⁺ T cells in old mice showed altered expression of key phenotypic and effector molecules and diminished polyfunctionality, measured by the ability to simultaneously produce multiple effector molecules. These results suggest that defects in functional maturation of CD8⁺ cells in aged mice, compounded by (or perhaps coupled to) their reduced expansion in response to infection, yield effector CD8⁺ T‐cell populations insufficient in size and capability to effectively clear newly encountered intracellular pathogens.     

B and CD4+ T‐cell expression of TLR2 is critical for optimal induction of a T‐cell‐dependent humoral immune response to intact Streptococcus pneumoniae

TLR2^?/? mice immunized with Streptococcus pneumoniae (Pn) elicit normal IgM, but defective CD4⁺ T‐cell‐dependent type 1 IgG isotype production, associated with a largely intact innate immune response. We studied the T‐cell‐dependent phosphorylcholine (PC)‐specific IgG3 versus the T‐cell‐independent IgM response to Pn to determine whether TLR2 signals directly via the adaptive immune system. Pn‐activated TLR2^?/? BMDC have only a modest defect in cytokine secretion, undergo normal maturation, and when transferred into naïve WT mice elicit a normal IgM and IgG3 anti‐PC response, relative to WT BMDC. Pn synergizes with BCR and TCR signaling for DNA synthesis in purified WT B and CD4⁺T cells, respectively, but is defective in cells lacking TLR2. Pn primes TLR2^?/? mice for a normal CD4⁺ T‐cell IFN‐γ recall response. Notably, TLR2^?/? B cells transferred into RAG‐2^?/? mice with WT CD4⁺T cells, or TLR2^?/? CD4⁺T cells transferred into athymic nude mice, each elicit a defective IgG3, in contrast to normal IgM, anti‐PC response relative to WT cells. These data are the first to demonstrate a major role for B‐cell and CD4⁺ T‐cell expression of TLR2 for eliciting an anti‐bacterial humoral immune response.     

Mature helper T cell requirement for immunoglobulin production by neonatal naive B cells injected intraperitoneally into severe combined immunodeficient (SCID) mice

It is accepted that human neonatal naive B cells produce mainly IgM in vivo as well as in vitro. Our previous work has demonstrated that i.p. injection of neonatal B cells together with adult mature T cells induces substantial levels of human IgG in the serum of SCID recipient mice. The present study was further attempted to determine the cellular components required for immunoglobulin production by neonatal B cells in SCID mice. When neonatal B and adult T cells were transferred into the SCID mice, human immunoglobulins, largely of IgG, were maximally detected in the serum around 6 weeks after a cell transfer. Depletion of CD4⁺ T cells from adult T cells resulted in undetectable levels of human immunoglobulin in the serum. By contrast, CD4⁺ T cell-enriched populations exhibited an enhancing effect on immunoglobulin production by neonatal B cells. Higher levels of immunoglobulin, including IgA and IgM, were detected in the peritoneal fluid than in the serum as early as 2 weeks after the cell transfer. Human T cells expressing activation antigens such as CD45RO and HLA-DR antigens were identified in the peritoneal lavages. These results suggest that neonatal naive B cells are able to differentiate into cells producing all classes of immunoglobulin in the presence of mature CD4⁺ T cells in a SCID mouse environment. The peritoneal cavity of SCID mice appears to provide a suitable place for immune responses by human cells, possibly in association with a certain xenogeneic reaction.     

