The characterization of CD8+ T-cell responses in COVID-19

This review gives an overview of the protective role of CD8+ T cells in SARS-CoV-2 infection. The cross-reactive responses intermediated by CD8+ T cells in unexposed cohorts are described. Additionally, the relevance of resident CD8+ T cells in the upper and lower airway during infection and CD8+ T-cell responses following vaccination are discussed, including recent worrisome breakthrough infections and variants of concerns (VOCs). Lastly, we explain the correlation between CD8+ T cells and COVID-19 severity. This review aids in a deeper comprehension of the association between CD8+ T cells and SARS-CoV-2 and broadens a vision for future exploration.

Intrinsic factors and CD1d1 but not CD1d2 expression levels control invariant natural killer T cell subset differentiation

Invariant natural killer T (NKT) cell subsets are defined based on their cytokine-production profiles and transcription factors. Their distribution is different in C57BL/6 (B6) and BALB/c mice, with a bias for NKT1 and NKT2/NKT17 subsets, respectively. Here, we show that the non-classical class I-like major histocompatibility complex CD1 molecules CD1d2, expressed in BALB/c and not in B6 mice, could not account for this difference. We find however that NKT cell subset distribution is intrinsic to bone marrow derived NKT cells, regardless of syngeneic CD1d-ligand recognition, and that multiple intrinsic factors are likely involved. Finally, we find that CD1d expression levels in combination with T cell antigen receptor signal strength could also influence NKT cell distribution and function. Overall, this study indicates that CD1d-mediated TCR signals and other intrinsic signals integrate to influence strain-specific NKT cell differentiation programs and subset distributions.

The role of Raptor in lymphocytes differentiation and function

Raptor, a key component of mTORC1, is required for recruiting substrates to mTORC1 and contributing to its subcellular localization. Raptor has a highly conserved N-terminus domain and seven WD40 repeats, which interact with mTOR and other mTORC1-related proteins. mTORC1 participates in various cellular events and mediates differentiation and metabolism. Directly or indirectly, many factors mediate the differentiation and function of lymphocytes that is essential for immunity. In this review, we summarize the role of Raptor in lymphocytes differentiation and function, whereby Raptor mediates the secretion of cytokines to induce early lymphocyte metabolism, development, proliferation and migration. Additionally, Raptor regulates the function of lymphocytes by regulating their steady-state maintenance and activation.

The role of regulatory T cells and follicular T helper cells in HBV infection

Hepatitis B has become one of the major global health threats, especially in developing countries and regions. Hepatitis B virus infection greatly increases the risk for liver diseases such as cirrhosis and cancer. However, treatment for hepatitis B is limited when considering the huge base of infected people. The immune response against hepatitis B is mediated mainly by CD8+ T cells, which are key to fighting invading viruses, while regulatory T cells prevent overreaction of the immune response process. Additionally, follicular T helper cells play a key role in B-cell activation, proliferation, differentiation, and formation of germinal centers. The pathogenic process of hepatitis B virus is generally the result of a disorder or dysfunction of the immune system. Therefore, we present in this review the critical functions and related biological processes of regulatory T cells and follicular T helper cells during HBV infection.

The role of dendritic cells in COVID-19 infection

The persistent pandemic of coronavirus disease in 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) currently poses a major infectious threat to public health around the world. COVID-19 is an infectious disease characterized by strong induction of inflammatory cytokines, progressive lung inflammation, and potential multiple organ dysfunction. SARS-CoV-2 infection is closely related to the innate immune system and adaptive immune system. Dendritic cells (DCs), as a "bridge" connecting innate immunity and adaptive immunity, play many important roles in viral diseases. In this review, we will pay special attention to the possible mechanism of dendritic cells in human viral transmission and clinical progression of diseases, as well as the reduction and dysfunction of DCs in severe SARS-CoV-2 infection, so as to understand the mechanism and immunological characteristics of SARS-CoV-2 infection.

B cell-T cell interplay in immune regulation: A focus on follicular regulatory T and regulatory B cell functions

B cells are the core components of humoral immunity. A mature B cell can serve in multiple capacities, including antibody production, antigen presentation, and regulatory functions. Forkhead box P3 (FoxP3)-expressing regulatory T cells (Tregs) are key players in sustaining immune tolerance and keeping inflammation in check. Mounting evidence suggests complex communications between B cells and Tregs. In this review, we summarize the yin-yang regulatory relationships between B cells and Tregs mainly from the perspectives of T follicular regulatory (Tfr) cells and regulatory B cells (Bregs). We discuss the regulatory effects of Tfr cells on B cell proliferation and the germinal center response. Additionally, we review the indispensable role of B cells in ensuring homeostatic Treg survival and describe the function of Bregs in promoting Treg responses. Finally, we introduce a new subset of Tregs, termed Treg-of-B cells, which are induced by B cells, lake the expression of FoxP3 but still own immunomodulatory effects. In this article, we also enumerate a sequence of research from clinical patients and experimental models to clarify the role of Tfr cells in germinal centers and the role of convention B cells and Bregs to Tregs in the context of different diseases. This review offers an updated overview of immunoregulatory networks and unveils potential targets for therapeutic interventions against cancer, autoimmune diseases and allograft rejection.

The role of B cells in COVID-19 infection and vaccination

B cells secrete antibodies and mediate the humoral immune response, making them extremely important in protective immunity against SARS-CoV-2, which caused the coronavirus disease 2019 (COVID-19) pandemic. In this review, we summarize the positive function and pathological response of B cells in SARS-CoV-2 infection and re-infection. Then, we structure the immunity responses that B cells mediated in peripheral tissues. Furthermore, we discuss the role of B cells during vaccination including the effectiveness of antibodies and memory B cells, viral evolution mechanisms, and future vaccine development. This review might help medical workers and researchers to have a better understanding of the interaction between B cells and SARS-CoV-2 and broaden their vision for future investigations.

PLZF Acetylation Levels Regulate NKT Cell Differentiation

The transcription factor promyelocytic leukemia zinc finger (PLZF) is encoded by the BTB domain-containing 16 (Zbtb16) gene. Its repressor function regulates specific transcriptional programs. During the development of invariant NKT cells, PLZF is expressed and directs their effector program, but the detailed mechanisms underlying PLZF regulation of multistage NKT cell developmental program are not well understood. This study investigated the role of acetylation-induced PLZF activation on NKT cell development by analyzing mice expressing a mutant form of PLZF mimicking constitutive acetylation (PLZF^ON) mice. NKT populations in PLZF^ON mice were reduced in proportion and numbers of cells, and the cells present were blocked at the transition from developmental stage 1 to stage 2. NKT cell subset differentiation was also altered, with T-bet⁺ NKT1 and RORγt⁺ NKT17 subsets dramatically reduced and the emergence of a T-bet^-RORγt^- NKT cell subset with features of cells in early developmental stages rather than mature NKT2 cells. Preliminary analysis of DNA methylation patterns suggested that activated PLZF acts on the DNA methylation signature to regulate NKT cells' entry into the early stages of development while repressing maturation. In wild-type NKT cells, deacetylation of PLZF is possible, allowing subsequent NKT cell differentiation. Interestingly, development of other innate lymphoid and myeloid cells that are dependent on PLZF for their generation is not altered in PLZF^ON mice, highlighting lineage-specific regulation. Overall, we propose that specific epigenetic control of PLZF through acetylation levels is required to regulate normal NKT cell differentiation.

