François Huetz

B cell depletion in immune thrombocytopenia reveals splenic long-lived plasma cells

Primary immune thrombocytopenia (ITP) is a disorder caused by autoantibody-mediated platelet destruction and decreased platelet production. Rituximab, a B cell-depleting agent, has become the first-line treatment for ITP; however, patients with refractory disease usually require splenectomy. We identified antibody-secreting cells as the major splenic B cell population that is resistant to rituximab. The phenotype, antibody specificity, and gene expression profile of these cells were characterized and compared to those of antibody-secreting cells from untreated ITP spleens and from healthy tissues. Antiplatelet-specific plasma cells (PC) were detected in the spleens of patients with ITP up to 6 months after rituximab treatment, and the PC population displayed a long-lived program similar to the one of bone marrow PC, thus explaining for most of these patients the absence of response to rituximab and the response to splenectomy. When analyzed by multiplex PCR at the single-cell level, normal splenic PC showed a markedly different gene expression profile, with an intermediate signature, including genes characteristic of both long-lived PC and proliferating plasmablasts. Surprisingly, long-lived PC were not detected in untreated ITP spleens. These results suggest that the milieu generated by B cell depletion promotes the differentiation and settlement of long-lived PC in the spleen.

Gfi-1B controls human erythroid and megakaryocytic differentiation by regulating TGF-β signaling at the bipotent erythro-megakaryocytic progenitor stage

Growth factor independence-1B (Gfi-1B) is a transcriptional repressor essential for erythropoiesis and megakaryopoiesis. Targeted gene disruption of GFI1B in mice leads to embryonic lethality resulting from failure to produce definitive erythrocytes, hindering the study of Gfi-1B function in adult hematopoiesis. We here show that, in humans, Gfi-1B controls the development of erythrocytes and megakaryocytes by regulating the proliferation and differentiation of bipotent erythro-megakaryocytic progenitors. We further identify in this cell population the type III transforming growth factor-beta receptor gene, TGFBR3, as a direct target of Gfi-1B. Knockdown of Gfi-1B results in altered transforming growth factor-beta (TGF-beta) signaling as shown by the increase in Smad2 phosphorylation and its inability to associate to the transcription intermediary factor 1-gamma (TIF1-gamma). Because the Smad2/TIF1-gamma complex is known to specifically regulate erythroid differentiation, we propose that, by repressing TGF-beta type III receptor (TbetaRIotaII) expression, Gfi-1B favors the Smad2/TIF1-gamma interaction downstream of TGF-beta signaling, allowing immature progenitors to differentiate toward the erythroid lineage.

IgM memory B cells: a mouse/human paradox

Humoral memory is maintained by two types of persistent cells, memory B cells and plasma cells, which have different phenotypes and functions. Long-lived plasma cells can survive for a lifespan within a complex niche in the bone marrow and provide continuous protective serum antibody levels. Memory B cells reside in secondary lymphoid organs, where they can be rapidly mobilized upon a new antigenic encounter. Surface IgG has long been taken as a surrogate marker for memory in the mouse. Recently, however, we have brought evidence for a long-lived IgM memory B cell population in the mouse, while we have also argued that, in humans, these same cells are not classical memory B cells but marginal zone (MZ) B cells which, as opposed to their mouse MZ counterpart, recirculate and carry a mutated B cell receptor. In this review, we will discuss these apparently paradoxical results.

Autoimmunity: the moving boundaries between physiology and pathology

Abstract This paper considers current concepts of autoimmunity and concludes with a discussion on the need for viable alternatives. It is argued that, if a century of ‘horror autotoxicus’ and over 30 years of active research based on ‘clonal deletion’ models have failed to contribute solutions to the problem, these notions are probably inadequate. Instead, it is proposed that pathological states of autoimmunity should be considered as deviations from normal autoreactivity which is a central property of the immune system. It follows that the study of autoimmune physiology is necessary to the understanding of pathology . Furthermore, the discrimination between destructive immune responses and physiological, self-directed immune activities is thought to be a systemic property based on a particular network organization, rather than the result of isolated clonal properties. These views suggest novel strategies in basic and clinical approaches to autoimmunity, more particularly the possibility of manipulating physiological autoreactivity to compensate diseases which are not of immunological origin.

IκBα/IκBε deficiency reveals that a critical NF-κB dosage is required for lymphocyte survival

In most cells, the NF-κB transcription factor is sequestered in the cytoplasm by interaction with inhibitory proteins, the IκBs. Here, we show that combined IκBα/IκBε deficiency in mice leads to neonatal death, elevated κB binding activity, overexpression of NF-κB target genes, and disruption of lymphocyte production. In IκBα/IκBε-deficient fetuses, B220+IgM+ B cells and single-positive T cells die by apoptosis. In adults, IκBα-/-IκBε-/- reconstituted chimeras exhibit a nearly complete absence of T and B cells that is not rescued by cotransfer with wild-type bone marrow. These findings demonstrate that IκBs tightly control NF-κB activity in vivo and that increased NF-κB activity intrinsically impairs lymphocyte survival. Because reduction or rise of NF-κB activity leads to similar dysfunction, they also reveal that only a narrow window of NF-κB activity is tolerated by lymphocytes.