Sepsis leads to a reduced antigen-specific primary antibody response

Immunosuppression, impaired cytokine production and high susceptibility to secondary infections are characteristic for septic patients, and for mice after induction of polymicrobial septic peritonitis by sublethal cecal ligation and puncture (CLP). Here, we demonstrate that CLP markedly altered subsequent B‐cell responses. Total IgG and IgM levels, as well as the memory B‐cell response, were increased in septic mice, but antigen‐specific primary antibody production was strongly impaired. We found that two days after CLP, CD11b⁺ splenocytes were activated as demonstrated by the increased expression of activation markers, expression of arginase and production of NO by immature myeloid cells. The in vivo clearance of a bacterial infection was not impaired. DCs demonstrated reduced IL‐12 production and altered antigen presentation, resulting in decreased proliferation but enhanced IFN‐γ production by CD4⁺ cells. CD4⁺ T cells from mice immunized on day 2 after CLP showed reduced Th1 and Th2 cytokine production. In addition, there was an increase in Treg cells. Interestingly, levels of immature B cells decreased but levels of mature B cells increased two days after CLP. However, adoptive transfer of naïve CD4⁺ T cells, naïve B cells, or naïve DCs did not rescue the antigen‐specific antibody response.     

Intrinsic versus environmental influences on T-cell responses in aging

Summary: A decline in T‐cell responses and a switch to memory T‐cell predominance occur with aging. We have used the T‐cell receptor (TCR) transgenic mouse model to study age‐associated changes in T‐cell responses that are a consequence of shifts in subset representation versus changes intrinsic to T cells versus changes in the ‘aged’ microenvironment. We found that naive transgene‐expressing (Tg⁺) CD4⁺ T cells from aged mice respond to antigen with reduced interleukin‐2 (IL‐2) production, decreased cell expansion, and limited differentiation to effectors. Comparable to the characteristic accumulation of memory phenotype T cells in aged humans and conventional rodents, Tg⁺ CD4⁺ T cells from old OTII and 6.5 TCR transgenic mice acquire a memory phenotype without immunization and become hyporesponsive. The naive Tg⁺ CD8⁺ T cells from aged 2C mice expressed activation markers, produced IL‐2, proliferated, and differentiated into cytotoxic T lymphocytes as efficiently as their young counterparts. Responses by adoptive transferred Tg⁺ cells from young mice, immunized in young and old conventional hosts, indicated that the host age influences the onset of cell division, level of cell expansion, and number of cytokine‐producing cells. Co‐transfer of dendritic cells (DCs) from young and less so from aged conventional mice partially restored responses. Furthermore, DCs and T‐cell migration to draining lymphoid organs was reduced due to deficiencies intrinsic to aged cells and the aged environment. Thus, alterations in T‐cell responses in aging are attributable to intrinsic and environmental influences.     

Follicular regulatory T cells repress cytokine production by follicular helper T cells and optimize IgG responses in mice

Follicular helper T (Tfh) cells provide crucial help to germinal center B (GCB) cells for proper antibody production, and a specialized subset of regulatory T cells, follicular regulatory T (Tfr) cells, modulate this process. However, Tfr‐cell function in the GC is not well understood. Here, we define Tfr cells as a CD4⁺ Foxp3⁺ CXCR5^hi PD‐1^hi CD25^low TIGIT^high T‐cell population. Furthermore, we have used a novel mouse model (“Bcl6FC”) to delete the Bcl6 gene in Foxp3⁺ T cells and thus specifically deplete Tfr cells. Following immunization, Bcl6FC mice develop normal Tfh‐ and GCB‐cell populations. However, Bcl6FC mice produce altered antigen‐specific antibody responses, with reduced titers of IgG and significantly increased IgA. Bcl6FC mice also developed IgG antibodies with significantly decreased avidity to antigen in an HIV‐1 gp120 “prime‐boost” vaccine model. In an autoimmune lupus model, we observed strongly elevated anti‐DNA IgA titers in Bcl6FC mice. Additionally, Tfh cells from Bcl6FC mice consistently produce higher levels of Interferon‐γ, IL‐10 and IL‐21. Loss of Tfr cells therefore leads to highly abnormal Tfh‐cell and GCB‐cell responses. Overall, our study has uncovered unique regulatory roles for Tfr cells in the GC response.     