Characterization of the developmental landscape of murine RORγt+ iNKT cells

Invariant natural killer T (iNKT) cells expressing the retinoic acid receptor-related orphan receptor γt (RORγt) and producing IL-17 represent a minor subset of CD1d-restricted iNKT cells (iNKT17) in C57BL/6J (B6) mice. We aimed in this study to define the reasons for their low distribution and the sequence of events accompanying their normal thymic development. We found that RORγt+ iNKT cells have higher proliferation potential and a greater propensity to apoptosis than RORγt- iNKT cells. These cells do not likely reside in the thymus indicating that thymus emigration, and higher apoptosis potential, could contribute to RORγt+ iNKT cell reduced thymic distribution. Ontogeny studies suggest that mature HSAlow RORγt+ iNKT cells might develop through developmental stages defined by a differential expression of CCR6 and CD138 during which RORγt expression and IL-17 production capabilities are progressively acquired. Finally, we found that RORγt+ iNKT cells perceive a strong TCR signal that could contribute to their entry into a specific 'Th17 like' developmental program influencing their survival and migration. Overall, our study proposes a hypothetical thymic developmental sequence for iNKT17 cells, which could be of great use to study molecular mechanisms regulating this developmental program.

Cortical Thymocytes Along With Their Selecting Ligands Are Required for the Further Thymic Maturation of NKT Cells in Mice

Following positive selection, NKT cell precursors enter an “NK-like” program and progress from an NK^– to an NK⁺ maturational stage to give rise to NKT1 cells. Maturation takes place in the thymus or after emigration of NK^– NKT cells to the periphery. In this study, we followed the fate of injected NKT cells at the NK^– stage of their development in the thymus of a series of mice with differential CD1d expression. Our results indicate that CD1d-expressing cortical thymocytes, and not epithelial cells, macrophages, or dendritic cells, are necessary and sufficient to promote the maturation of thymic NKT1 cells. Migration out of the thymus of NK^– NKT cells occurred in the absence of CD1d expression, however, CD1d expression is required for maturation in peripheral organs. We also found that the natural ligand Isoglobotriosylceramide (iGb3), and the cysteine protease Cathepsin L, both localizing with CD1d in the endosomal compartment and crucial for NKT cell positive selection, are also required for NK^– to NK⁺ NKT cell transition. Overall, our study indicates that the maturational transition of NKT cells require continuous TCR/CD1d interactions and suggest that these interactions occur in the thymic cortex where DP cortical thymocytes are located. We thus concluded that key components necessary for positive selection of NKT cells are also required for subsequent maturation.

A focus on natural killer T-cell subset characterization and developmental stages

Almost 20 years ago, CD1d tetramers were developed to track invariant natural killer T (NKT) cells based on their specificity, and to define developmental steps during which differentiation markers and functional features are progressively acquired from early NKT cell precursor to fully mature NKT cell subsets. Based on these findings, a linear developmental model was proposed and subsequently used by all studies investigating the specific role of factors that control NKT cell development. More recently, based on intracellular staining patterns of lineage-specific transcription factors such as T-bet, GATA-3, promyelocytic leukemia zinc finger and RORγt, a lineage differentiation model was proposed for NKT cell development. Currently, studies on NKT cells development present lineage differentiation model data in addition to the linear maturation model. In the perspective presented here, we discuss current knowledge relating to NKT cell developmental models and particularly focus on the approaches and strategies, some of which appear nebulous, used to define NKT cell developmental stages and subsets.

Critical Contribution of NK Group 2 Member D Expressed on Invariant Natural Killer T Cells in Concanavalin A-Induced Liver Hepatitis in Mice

Natural killer group 2D (NKG2D) is a well-characterized activating receptor expressed on many immune cells, including invariant natural killer T (iNKT) cells. These cells were shown to be responsible of liver injury in the model of concanavalin A (Con A)-induced hepatitis, considered to be an experimental model of human autoimmune hepatitis. In this study, we investigated whether NKG2D plays a role in the hepatitis induced by iNKT cell-mediated immune response to Con A. By using killer cell lectin-like receptor subfamily K, member 1 deficient (Klrk1^−/−) mice, we found that the absence of NKG2D reduced the hepatic injury upon Con A administration. This was not due to an intrinsic functional defect of NKG2D-deficient iNKT cells as mice missing NKG2D have normal distribution and function of iNKT cells. Furthermore, increased resistance to Con A-induced hepatitis was confirmed using neutralizing anti-NKG2D antibodies. The reduced pathogenic effect of Con A in the absence of NKG2D correlates with a reduction in pathogenic cytokine production and FAS-Ligand (FAS-L) expression by iNKT cells. We also found that Con A administration led to an increase in the retinoic acid early inducible (RAE-1) surface expression on wild-type hepatocytes. Finally, we found that Con A has no direct action on FAS-L expression or cytokine production by iNKT cells and thus propose that NKG2D-L expression on stressed hepatocytes promote cytotoxic activity of iNKT cells via its interaction with NKG2D contributing to hepatic injury. In conclusion, our results highlight NKG2D as an essential receptor required for the activation of iNKT cells in Con A-induced hepatitis and indicate that it represents a potential drug target for prevention of autoimmune hepatitis.

Potential role of IL-17-producing iNKT cells in type 1 diabetes

We explored in this study the status and potential role of IL-17-producing iNKT cells (iNKT17) in type 1 diabetes (T1D) by analyzing these cells in patients with T1D, and in NOD mice, a mouse model for T1D. Our analysis in mice showed an increase of iNKT17 cells in NOD vs control C57BL/6 mice, partly due to a better survival of these cells in the periphery. We also found a higher frequency of these cells in autoimmune-targeted organs with the occurrence of diabetes, suggesting their implication in the disease development. In humans, though absent in fresh PMBCs, iNKT17 cells are detected in vitro with a higher frequency in T1D patients compared to control subjects in the presence of the proinflammatory cytokine IL-1β, known to contribute to diabetes occurrence. These IL-1β-stimulated iNKT cells from T1D patients keep their potential to produce IFN-γ, a cytokine that drives islet β-cell destruction, but not IL-4, with a reverse picture observed in healthy volunteers. On the whole, our results argue in favour of a potential role of IL-17-producing iNKT cells in T1D and suggest that inflammation in T1D patients could induce a Th1/Th17 cytokine secretion profile in iNKT cells promoting disease development.

