David F. LaRosa

Commensal bacteria-derived signals regulate basophil hematopoiesis and allergic inflammation

Commensal bacteria that colonize mammalian barrier surfaces are reported to influence T helper type 2 (TH2) cytokine-dependent inflammation and susceptibility to allergic disease, although the mechanisms that underlie these observations are poorly understood. In this report, we find that deliberate alteration of commensal bacterial populations via oral antibiotic treatment resulted in elevated serum IgE concentrations, increased steady-state circulating basophil populations and exaggerated basophil-mediated TH2 cell responses and allergic inflammation. Elevated serum IgE levels correlated with increased circulating basophil populations in mice and subjects with hyperimmunoglobulinemia E syndrome. Furthermore, B cell–intrinsic expression of myeloid differentiation factor 88 (MyD88) was required to limit serum IgE concentrations and circulating basophil populations in mice. Commensal-derived signals were found to influence basophil development by limiting proliferation of bone marrow–resident precursor populations. Collectively, these results identify a previously unrecognized pathway through which commensal-derived signals influence basophil hematopoiesis and susceptibility to TH2 cytokine–dependent inflammation and allergic disease.

The Innate Immune System in Allograft Rejection and Tolerance

As T cells alone are both necessary and sufficient for the rejection of virtually all allogeneic tissues, much of transplantation immunology has focused on cells of the adaptive immune system. During the past decade, advances in our understanding of innate responses to pathogen-associated molecules have spurred a “rediscovery” of innate immunity. Fueled by this, an increasing body of literature has emerged in which the role of the innate immune system in allograft rejection and tolerance has been examined more closely. This review will give an overview of recent studies and emerging concepts of how the cellular components of the innate immune system participate in the immune response to solid organ transplantation. These important studies highlight the complex interplay between diverse cells of the immune response and provide the basis for optimal strategies of tolerance induction.

Mechanisms Underlying Blockade of Allograft Acceptance by TLR Ligands

Immune activation via TLRs is known to prevent transplantation tolerance in multiple animal models. To investigate the mechanisms underlying this barrier to tolerance induction, we used complementary murine models of skin and cardiac transplantation in which prolonged allograft acceptance is either spontaneous or pharmacologically induced with anti-CD154 mAb and rapamycin. In each model, we found that prolonged allograft survival requires the presence of natural CD4+Foxp3+ T regulatory cells (Tregs), and that the TLR9 ligand CpG prevents graft acceptance both by interfering with natural Treg function and by promoting the differentiation of Th1 effector T cells in vivo. We further demonstrate that although Th17 cells differentiate from naive alloreactive T cells, these cells do not arise from natural Tregs in either CpG-treated or untreated graft recipients. Finally, we show that CpG impairs natural Treg suppressor capability and prevents Treg-dependent allograft acceptance in an IL-6-independent fashion. Our data therefore suggest that TLR signals do not prevent prolonged graft acceptance by directing natural Tregs into the Th17 lineage or by using other IL-6-dependent mechanisms. Instead, graft destruction results from the ability of CpG to drive Th1 differentiation and interfere with immunoregulation established by alloreactive natural CD4+Foxp3+ Tregs.

T cell expression of MyD88 is required for resistance to Toxoplasma gondii

Resistance to Toxoplasma gondii depends on dendritic cells to recognize this pathogen and secrete IL-12, in turn promoting IFN-γ production from responding T cells. The adaptor protein, myeloid differentiation primary-response gene 88 (MyD88), is important for most Toll-like receptor (TLR) signaling, as well as IL-1R/IL-18R signals. There is considerable evidence that MyD88 is required for the innate sensing of T. gondii and IL-12 responses. Although Myd88−/− mice challenged with T. gondii have defective IL-12 and Th1 effector responses and succumb to disease, administration of IL-12 to Myd88−/− mice partially restores the Th1 response and yet fails to prolong survival. This finding suggested that MyD88 may mediate signals within T cells important for resistance to this pathogen. To evaluate the role of MyD88 in T cells under noncompetitive conditions, bone marrow chimeras were generated, in which the T cells lacked MyD88, but MyD88-dependent innate immune responses were intact. Upon challenge with T. gondii, these chimeric mice were more susceptible to disease, developing severe toxoplasmic encephalitis and succumbing within 30 days. Splenocytes and brain mononuclear cells isolated from infected chimeric mice produced less IFN-γ when cultured with a T. gondii-derived antigen. The increase in susceptibility observed was independent of signals via the IL-1R and IL-18R, suggesting a role for TLRs in MyD88-mediated T cell responses to T. gondii. These observations show that, in addition to a role for MyD88 in innate responses, T cell expression of MyD88 is necessary for prolonged resistance to a pathogen.