β‐Glucosylceramide ameliorates liver inflammation in murine autoimmune cholangitis

We have demonstrated spontaneous development of autoimmune cholangitis, similar to human primary biliary cirrhosis, in mice expressing a dominant negative form of the transforming growth factor‐β receptor (dnTGF‐βRII) restricted to T cells. The autoimmune cholangitis appears to be mediated by autoreactive CD8⁺ T lymphocytes that home to the portal tracts and biliary system. Because the liver pathology is primarily secondary to CD8⁺ T cells, we have determined herein whether administration of β‐glucosylceramide (GC), a naturally occurring plant glycosphingolipid, alters the natural history of disease in this model. We chose GC because previous work has demonstrated its ability to alter CD8⁺ T cell responses and to down‐regulate tissue inflammation. Accordingly, dnTGF‐βRII mice were treated with either GC or control for a period of 18 weeks beginning at 6 weeks of age. Importantly, in mice that received GC, there was a significant decrease in the frequency and absolute number of autoreactive liver‐infiltrating CD8⁺ T cells, accompanied by a significant decrease in activated CD44^high CD8⁺ T cell populations. Further, there was a significant reduction in portal inflammation in GC‐treated mice. Interestingly, there were no changes in anti‐mitochondrial antibodies, CD4⁺ T cells, CD19⁺ B cells or natural killer (NK) T cell populations, indicating further that the beneficial effects of GC on liver inflammation were targeted specifically to liver‐infiltrating CD8⁺ T cells. These data suggest that further work on GC in models of CD8⁺ T‐mediated inflammation are needed and point to a new therapeutic venue for potentially treating and/or modulating autoimmune disease.     

Effects of type II collagen epitope carbamylation and citrullination in human leucocyte antigen (HLA)‐DR4+ monozygotic twins discordant for rheumatoid arthritis

The aim of this study is to investigate the effect of the native, citrullinated or carbamylated type II human collagen T cell‐ and B cell‐epitopes on the adaptive immune response in rheumatoid arthritis (RA). Peripheral blood T and B cells obtained from a human leucocyte D4‐related (antigen DR4^? HLA‐DR4)⁺ woman with early RA, her healthy monozygotic twin and an unrelated HLA‐DR3⁺ woman with early RA were analysed for activation (CD154/CD69), apoptosis (annexin/7‐aminoactinomycin), cytokine production [interferon (IFN)γ/interleukin (IL)?17/IL‐4/IL‐10/IL‐6] and functional phenotype (CD45Ra/CCR7) after stimulation with the collagen native T cell epitope (T261‐273), the K264 carbamylated T cell epitope (carT261–273), the native B cell epitope (B359–369) or the R360 citrullinated B cell epitope (citB359–369), and the combinations of these. The T cell memory compartment was activated by T cell epitopes in both discordant DR4⁺ twins, but not in the DR3⁺ RA. The collagen‐specific activation of CD4⁺ T cells was induced with both the native and carbamylated T cell epitopes only in the RA twin. Both T cell epitopes also induced IL‐17 production in the RA twin, but a greater IL‐4 and IL‐10 response in the healthy twin. The citrullinated B cell epitope, particularly when combined with the carbamylated T cell epitope, induced B cell activation and an increased IL‐6/IL‐10 ratio in the RA twin compared to a greater IL‐10 production in the healthy twin. Our data suggest that circulating collagen‐specific T and B cells are found in HLA‐DR4⁺ subjects, but only RA activated cells express co‐stimulatory molecules and produce proinflammatory cytokines. Carbamylation and citrullination further modulate the activation and cytokine polarization of T and B cells.     