Oligoclonal expansions of mucosal T cells in Crohn's disease predominate in NKG2D-expressing CD4 T cells

Crohn's disease (CD) is an inflammatory pathology of the mucosal intestine that results from uncontrolled immune response towards commensal microbes. Clonal expansions of T cells have been found in patients with CD suggesting an antigen-specific stimulation of pathogenic T cells. Here we show, using T-cell receptor repertoire analysis by real-time PCR, that oligoclonal expansions are found in both CD8+ and CD4+ T cells in the blood and intestinal mucosa of CD patients. The majority of CD4+ T-cell-expanded clones are CD4+NKG2D+ T cells. These clonal expansions were found in both inflamed and neighboring healthy tissue and were persisting during the course of the disease. The presence of these CD4+NKG2D+ T-cell clones at the macroscopically normal edge of the surgical resection might be predictive of inflammation relapse post surgery.

Contribution of IL-17-producing gamma delta T cells to the efficacy of anticancer chemotherapy

IL-17 production by γδ T cells is required for tumor cell infiltration by IFN-γ–producing CD8⁺ T cells and inhibition of tumor growth in response to anthracyclines.

By triggering immunogenic cell death, some anticancer compounds, including anthracyclines and oxaliplatin, elicit tumor-specific, interferon-γ–producing CD8⁺ αβ T lymphocytes (Tc1 CTLs) that are pivotal for an optimal therapeutic outcome. Here, we demonstrate that chemotherapy induces a rapid and prominent invasion of interleukin (IL)-17–producing γδ (Vγ4⁺ and Vγ6⁺) T lymphocytes (γδ T17 cells) that precedes the accumulation of Tc1 CTLs within the tumor bed. In T cell receptor δ^−/− or Vγ4/6^−/− mice, the therapeutic efficacy of chemotherapy was compromised, no IL-17 was produced by tumor-infiltrating T cells, and Tc1 CTLs failed to invade the tumor after treatment. Although γδ T17 cells could produce both IL-17A and IL-22, the absence of a functional IL-17A–IL-17R pathway significantly reduced tumor-specific T cell responses elicited by tumor cell death, and the efficacy of chemotherapy in four independent transplantable tumor models. Adoptive transfer of γδ T cells restored the efficacy of chemotherapy in IL-17A^−/− hosts. The anticancer effect of infused γδ T cells was lost when they lacked either IL-1R1 or IL-17A. Conventional helper CD4⁺ αβ T cells failed to produce IL-17 after chemotherapy. We conclude that γδ T17 cells play a decisive role in chemotherapy-induced anticancer immune responses.

Cutting edge: crucial role of IL-1 and IL-23 in the innate IL-17 response of peripheral lymph node NK1.1- invariant NKT cells to bacteria

We have shown previously that peripheral lymph node-resident retinoic acid receptor-related orphan receptor γt(+) NK1.1(-) invariant NKT (iNKT) cells produce IL-17A independently of IL-6. In this study, we show that the concomitant presence of IL-1 and IL-23 is crucial to induce a rapid and sustained IL-17A/F and IL-22 response by these cells that requires TCR-CD1d interaction and partly relies on IL-23-mediated upregulation of IL-23R and IL-1R1 expression. We further show that IL-1 and IL-23 produced by pathogen-associated molecular pattern-stimulated dendritic cells induce this response from NK1.1(-) iNKT cells in vitro, involving mainly TLR2/4-signaling pathways. Finally, we found that IL-17A production by these cells occurs very early and transiently in vivo in response to heat-killed bacteria. Overall, our study indicates that peripheral lymph node NK1.1(-) iNKT cells could be a source of innate Th17-related cytokines during bacterial infections and supports the hypothesis that they are able to provide an efficient first line of defense against bacterial invasion.

Skin and peripheral lymph node invariant NKT cells are mainly retinoic acid receptor-related orphan receptor (gamma)t+ and respond preferentially under inflammatory conditions

Lymph nodes (LNs) have been long considered as comprising few invariant NKT (iNKT) cells, and these cells have not been studied extensively. In this study, we unravel the existence of stable rather than transitional LN-resident NK1.1(-) iNKT cell populations. We found the one resident in peripheral LNs (PLNs) to comprise a major IL-17-producing population and to express the retinoic acid receptor-related orphan receptor (gamma)t (ROR(gamma)t). These cells respond to their ligand alpha-galactosylceramide (alpha-GalCer) in vivo by expanding dramatically in the presence of LPS, providing insight into how this rare population could have an impact in immune responses to infection. PLN-resident ROR(gamma)t(+) NK1.1(-) iNKT cells express concomitantly CCR6, the integrin alpha-chain alpha(E) (CD103), and IL-1R type I (CD121a), indicating that they might play a role in inflamed epithelia. Accordingly, skin epithelia comprise a major ROR(gamma)t(+) CCR6(+)CD103(+)CD121a(+) NK1.1(-) cell population, reflecting iNKT cell composition in PLNs. Importantly, both skin and draining PLN ROR(gamma)t(+) iNKT cells respond preferentially to inflammatory signals and independently of IL-6, indicating that they could play a nonredundant role during inflammation. Overall, our study indicates that ROR(gamma)t(+) iNKT cells could play a major role in the skin during immune responses to infection and autoimmunity.

iNKT cell development is orchestrated by different branches of TGF-beta signaling

Invariant natural killer T (iNKT) cells constitute a distinct subset of T lymphocytes exhibiting important immune-regulatory functions. Although various steps of their differentiation have been well characterized, the factors controlling their development remain poorly documented. Here, we show that TGF-beta controls the differentiation program of iNKT cells. We demonstrate that TGF-beta signaling carefully and specifically orchestrates several steps of iNKT cell development. In vivo, this multifaceted role of TGF-beta involves the concerted action of different pathways of TGF-beta signaling. Whereas the Tif-1gamma branch controls lineage expansion, the Smad4 branch maintains the maturation stage that is initially repressed by a Tif-1gamma/Smad4-independent branch. Thus, these three different branches of TGF-beta signaling function in concert as complementary effectors, allowing TGF-beta to fine tune the iNKT cell differentiation program.

iNKT Cell-development is Orchestrated by Different Branches of TGF-beta Signaling (47.24)

iNKT cells constitute a distinct subset of T lymphocytes exhibiting important immune-regulatory functions. Although different steps of their differentiation have been well characterized, the factors controlling their development remain poorly documented. Here, we show that TGF-β controls the differentiation program of iNKT cells. We demonstrate that TGF-β signaling finely and specifically orchestrates several steps of iNKT cell development. In vivo this multifaceted role of TGF-β involves the concerted action of different pathways of TGF-β signaling. Whereas the Tif-1γ branch controls lineage expansion, the Smad4 branch maintains the maturation stage that is initially repressed by a Tif-1γ/Smad4-independent branch. Thus, these three different branches of TGF-β signaling function in concert as complementary effectors allowing TGF-β to finely tune the iNKT cell-differentiation program.