VH-Gene Family Dominance in Ageing Mice

The cellular composition and Vn‐gene family repertoire were compared in different B‐cell compartments from young adult (8–12 weeks) and old (18–24 months) C57BL/6 and BALB/c mice. Ageing mice were found to have a higher frequency of peripheral mature B cells utilizing genes from a single VH‐gene family. While in each individual old C57BL/6 mice cells expressing the VH J558 gene family consistently were over‐represented, a marked individual variation was observed in old BALB/c mice with increased frequency of either the Vh J558, Q52 or J606 families. Aged mice were found also to have a reduced number of bone‐marrow pre‐B cells and an augmented number of splenic Ig‐secreting cells. These results suggest that old mice express less diversified antibody repertoires possibly as a consequence of reduced input from precursors and increased peripheral selection, which may be responsible for the progressive establishment of immunodeficiency.

Stimulation of B and T cells by in vivo high dose immunoglobulin administration in normal mice

Adult BALB/c mice were injected intravenously with a preparation of pooled normal murine IgG (400 mg/kg/day, on five consecutive days) and studied 8, 15, and 60 days later. High dose IgG administration increased the total numbers of splenic activated B and CD4+ (but not CD8+) T cells, as well as the numbers of splenic Ig-secreting cells, particularly in the IgG isotypes. Reactivities to some autoantigens, but not to bacterial or other heteroantigens, were selectively amplified amongst IgM-secreting cells. IgG administration did not alter the specific primary immune response to heterologous erythrocytes or bacterial dextran. No cellular alterations were detected in the lymph nodes or peritoneal cavity of treated animals. Most of these effects subsided with time, but some autoantibody reactivities remained elevated 60 days later. The present results suggest that the therapeutic effects of high dose IgG administration which have been reported in human diseases might be associated with the immunostimulatory activities of such treatment.

Natural variation in the parameters of innate immune cells is preferentially driven by genetic factors

The quantification and characterization of circulating immune cells provide key indicators of human health and disease. To identify the relative effects of environmental and genetic factors on variation in the parameters of innate and adaptive immune cells in homeostatic conditions, we combined standardized flow cytometry of blood leukocytes and genome-wide DNA genotyping of 1,000 healthy, unrelated people of Western European ancestry. We found that smoking, together with age, sex and latent infection with cytomegalovirus, were the main non-genetic factors that affected variation in parameters of human immune cells. Genome-wide association studies of 166 immunophenotypes identified 15 loci that showed enrichment for disease-associated variants. Finally, we demonstrated that the parameters of innate cells were more strongly controlled by genetic variation than were those of adaptive cells, which were driven by mainly environmental exposure. Our data establish a resource that will generate new hypotheses in immunology and highlight the role of innate immunity in susceptibility to common autoimmune diseases.Both environmental factors and genetic factors influence human immunity. Albert and colleagues leverage data from the Milieu Intérieur Consortium to comprehensively describe the effects of lifestyle, environment and genetics on human innate and adaptive immunity.

Waves of B-lymphopoiesis in the establishment of the mouse B-cell compartment.

In mouse, B-cell progenitors first become detectable in the embryonic body around day 9.5 of gestation in an unknown location, which is neither fetal liver nor peripheral blood [I]. Successive and/or superposed waves of lymphopoiesis then emerge in the embryo [2]. The pool of mature T lymphocytes is generated by the cyclic immigration of precursors to the thymus. where they are induced to differentiate fully, B-cell precursor immigration and commitment occurs in one wave in the etnbryonic avian bursa. and a synchronous wave of B cell development has also been characterized during a short temporal window (days 13-17 of gestation) in mouse fetal liver [3]. For many years, it has been admitted that all haemopoietic and lymphoid precursors formed in the yolk sac. Experimental data in avian embryos made il necessary to reconsider this view.

Loss of central and peripheral CD8+T‐cell tolerance to HFE in mouse models of human familial hemochromatosis

HFE, an MHC class Ib molecule that controls iron metabolism, can be directly targeted by cytotoxic TCR αβ T lymphocytes. Transgenic DBA/2 mice expressing, in a Rag 2 KO context, an αβ TCR that directly recognizes mouse HFE (mHFE) were created to further explore the interface of HFE with the immune system. TCR‐transgenic mHfe WT mice deleted mHFE‐reactive T cells in the thymus, but a fraction of reprogrammed cells were able to escape deletion. In contrast, TCR‐transgenic mice deprived of mHFE molecules (mHfe KO mice) or expressing a C282→Y mutated mHFE molecule – the most frequent mutation associated with human hereditary hemochromatosis – positively selected mHFE‐reactive CD8+ T lymphocytes and were not tolerant toward mHFE. By engrafting these mice with DBA/2 WT (mHFE+) skin, it was established, as suspected on the basis of similar engraftments performed on DBA/2 mHfe KO mice, that mHFE behaves as an autonomous skin‐associated histocompatibility antigen, even for mHFE‐C282→Y mutated mice. By contrast, infusion of DBA/2 mHFE+ mice with naïve mHFE‐reactive transgenic CD8+ T lymphocytes did not induce GVHD. Thus, tolerance toward HFE in mHfe WT mice can be acquired at either thymic or peripheral levels but is disrupted in mice reproducing human familial hemochromatosis.