CD28 controls the development of innate‐like CD8+ T cells by promoting the functional maturation of NKT cells

NK T cells(NKT cells) share functional characteristics and homing properties that are distinct from conventional T cells. In this study, we investigated the contribution of CD28 in the functional development of γδ NKT and αβ NKT cells in mice. We show that CD28 promotes the thymic maturation of promyelocytic leukemia zinc finger⁺ IL‐4⁺ NKT cells and upregulation of LFA‐1 expression on NKT cells. We demonstrate that the developmental defect of γδ NKT cells in CD28‐deficient mice is cell autonomous. Moreover, we show in both wild‐type C57BL/6 mice and in downstream of tyrosine kinase‐1 transgenic mice, a mouse model with increased numbers of γδ NKT cells, that CD28‐mediated regulation of thymic IL‐4⁺ NKT cells promotes the differentiation of eomesodermin⁺ CD44^high innate‐like CD8⁺ T cells. These findings reveal a previously unappreciated mechanism by which CD28 controls NKT‐cell homeostasis and the size of the innate‐like CD8⁺ T‐cell pool.     

Specific CD8+ T cells recognize human herpesvirus 6B

The importance of human herpesvirus 6 (HHV‐6) species as human pathogens is increasingly appreciated. However, we do not understand how infection is controlled in healthy virus carriers, and why control fails in patients with disease. Other persistent viruses are under continuous surveillance by antigen‐specific T cells, and specific T‐cell repertoires have been well characterized for some of them. In contrast, knowledge on HHV‐6‐specific T‐cell responses is limited, and missing for CD8⁺ T cells. Here we identify CD8⁺ T‐cell responses to HHV‐6B, the most widespread HHV‐6 species, in healthy virus carriers. HHV‐6B‐specific CD8⁺ T‐cell lines and clones recognized HLA‐A2‐restricted peptides from the viral structural proteins U54 and U11, and displayed various antigen‐specific antiviral effector functions. These CD8⁺ T cells specifically recognized HHV‐6B‐infected primary CD4⁺ T cells in an HLA‐restricted manner, produced antiviral cytokines, and killed infected cells, whereas HHV‐6A‐infected cells were not recognized. Thus, HHV‐6B‐specific CD8⁺ T cells are likely to contribute to control of infection, overcoming the immunomodulatory effects exerted by the virus. Potentially, HHV‐6‐associated disease could be addressed by active or passive immunotherapy that reconstitutes virus‐specific CD8⁺ T‐cell responses.     

Impaired antigen‐specific lymphocyte priming in mice after Toll‐like receptor 4 activation via induction of monocytic myeloid‐derived suppressor cells

In sepsis, the pathology involves a shift from a proinflammatory state toward an immunosuppressive phase. We previously showed that an agonistic anti‐TLR4 antibody induced long‐term endotoxin tolerance and suppressed antigen‐specific secondary IgG production when primed prior to immunization with antigen. These findings led us to speculate that TLR4‐induced innate tolerance due to primary infection causes an immunosuppressive pathology in sepsis. Therefore, the mechanism underlying impaired antigen‐specific humoral immunity by the TLR4 antibody was investigated. We showed, in a mouse model, that primary antigen‐specific IgG responses were impaired in TLR4 antibody‐induced tolerized mice, which was the result of reduced numbers of antigen‐specific GC B cells and plasma cells. Ovalbumin‐specific CD4 and CD8 T‐cell responses were impaired in TLR4 antibody‐injected OT‐I and ‐II transgenic mice ex vivo. Adoptive transfer studies demonstrated suppression of OVA‐specific CD4 and CD8 T‐cell responses by the TLR4 antibody in vivo. The TLR4 antibody induced Gr1⁺CD11b⁺ myeloid‐derived suppressor cell (MDSC) expansion with suppression of T‐cell activation. Monocytic MDSCs were more suppressive and exhibited higher expression of PD‐L1 and inducible nitric oxidase compared with granulocytic MDSCs. In conclusion, immune tolerance conferred by TLR4 activation induces the expansion of monocytic MDSCs, which impairs antigen‐specific T‐cell priming and IgG production.     