Influence of a non-NK complex region of chromosome 6 on CD4+ invariant NK T cell homeostasis

The number and function of immunoregulatory invariant NKT (iNKT) cells are genetically controlled. A defect of iNKT cell ontogeny and function has been implicated as one causal factor of NOD mouse susceptibility to type 1 diabetes. Other factors of diabetes susceptibility, such as a decrease of regulatory T cell function or an increase in TLR1 expression, are corrected in diabetes-resistant Idd6 NOD.C3H 6.VIII congenic mice. Thus, we surmised that the iNKT cell defects found in NOD mice may also be rescued in congenic mice. Unexpectedly, we found, in both the thymus and the periphery, a 50% reduction in iNKT cell number in NOD.C3H 6.VIII mice as compared with NOD mice. This reduction only affected CD4(+) iNKT cells, and left the double negative iNKT cells unchanged. In parallel, the production of IL-4 and IFN-gamma following alpha-GalCer stimulation was proportionally reduced. Using three subcongenic strains, we have narrowed down the region controlling iNKT development within Idd6 (5.8 Mb) to Idd6.2 region (2.5 Mb). Idd6 region had no effect on NK cell number and in vivo cytotoxic activity. These results indicate that the role of iNKT cells in diabetes development is equivocal and more complex than initially considered. In addition, they bring strong evidence that the regulation of CD4(+) iNKT cell production is independent from that of DN iNKT cells, and involves genes of the Idd6 locus.

Sensitivity of NK1.1-negative NKT cells to transgenic BATF defines a role for activator protein-1 in the expansion and maturation of immature NKT cells in the thymus

NKT cells are glycolipid-reactive lymphocytes that express markers and perform functions common to both T lymphocytes and NK cells. Although the genetic events controlling conventional T cell development are well defined, the transcription factors and genetic programs regulating NKT cell development are only beginning to be elucidated. Previously, we described the NKT cell-deficient phenotype of transgenic (Tg) mice constitutively expressing B cell-activating transcription factor (BATF), a basic leucine zipper protein and inhibitor of AP-1. In this study, we show that Tg BATF targets the majority of Valpha14Jalpha281 (Valpha14i(7)) NKT cells, regardless of CD4 expression and Vbeta gene usage. The residual NKT cells in the thymus of BATF-Tg mice are CD44(+), yet are slow to display the NK1.1 marker characteristic of mature cells. As a population, BATF-expressing NKT cells are TCRbeta/CD3epsilon(low), but express normal levels of CD69, suggesting a failure to expand appropriately following selection. Consistent with the sensitivity of NKT cells to BATF-induced changes in AP-1 activity, we detect a full complement of AP-1 basic leucine zipper proteins in wild-type NKT cells isolated from the thymus, spleen, and liver, and show that AP-1 DNA-binding activity and cytokine gene transcription are induced in NKT cells within a few hours of glycolipid Ag exposure. This study is the first to characterize AP-1 activity in NKT cells and implicates the integrity of this transcription factor complex in developmental events essential to the establishment of this unique T cell subset in the thymus.

Characterization of the early stages of thymic NKT cell development

Upon reaching the mature heat stable antigen (HSA)^low thymic developmental stage, CD1d-restricted Vα14-Jα18 thymocytes undergo a well-characterized sequence of expansion and differentiation steps that lead to the peripheral interleukin-4/interferon-γ–producing NKT phenotype. However, their more immature HSA^high precursors have remained elusive, and it has been difficult to determine unambiguously whether NKT cells originate from a CD4⁺CD8⁺ double-positive (DP) stage, and when the CD4⁺ and CD4⁻CD8⁻ double-negative (DN) NKT subsets are formed. Here, we have used a CD1d tetramer-based enrichment strategy to physically identify HSA^high precursors in thymuses of newborn mice, including an elusive DP^low stage and a CD4⁺ stage, which were present at a frequency of ∼10⁻⁶. These HSA^high DP and CD4⁺ stages appeared to be nondividing, and already exhibited the same Vβ8 bias that characterizes mature NKT cells. This implied that the massive expansion of NKT cells is separated temporally from positive selection, but faithfully amplifies the selected TCR repertoire. Furthermore, we found that, unlike the DN γδ T cells, the DN NKT cells did not originate from a pTα-independent pathway bypassing the DP stage, but instead were produced during a short window of time from the conversion of a fraction of HSA^low NK1.1^neg CD4 cells. These findings identify the HSA^high CD4⁺ stage as a potential branchpoint between NKT and conventional T lineages and between the CD4 and DN NKT sublineages.

Genetic evidence supporting selection of the Valpha14i NKT cell lineage from double-positive thymocyte precursors

Invariant Valpha14i NKT (iNKT) cells are a specialized subset of T lymphocytes with regulatory functions. They coexpress TCRalphabeta and natural killer cell markers. They differentiate through interaction of their Valpha14-Jalpha18 invariant TCRalpha chains with CD1d expressed on double-positive (DP) thymocytes. Although their development has been shown to be thymus dependent, their developmental pathway has not been definitively established. By using genetic analyses, we show here that all iNKT cells are selected from a pool of DP thymocytes. Their development is absolutely dependent on Runx1 and ROR(gamma)t, transcription factors that influence, but are not required for, development of conventional T cells. Our results indicate that even though CD1d binding DP thymocytes have yet to be observed, Valpha14-Jalpha18 rearrangement in these cells is required for development of iNKT cells.

Mechanisms governing B cell developmental defects in invariant chain-deficient mice

Invariant chain (Ii)-deficient mice exhibit profound B cell defects that have remained poorly understood, because they could not be simply explained by impaired Ag presentation. We found that Ii deficiency induced cell autonomous defects of two distinct B cell lineages. The life span of mature follicular (FO) B cells was reduced, accounting for their markedly decreased frequency, whereas, in contrast, marginal zone (MZ) B cells accumulated. Other Ii-expressing lineages such as B1 B cells and dendritic cells were unaffected. Surprisingly, the life span of FO B cells was fully corrected in Ii/I-Abeta doubly deficient mice, revealing that Ii-free I-Abeta chains alter FO B cell survival. In contrast, the accumulation of MZ B cells was controlled by a separate mechanism independent of I-Abeta. Interestingly, in Ii-deficient mice lacking FO B cells, the MZ B cells invaded the FO zone, suggesting that intact follicules contribute to the retention of B cells in the MZ. These findings reveal unexpected consequences of Ii deficiency on the development and organization of B cell follicles.

Editing of CD1d-bound lipid antigens by endosomal lipid transfer proteins

It is now established that CD1 molecules present lipid antigens to T cells, although it is not clear how the exchange of lipids between membrane compartments and the CD1 binding groove is assisted. We report that mice deficient in prosaposin, the precursor to a family of endosomal lipid transfer proteins (LTP), exhibit specific defects in CD1d-mediated antigen presentation and lack Valpha14 NKT cells. In vitro, saposins extracted monomeric lipids from membranes and from CD1, thereby promoting the loading as well as the editing of lipids on CD1. Transient complexes between CD1, lipid, and LTP suggested a "tug-of-war" model in which lipid exchange between CD1 and LTP is on the basis of their respective affinities for lipids. LTPs constitute a previously unknown link between lipid metabolism and immunity and are likely to exert a profound influence on the repertoire of self, tumor, and microbial lipid antigens.

T Cell Development in Mice Expressing CD1d Directed by a Classical MHC Class II Promoter

CD1d and nonclassical MHC molecules differ markedly from classical MHC ligands in their ability to promote the selection and differentiation of developing T cells. Whereas classical MHC-restricted T cells have a predominantly naive phenotype and a broad TCR repertoire, most other T cells have a memory and/or NKT phenotype with a restricted repertoire. Because the nonclassical ligands selecting these memory-type cells are expressed by bone marrow-derived cells, it has been suggested that the development of large repertoires of naive-type cells was dependent on the classical MHC expression pattern in the thymus cortex, high on epithelial cells and low on cortical thymocytes. We redirected CD1d expression using the classical MHC II Ealpha promoter. pEalpha-CD1d mice lacked memory-type NKT cells, but, surprisingly, they did not acquire the reciprocal ability to select a diverse population of naive CD1d-restricted cells. These findings suggest that, whereas the development of NKT cells is dependent on the pattern of CD1d expression, the absence of a broad, naive CD1d-restricted T cell repertoire may reflect intrinsic limitations of the pool of TCR genes or lipid Ags.

The paradox of immune molecular recognition of alpha-galactosylceramide: low affinity, low specificity for CD1d, high affinity for alpha beta TCRs

CD1 resembles both class I and class II MHC but differs by the important aspect of presenting lipid/glycolipids, instead of peptides, to T cells. Biophysical studies of lipid/CD1 interactions have been limited, and kinetics of binding are in contradiction with functional studies. We have revisited this issue by designing new assays to examine the loading of CD1 with lipids. As expected for hydrophobic interactions, binding affinity was not high and had limited specificity. Lipid critical micelle concentration set the limitation to these studies. Once loaded onto CD1d, the recognition of glycolipids by alphabeta T cell receptor was studied by surface plasmon resonance using soluble Valpha14-Vbeta8.2 T cell receptors. The Valpha14 Jalpha18 chain could be paired with NK1.1 cell-derived Vbeta chain, or any Vbeta8 chain, to achieve high affinity recognition of alpha-galactosylceramide. Biophysical analysis indicated little effect of temperature or ionic strength on the binding interaction, in contrast to what has been seen in peptide/MHC-TCR studies. This suggests that there is less accommodation made by this TCR in recognizing alpha-galactosylceramide, and it can be assumed that the most rigid part of the Ag, the sugar moiety, is critical in the interaction.

TGF-beta1 modulates Fas (APO-1/CD95)-mediated apoptosis of human pre-B cell lines

We have previously shown that Fas-induced apoptosis is markedly enhanced by IL-7 in human pre-B but not pro-B cell lines. In addition, pre-B cell receptor (pre-BCR) ligation significantly potentiates the IL-7 effects on Fas-triggered pre-B cell death. We show herein that transforming growth factor (TGF)-beta 1 sharply reduces Fas-induced death rate of pre-B but not pro-B cells. TGF-beta 1 causes inhibition of Fas-mediated disruption of mitochondrial transmembrane potential and cleavage of caspase 8, Bid and caspase 3. Bcl2 expression is markedly increased in TGF-beta 1-treated pre-B cells, whereas cellular FLICE-like inhibitory protein long (c-FLIPL), Bcl-XL, Bax, and Bad expression remains unchanged. TGF-beta 1 causes a selective growth arrest of pre-B cells in G0/G1 phase of the cell cycle and induces a partial down-modulation of both Fas and pre-BCR expression. All TGF-beta 1-mediated effects, but Bcl2 up-regulation, can be reproduced by the LY294002 phosphatidylinositol 3-kinase (PI3K)/Akt inhibitor but not by inhibitors of the MAPK/ERK (MEK) and Janus kinase (Jak)/STAT pathways, which promote cell death. Akt phosphorylation is strongly inhibited by TGF-beta1 in pre-B but not pro-B cells and is not modified by Fas engagement. Altogether, our findings suggest that TGF-beta1 prevents Fas-induced apoptosis of pre-B lines by inhibiting PI3K pathway and by enhancing expression of Bcl2. They also suggest that the PI3K/Akt pathway is involved in the control of Fas and pre-BCR expression, a checkpoint in B cell development.

Thymocyte expression of cathepsin L is essential for NKT cell development

CD1d antigen presentation to natural killer T (NKT) cells expressing the semi-invariant T cell receptor V(alpha)14J(alpha)18 requires CD1d trafficking through endosomal compartments; however, the endosomal events remain undefined. We show that mice lacking the endosomal protease cathepsin L (catL) have greatly reduced numbers of V(alpha)14(+)NK1.1(+) T cells. In addition, catL expression in thymocytes is critical not only for selection of these cells in vivo but also for stimulation of V(alpha)14(+)NK1.1(+) T cells in vitro. CD1d cell-surface expression and intracellular localization appear normal in catL-deficient thymocytes, as does the lysosomal morphology; this implies a specific role for catL in regulating presentation of natural CD1d ligands mediating V(alpha)14(+)NK1.1(+) T cell selection. These data implicate lysosomal proteases as key regulators of not only classical major histocompatibility complex class II antigen presentation but also nonclassical CD1d presentation.

Testing the NKT cell hypothesis of human IDDM pathogenesis

Defects in IL-4-producing CD1d-autoreactive NKT cells have been implicated in numerous Th1-mediated autoimmune diseases, including diabetes, multiple sclerosis, rheumatoid arthritis, lupus, and systemic sclerosis. Particular attention has been focused on autoimmune insulin-dependent diabetes mellitus (IDDM) because nonobese diabetic (NOD) mice and humans with IDDM are both reported to express severe deficiencies in the frequency and Th2 functions of NKT cells. Furthermore, experimental manipulations of the NKT defect in the NOD mouse induced corresponding changes in disease. Taken together, these converging studies suggested a general role of NKT cells in natural protection against destructive autoimmunity. However, in previous reports the identification of NKT cells was based on indirect methods. We have now devised a direct, highly specific CD1d tetramer-based methodology to test whether humans with IDDM have associated NKT cell defects. Surprisingly, although we find marked and stable differences in NKT cells between individuals, our study of IDDM patients and healthy controls, including discordant twin pairs, demonstrates that NKT cell frequency and IL-4 production are conserved during the course of IDDM. These results contradict previous conclusions and refute the hypothesis that NKT cell defects underlie most autoimmune diseases.