Non-tolerant B cells cause autoimmunity in anti-CD8 IgG2a-transgenic mice

Using a pair of γ2a/x immunoglobulin genes, transgenic mice were generated to study tolerance induction in B cells that express IgG2a autoantibodies. The transgenic IgG2a specifically binds CD8 α chains of the CD8.2 allotype expressed on the surface of CD8⁺ T cells, but not CD8 molecules expressed by the CD8.1 allele. Thus, IgG2a transgenic mice expressing the CD8.1 allele were used as controls to monitor B cell development and mice expressing CD8.2 were used to study B cell tolerance. Both types of mice showed transgenic γ2a expression on the surface of B cells. Expression of endogenous heavy chain alleles was strongly inhibited in immature B cell subsets, whereas mature B cells co-expressed transgenic γ2a and endogenous IgM/D. The transgenic x chain expression leads only to partial allelic exclusion of endogenous light chains. B cells that express high levels of transgenic CD8.2-specific IgG2a were identified using soluble CD8-Ig. In CD8.1⁺ and in CD8.2⁺ mice, we found no differences in expression and maturation of transgenic anti-CD8.2 IgG2a⁺ B cells. High levels of serum anti-CD8.2 IgG2a antibodies led to the elimination of CD8⁺ T cells, causing a severe defect in cytotoxic immune responses. These results show that tolerance induction is incomplete in the CD8.2⁺ mice, either because IgG2a⁺ B cells are resistant to censoring mechanisms or because the secreted CD8-specific IgG2a antibodies render the CD8 autoantigen inaccessible to the B cells. This contrasts strongly with the efficient induction of B cell tolerance in mice expressing anti-CD8.2 IgM autoantibodies.     

Unexpected involvement of IL‐13 signalling via a STAT6 independent mechanism during murine IgG2a development following viral vaccination

In this study, recombinant pox viral vaccination was shown to induce highly elevated IgG2a and low IgG1 antibody expression in mice lacking IL‐4 or STAT6, whilst IL‐13^?/? mice exhibited elevated IgG1, but very low IgG2a. These findings revealed that IL‐13 and IL‐4 differentially regulated antibody development. To understand this further, when STAT6^?/? mice were given a vaccine co‐expressing IL‐13Rα2 that temporarily sequestered IL‐13, significantly reduced IgG2a expression, was detected. These findings for the first time demonstrated that IL‐13 regulated IgG2a differentiation utilising an alternative IL‐13R signalling pathway independent of STAT6 (IL‐13Rα2 pathway). This was further corroborated by the (i) elevated IL‐13Rα2 expression detected on STAT6^?/? lung MHCII⁺ CD11c⁺ cells 24 h post IL‐13 inhibitor vaccination and ii) significant up‐regulation of IL‐13Rα2 expression on spleen and lung derived MHCII⁺CD11c⁺ following inhibition of STAT6 signalling in vitro, or vaccination with IL‐4R/STAT6 antagonist in vivo. When T follicular helper (Tfh) cells which regulate antibody differentiation were assessed post vaccination, although no difference in IL‐4 expression was observed, greatly reduced IFN‐γ expression was detected in IL‐13^?/? and STAT6^?/? mice compared to wild‐type. These findings support the notion that the balance of IL‐13 level at the vaccination site can differentially regulate T and B‐cell immune outcomes.     

Circulating immunoglobulin-bound transforming growth factor beta at a late tumour-bearing stage impairs antigen-specific responses of CD4+ T cells