Testing the NKT cell hypothesis of human IDDM pathogenesis

Defects in IL-4-producing CD1d-autoreactive NKT cells have been implicated in numerous Th1-mediated autoimmune diseases, including diabetes, multiple sclerosis, rheumatoid arthritis, lupus, and systemic sclerosis. Particular attention has been focused on autoimmune insulin-dependent diabetes mellitus (IDDM) because nonobese diabetic (NOD) mice and humans with IDDM are both reported to express severe deficiencies in the frequency and Th2 functions of NKT cells. Furthermore, experimental manipulations of the NKT defect in the NOD mouse induced corresponding changes in disease. Taken together, these converging studies suggested a general role of NKT cells in natural protection against destructive autoimmunity. However, in previous reports the identification of NKT cells was based on indirect methods. We have now devised a direct, highly specific CD1d tetramer-based methodology to test whether humans with IDDM have associated NKT cell defects. Surprisingly, although we find marked and stable differences in NKT cells between individuals, our study of IDDM patients and healthy controls, including discordant twin pairs, demonstrates that NKT cell frequency and IL-4 production are conserved during the course of IDDM. These results contradict previous conclusions and refute the hypothesis that NKT cell defects underlie most autoimmune diseases.

A thymic precursor to the NK T cell lineage

CD1d-restricted autoreactive natural killer (NK1.1+) T cells function as regulatory cells in various disease conditions. Using improved tetramer tracking methodology, we identified a NK1.1- thymic precursor and followed its differentiation and emigration to tissues by direct cell transfer and in situ cell labeling studies. A major lineage expansion occurred within the thymus after positive selection and before NK receptor expression. Surprisingly, cytokine analysis of the developmental intermediates between NK and NK+ stages showed a T helper cell TH2 to TH1 conversion, suggesting that the regulatory functions of NK T cells may be developmentally controlled. These findings characterize novel thymic and postthymic developmental pathways that expand autoreactive cells and differentiate them into regulatory cells.

Distinct functional lineages of human V(alpha)24 natural killer T cells

CD1d-restricted autoreactive natural killer (NK)T cells have been reported to regulate a range of disease conditions, including type I diabetes and immune rejection of cancer, through the secretion of either T helper (Th)2 or Th1 cytokines. However, mechanisms underlying Th2 versus Th1 cytokine secretion by these cells are not well understood. Since most healthy subjects express <1 NKT cell per 1,000 peripheral blood lymphocytes (PBLs), we devised a new method based on the combined used of T cell receptor (TCR)-specific reagents alpha-galactosylceramide (alphaGalCer) loaded CD1d-tetramers and anti-V(alpha)24 monoclonal antibody, to specifically identify and characterize these rare cells in fresh PBLs. We report here that CD4(+) and CD4(-)CD8(-) (double negative [DN]) NKT cell subsets represent functionally distinct lineages with marked differences in their profile of cytokine secretion and pattern of expression of chemokine receptors, integrins, and NK receptors. CD4(+) NKT cells were the exclusive producers of interleukin (IL)-4 and IL-13 upon primary stimulation, whereas DN NKT cells had a strict Th1 profile and prominently expressed several NK lineage receptors. These findings may explain how NKT cells could promote Th2 responses in some conditions and Th1 in others, and should be taken into consideration for intervention in relevant diseases.

Multiple defects in antigen presentation and T cell development by mice expressing cytoplasmic tail-truncated CD1d

For members of the CD1 family of beta(2)-microglobulin-associated lipid-presenting molecules, tyrosine-based motifs in the cytoplasmic tail and invariant chain (Ii) govern glycoprotein trafficking through endosomal compartments. Little is known about the intracellular pathways of CD1 trafficking and antigen presentation. However, in vitro studies with cells transfected with mutant CD1 that had a truncated cytoplasmic tail have suggested a role for these tyrosine motifs in some, but not all, antigenic systems. By introducing a deletion of the tyrosine motif into the germ line, and through homologous recombination in embryonic stem cells, we now describe knock-in mice with the CD1d cytoplasmic tail deleted. Despite adequate surface CD1d expression and the presence of Ii, these mutant mice showed multiple and selective abnormalities in intracellular trafficking, antigen presentation and T cell development, demonstrating the critical functions of the CD1d cytoplasmic tail motif in vivo.

CD1d endosomal trafficking is independently regulated by an intrinsic CD1d-encoded tyrosine motif and by the invariant chain

Endosomal trafficking is an essential component of the CD1 pathway of lipid antigen presentation to T cells. We demonstrate that CD1d access to endosomal compartments is under dual regulation by an intrinsic tyrosine-based motif, which governs intense recycling between the plasma membrane and the endosome, and by the invariant chain, with which CD1d associates in the endoplasmic reticulum. Both pathways independently enhance antigen presentation to V(alpha)14(+) NKT cells, the main subset of CD1d-restricted T cells. These results reveal the complexity of CD1d trafficking and suggest that the invariant chain was a component of ancestral antigen presentation pathways prior to the evolution of MHC and CD1.

The mouse CD1d-restricted repertoire is dominated by a few autoreactive T cell receptor families

To define the phenotype and T cell receptor (TCR) repertoire of CD1d-dependent T cells, we compared the populations of T cells that persisted in major histocompatibility complex (MHC)-deficient mice, which lack mainstream T cells, with those from MHC/CD1d doubly deficient mice, which lack both mainstream and CD1d-dependent T cells. Surprisingly, up to 80% of the CD1d-dependent T cells were stained by tetramers of CD1d/alpha-galactosylceramide, which specifically identify the previously described CD1d autoreactive Valpha14-Jalpha18/Vbeta8 natural killer (NK) T cells. Furthermore, zooming in on the CD1d-dependent non-Valpha14 T cells, we found that, like Valpha14 NK T cells, they mainly expressed recurrent, CD1d autoreactive TCR families and had a natural memory phenotype. Thus, CD1d-restricted T cells differ profoundly from MHC-peptide-specific T cells by their predominant use of autoreactive and semiinvariant, rather than naive and diverse, TCRs. They more closely resemble other lineages of innate lymphocytes such as B-1 B cells, gammadelta T cells, and NK cells, which express invariant or semiinvariant autoreactive receptors. Finally, we demonstrate that the MHC-restricted TCR repertoire is essentially non-cross-reactive to CD1d. Altogether, these findings imply that lipid recognition by CD1d-restricted T cells may have largely evolved as an innate rather than an adaptive arm of the mouse immune system.

CD1d-restricted mouse V alpha 14 and human V alpha 24 T cells: lymphocytes of innate immunity

Mouse V alpha 14 T cells and their human homologs, V alpha 24 T cells, are prominent subsets of CD1d-restricted T cells. Here we discuss their striking similarities to B-1 B cells and gammadelta T cells and propose that these immune cells mediate various innate strategies in response to endogenous or exogenous danger signals.

In vivo identification of glycolipid antigen-specific T cells using fluorescent CD1d tetramers

The CD1 family of major histocompatibility complex (MHC)-like molecules specializes in presenting lipid and glycolipid antigens to alpha/beta T lymphocytes, but little is known about the size of the CD1-restricted T cell population or the frequency of T lymphocytes specific for a given glycolipid antigen. Here, we report the generation and use of mouse CD1d1-glycolipid tetramers to visualize CD1d-restricted T cells. In contrast with previous BIAcore-based estimates of very short half-lives for CD1d-glycolipid complexes, we found that the dissociation rate of several different CD1d-glycolipid complexes was very slow. Fluorescent tetramers of mouse CD1d1 complexed with alpha-galactosylceramide (alphaGalCer), the antigen recognized by mouse Valpha14-Jalpha281/Vbeta8 and human Valpha24-JalphaQ/Vbeta11 natural killer T (NKT) cell T cell receptors (TCRs), allowed us for the first time to accurately describe, based on TCR specificity, the entire population of NKT cells in vivo and to identify a previously unrecognized population of NK1.1-negative "NKT" cells, which expressed a different pattern of integrins. In contrast, natural killer (NK) cells failed to bind the tetramers either empty or loaded with alphaGalCer, suggesting the absence of a CD1d-specific, antigen-nonspecific NK receptor. Mouse CD1d1-alphaGalCer tetramers also stained human NKT cells, indicating that they will be useful for probing a range of mouse and human conditions such as insulin-dependent diabetes mellitus, tumor rejection, and infectious diseases where NKT cells play an important role.

Unaltered phenotype, tissue distribution and function of Valpha14(+) NKT cells in germ-free mice

The expression pattern of mouse CD1d and the tissue distribution of CD1d-restricted Valpha14-Jalpha281 NKT cells suggest that the liver and the marginal zone of the spleen might be preferred sites of activation of this potent innate pathway of early cytokine secretion. Because these tissues are particularly involved with the filtration of blood-borne pathogens, and because NKT cells with an activated / memory phenotype accumulate over the first weeks of life and their CD1 ligands bind microbial glycolipids, it has been hypothesized that expansion of the NKT cell subset may be driven by exposure to the microbial environment. To test this hypothesis, we analyzed the frequency, surface phenotype and functional properties of NKT cells in normal and in germ-free C57BL / 6 mice. Surprisingly, we found that the NKT cell subset develops in the presence or absence of a microbial environment. Although these results do not rule out the possibility that NKT cells exert a protective function against some microbial agents, they demonstrate that non microbial ligands, possibly self-antigens are sufficient for the generation, maturation and peripheral accumulation of NKT cells.

Unaltered phenotype, tissue distribution and function of Valpha14(+) NKT cells in germ-free mice

The expression pattern of mouse CD1d and the tissue distribution of CD1d-restricted Valpha14-Jalpha281 NKT cells suggest that the liver and the marginal zone of the spleen might be preferred sites of activation of this potent innate pathway of early cytokine secretion. Because these tissues are particularly involved with the filtration of blood-borne pathogens, and because NKT cells with an activated / memory phenotype accumulate over the first weeks of life and their CD1 ligands bind microbial glycolipids, it has been hypothesized that expansion of the NKT cell subset may be driven by exposure to the microbial environment. To test this hypothesis, we analyzed the frequency, surface phenotype and functional properties of NKT cells in normal and in germ-free C57BL / 6 mice. Surprisingly, we found that the NKT cell subset develops in the presence or absence of a microbial environment. Although these results do not rule out the possibility that NKT cells exert a protective function against some microbial agents, they demonstrate that non microbial ligands, possibly self-antigens are sufficient for the generation, maturation and peripheral accumulation of NKT cells.

Modifications of Igalpha and Igbeta expression as a function of B lineage differentiation

Transcription of the mb1 and B29 genes is initiated when lymphoid progenitors enter the B cell differentiation pathway, and their transmembrane Igalpha and Igbeta products constitute essential signaling components of pre-B and B cell antigen receptors. We analyzed Igalpha/Igbeta biosynthesis, heterogeneity, and molecular interactions as a function of human B lineage differentiation in cell lines representative of the pro-B, pre-B, and B cell stages. All B lineage representatives produced a 36-kDa Igbeta form and three principal Igalpha forms, transient 33/40-kDa species and a mature 44-kDa glycoprotein. Deglycosylation revealed a major Igalpha core protein of 25 kDa and a minor 21-kDa Igalpha protein, apparently the product of an alternatively spliced mRNA. In pro-B cells, the Igalpha and Igbeta molecules existed primarily in separate unassembled pools, exhibited an immature glycosylation pattern, did not associate with surrogate light chain proteins, and were retained intracellularly. Their unanticipated association with the Lyn protein-tyrosine kinase nevertheless suggests functional potential for the Igalpha/Igbeta molecules in pro-B cells. Greater heterogeneity of the Igalpha and Igbeta molecules in pre-B and B cell lines was attributable to increased glycosylation complexity. Finally, the Igalpha/Igbeta heterodimers associated with fully assembled IgM molecules as a terminal event in B cell receptor assembly.

IL-7 sensitizes human pre-B cells but not pro-B cells to Fas/APO-1 (CD95)-mediated apoptosis

Homeostasis of human B cell development is maintained by a complex network of cytoplasmic and surface expressed molecules. Abnormalities in this process may result in the expansion of malignant B cell precursors in B lineage acute lymphoblastic leukaemia (ALL). ALL cells share surface antigens with normal early precursor B cells. We have studied here the role of Fas/APO-1 (CD95) antigen on leukaemic precursor B cell line growth and survival, and the modulation of its effects by signals involved in normal early B cell development. Four ALL cell lines representative of the early steps of B cell differentiation are shown to express surface Fas/APO-1 (CD95) antigen and to undergo apoptosis in the presence of anti-Fas cross-linking antibodies. This effect is strongly enhanced when pre-B, but not pro-B cells, are pretreated with IL-7 but not with IL-2, IL-3, IL-4 or IL-10. Furthermore, pre-B cell death induced by anti-Fas antibodies in combination with IL-7 is increased upon pre-B receptor but not CD19 cross-linking. Bcl-2 and Bax protein expression is not influenced by IL-7 or pre-BR stimulation in either pro-B or pre-B cell lines. These results indicate that signals involved in normal early B cell development can modulate the Fas (CD95)-mediated apoptosis of leukaemic precursor B cells.