In order to elucidate the mechanisms by which tumour‐specific CD4⁺ T‐cell responses are impaired during tumour development, an attempt was made to identify factors which impair CD4⁺ T‐cell responses at a late tumour‐bearing stage. Plasma from mice bearing B16 melanoma for 30 days (plasma d30) showed a more profound immunosuppressive effect on the in vitro proliferation of unrelated antigen‐specific CD4⁺ T cells in the presence of both antigen and antigen‐presenting cells (APC) than plasma from naïve mice. The level of plasma transforming growth factor (TGF)‐β was elevated in mice bearing B16 melanoma for 30 days compared with naïve mice, and the suppressive effect of plasma d30 was partially diminished by the neutralization of TGF‐β. Interestingly, immunoglobulin (IgG)‐bound TGF‐β, but not IgG‐unbound TGF‐β, in plasma d30 was suggested to be responsible for the immunosuppressive activity. In addition, no suppressive effect of plasma d30 was observed when antigen was added as a class II peptide, thus suggesting that the impaired proliferation of CD4⁺ T cells in the presence of plasma d30 was due to a dysfunction of antigen uptake/processing by APC. Furthermore, dissociation between IgG and TGF‐β resulted in a loss of the suppressive activity of plasma d30. Taken together, these results suggest that circulating IgG‐bound TGF‐β is, at least in part, responsible for the impaired responses of CD4⁺ T cells at the late tumour‐bearing stage by suppressing antigen uptake/ processing by APC.     

Cardiolipin activates antigen‐presenting cells via TLR2‐PI3K‐PKN1‐AKT/p38‐NF‐kB signaling to prime antigen‐specific naïve T cells in mice

Mitochondrial defects and antimitochondrial cardiolipin (CL) antibodies are frequently detected in autoimmune disease patients. CL from dysregulated mitochondria activates various pattern recognition receptors, such as NLRP3. However, the mechanism by which mitochondrial CL activates APCs as a damage‐associated molecular pattern to prime antigen‐specific naïve T cells, which is crucial for T‐cell‐dependent anticardiolipin IgG antibody production in autoimmune diseases is unelucidated. Here, we show that CL increases the expression of costimulatory molecules in CD11c⁺ APCs both in vitro and in vivo. CL activates CD11c⁺ APCs via TLR2‐PI3K‐PKN1‐AKT/p38MAPK‐NF‐κB signaling. CD11c⁺ APCs that have been activated by CL are sufficient to prime H‐Y peptide‐specific naïve CD4⁺ T cells and OVA‐specific naïve CD8⁺ T cells. TLR2 is necessary for anti‐CL IgG antibody responses in vivo. Intraperitoneal injection of CL does not activate CD11c⁺ APCs in CD14 KO mice to the same extent as in wild‐type mice. CL binds to CD14 (Kd = 7 × 10^?7 M). CD14, but not MD2, plays a role in NF‐kB activation by CL, suggesting that CD14⁺ macrophages contribute to recognizing CL. In summary, CL activates signaling pathways in CD11c⁺ APCs through a mechanism similar to gram (+) bacteria and plays a crucial role in priming antigen‐specific naïve T cells.     

Residual LCMV antigen in transiently CD4+ T cell‐depleted mice induces high levels of virus‐specific antibodies but only limited B‐cell memory

Infection of C57BL/6 mice with lymphocytic choriomeningitis virus (LCMV) strain Armstrong (Arm) induces an acute infection with rapid virus clearance by CD8⁺ T cells independently of CD4⁺ T cell help. Residual viral antigen may, however, persist for a prolonged time. Here, we demonstrate that mice that had been transiently depleted of CD4⁺ T cells during acute LCMV Arm infection generated high levels of virus‐specific IgG antibodies (Ab) after viral clearance. Robust induction of LCMV‐specific IgG after transient CD4⁺ T cell depletion was dependent on Fcγ receptors but not on the complement receptors CD21/CD35. In contrast to the potent production of LCMV‐specific IgG, the generation of LCMV‐specific isotype‐switched memory B cells after transient CD4⁺ T cell depletion was considerably reduced. Moreover, mice depleted of CD4⁺ T cells during acute infection were strongly impaired in generating a secondary LCMV‐specific B cell response upon LCMV rechallenge. In conclusion, our data indicate that LCMV antigen depots after viral clearance were capable of inducing high levels of virus‐specific IgG. They failed, however, to induce robust virus‐specific B cell memory revealing a previously unappreciated dichotomy of specific Ab production and memory cell formation after priming with residual antigen.