[Analysis of expression of the molecules Igalpha and Igbeta in human pro-B leukemic lines]

Ig alpha and Ig beta are two glycosylated transmembrane proteins of the Ig superfamily that are encoded by the B cell-specific genes mb-1 and B29, respectively. Ig alpha/Ig beta heterodimers may associate with the mu/surrogate light chains (psi LC) complex and with membrane Immunoglobulins on the surface of pre-B and B cells, respectively. They play a crucial role in the signal transduction that follows pre-B and B cell receptor cross-linking. Previous works have shown that mb-1 and B29 transcripts are expressed in normal mouse and human pro-B cells. However, little is known about the expression of Ig alpha and Ig beta molecules in pro-B cells. To address this issue we first analysed the expression of the Ig alpha and Ig beta molecules in the RS4; 11 and Nalm16 human pro-B cell lines using specific monoclonal antibodies. We found that both cell lines expressed Ig alpha and Ig beta but this expression was limited to the cytoplasm compartment. Three forms (44, 40 and 36 kDa) of the Ig alpha molecule and a single form (36 kDa) of the Ig beta molecule were detected in these lines. The heterogeneity of the Ig alpha molecule was partly related to the presence of a truncated Ig alpha protein which is likely the product of a short mb-1 transcript expressed in these cell lines. This short transcript is generated by alternative splicing of the mb1 mRNA with loss of exon 2. Ig alpha heterogeneity was also related to the expression of different glycosylated forms of the Ig alpha molecule. Only a minor fraction of the Ig alpha and Ig beta molecules associate with each other to form Ig alpha/Ig beta heterodimers and Ig beta homodimers. In these pro-B cell lines Ig alpha and Ig beta were found to associate with the lyn tyrosine kinase, suggesting that they may play some functional role at this B cell differentiation stage. Transfection of muHC gene in the Nalm16 cells results in the assembly of the pre-B receptor and in its expression on the cell surface. The level of surface expression of the pre-B receptor was found to correlate with the level of muHC and psi LC synthesis and with the level of association of the different components of the pre-B receptor with each other. Analysis of the 697 and Nalm6 pre-B cells and of the Ramos B cells indicated that heterogeneity of Ig alpha and Ig beta increases as a function of B cell differentiation.

Structural analysis of human antibodies to proteinase 3 from patients with Wegener granulomatosis

We determined the structure of five IgM autoAbs to proteinase-3 (PR3). These Abs are highly specific for Wegener's granulomatosis (WG) and may be involved in the pathogenesis of vasculitis in WG. Five clonal lymphoblastoid cell lines secreting Abs to PR3 were derived from four patients' B cells. From 3 to 5% of supernatants from wells contained detectable anti-PR3 Abs, indicating that anti-neutrophil cytoplasmic Ab specificity represents a sizable part of the IgM B cell repertoire in patients with WG. Mu heavy chains of WG1, WG4-1, and WG4-2 clones belonged to the VH3 subgroup. WG4-1 and WG4-2 heavy chains were identical, indicating an oligoclonal expansion of autoreactive B cells in this patient. WG4-1 (and WG4-2) used the VH3-23 V(H) gene, the product of which was shown to directly bind PR3. Heavy chains of WG2 and WG3 derived from VH4-59 and VH1-2 genes, respectively. Comparison with germline sequences showed that three of the five V(H) genes from clonal lines were somatically mutated with a R:S ratio in complementarity-determining regions of 3:0, 5:1, and 5:1, respectively. Three kappa light chains derived from the Vkappa4 gene, and one derived from a Vkappa1 gene. In these four Vkappa genes, there were overall R:S ratios of mutation of 8:1 and 0:7 in complementarity-determining regions and framework regions, respectively. These data suggest that the production of these autoantibodies, which are increasingly important in the diagnosis and management of WG, are influenced by an Ag-driven process.

Structural analysis of human antibodies to proteinase 3 from patients with Wegener granulomatosis

We determined the structure of five IgM autoAbs to proteinase-3 (PR3). These Abs are highly specific for Wegener's granulomatosis (WG) and may be involved in the pathogenesis of vasculitis in WG. Five clonal lymphoblastoid cell lines secreting Abs to PR3 were derived from four patients' B cells. From 3 to 5% of supernatants from wells contained detectable anti-PR3 Abs, indicating that anti-neutrophil cytoplasmic Ab specificity represents a sizable part of the IgM B cell repertoire in patients with WG. Mu heavy chains of WG1, WG4-1, and WG4-2 clones belonged to the VH3 subgroup. WG4-1 and WG4-2 heavy chains were identical, indicating an oligoclonal expansion of autoreactive B cells in this patient. WG4-1 (and WG4-2) used the VH3-23 V(H) gene, the product of which was shown to directly bind PR3. Heavy chains of WG2 and WG3 derived from VH4-59 and VH1-2 genes, respectively. Comparison with germline sequences showed that three of the five V(H) genes from clonal lines were somatically mutated with a R:S ratio in complementarity-determining regions of 3:0, 5:1, and 5:1, respectively. Three kappa light chains derived from the Vkappa4 gene, and one derived from a Vkappa1 gene. In these four Vkappa genes, there were overall R:S ratios of mutation of 8:1 and 0:7 in complementarity-determining regions and framework regions, respectively. These data suggest that the production of these autoantibodies, which are increasingly important in the diagnosis and management of WG, are influenced by an Ag-driven process.

Fate of surrogate light chains in B lineage cells

Biosynthesis of the immunoglobulin (Ig) receptor components and their assembly were examined in cell lines representative of early stages in human B lineage development. In pro-B cells, the nascent surrogate light chain proteins form a complex that transiently associates in the endoplasmic reticulum with a spectrum of unidentified proteins (40, 60, and 98 kD) and Bip, a heat shock protein family member. Lacking companion heavy chains, the surrogate light chains in pro-B cells do not associate with either the Ig(alpha) or Ig(beta) signal transduction units, undergo rapid degradation, and fail to reach the pro-B cell surface. In pre-B cells, by contrast, a significant portion of the surrogate light chain proteins associate with mu heavy chains, Ig(alpha), and Ig(beta) to form a stable receptor complex with a relatively long half-life. Early in this assembly process, Bip/GRP78, calnexin, GRP94, and a protein of approximately 17 kD differentially bind to the nascent mu heavy chains. The 17-kD intermediate is gradually replaced by the surrogate light chain protein complex, and the Ig(alpha) and Ig(beta) chains bind progressively to the mu heavy chains during the complex and relatively inefficient process of pre-B receptor assembly. The results suggest that, in humans, heavy chain association is essential for surrogate light chain survival and transport to the cell surface as an integral receptor component.