MyD88 Plays a Critical T Cell-Intrinsic Role in Supporting CD8 T Cell Expansion during Acute Lymphocytic Choriomeningitis Virus Infection

During acute lymphocytic choriomeningitis virus (LCMV) infection, CD8 T cells rapidly expand and differentiate into effectors that are required for viral clearance. The accumulation of activated T cells is greatly reduced in mice lacking the adaptor molecule MyD88. Although MyD88 has generally been considered to indirectly regulate adaptive immune responses by controlling inflammatory cytokine production and Ag presentation in innate immune cells, in this study, we identify an unappreciated cell-intrinsic role for MyD88 in LCMV-specific CD8 T cells. Using reciprocal adoptive transfer models and bone marrow chimeras, we show that Myd88−/− CD8 T cells are defective in their clonal expansion in response to LCMV infection, independent of their environment. Furthermore, we show that while MyD88 is dispensable for initial activation and division of LCMV-specific CD8 T cells during the early stages of viral infection, MyD88-dependent signals are critical for supporting their survival and sustained accumulation.

Presentation of Toxoplasma gondii Antigens via the Endogenous Major Histocompatibility Complex Class I Pathway in Nonprofessional and Professional Antigen-Presenting Cells

ABSTRACT Challenge with the intracellular protozoan parasite Toxoplasma gondii induces a potent CD8+ T-cell response that is required for resistance to infection, but many questions remain about the factors that regulate the presentation of major histocompatibility complex class I (MHC-I)-restricted parasite antigens and about the role of professional and nonprofessional accessory cells. In order to address these issues, transgenic parasites expressing ovalbumin (OVA), reagents that track OVA/MHC-I presentation, and OVA-specific CD8+ T cells were exploited to compare the abilities of different infected cell types to stimulate CD8+ T cells and to define the factors that contribute to antigen processing. These studies reveal that a variety of infected cell types, including hematopoietic and nonhematopoietic cells, are capable of activating an OVA-specific CD8+ T-cell hybridoma, and that this phenomenon is dependent on the transporter associated with antigen processing and requires live T. gondii. Several experimental approaches indicate that T-cell activation is a consequence of direct presentation by infected host cells rather than cross-presentation. Surprisingly, nonprofessional antigen-presenting cells (APCs) were at least as efficient as dendritic cells at activating this MHC-I-restricted response. Studies to assess whether these cells are involved in initiation of the CD8+ T-cell response to T. gondii in vivo show that chimeric mice expressing MHC-I only in nonhematopoietic compartments are able to activate OVA-specific CD8+ T cells upon challenge. These findings associate nonprofessional APCs with the initial activation of CD8+ T cells during toxoplasmosis.

Granulomatous-lymphocytic interstitial lung disease associated with common variable immunodeficiency: CT findings.

Purpose To evaluate computed tomography (CT) scans of individuals with granulomatous-lymphocytic interstitial lung disease and common variable immunodeficiency (CVID) to determine if there are imaging features that distinguish this manifestation of CVID from the more usual imaging findings. Materials and Methods A review of the CVID population at our institution identified a series of 5 patients with CVID who had documented granulomatous disease on biopsy specimens. The initial and follow-up CT examinations were reviewed by 2 radiologists, and imaging findings in the chest and abdomen were tabulated by consensus. In addition, a pathologist reviewed histopathologic specimens and clinical presentations and therapeutic interventions were obtained from patient charts. Results In all, 5/5 patients (100%) had widespread pulmonary micronodules with a lower lung zone predominance, 4/5 (80%) had smooth interlobular septal thickening with mid to lower lung zone predominance, 1/5 (20%) had mild bronchiectasis, 4/5 (80%) had multifocal pulmonary consolidation, 5/5 (100%) had thoracic or abdominal lymphadenopathy, 2/5 (40%) had hepatomegaly, 5/5 (100%) had splenomegaly, 1/5 (20%) had nonspecific hypoattenuating splenic lesions, and 2/5 (40%) had nonspecific hypoattenuating renal lesions. The pulmonary nodules and lymphadenopathy commonly tended to wax and wane in severity over time, and more marked disease was often associated with areas of focal consolidation. Conclusion Granulomatous-lymphocytic interstitial lung disease, which can occur in patients with CVID, presents with CT findings distinct from the usual airway abnormalities most commonly associated with CVID.

Cooperation of adapter molecules in proximal signaling cascades during allergic inflammation

Summary:  Activation of mast cells through their high‐affinity immunoglobulin E receptor (FcεRI) plays an important role in allergic disorders. Other mast cell‐activating stimuli, such as Toll‐like receptor (TLR) ligands, synergize with FcεRI to enhance allergic inflammation. Thus, there is much interest in understanding how signaling occurs downstream of these receptors. One key event for FcεRI‐mediated mast cell activation is the inducible formation of multimolecular proximal signaling complexes. These complexes are nucleated by adapter proteins, scaffolds that localize various signaling molecules through their multiple molecule‐binding domains. Here we review recent findings in proximal signaling cascades with an emphasis on how adapter molecules cooperate with each other to generate an optimal signal in mast cells, and we discuss how signals crosstalk between FcεRI and TLRs in enhancing mast cell activation. Deciphering the molecular mechanisms leading to mast cell activation will hopefully bring new ideas for the development of novel therapeutics to control allergic diseases.

Constitutive Activation of STAT5 Supersedes the Requirement for Cytokine and TCR Engagement of CD4+ T Cells in Steady-State Homeostasis

The transcription factor STAT5 is one of several signaling mediators activated via common γ-chain cytokine receptors. As such, it plays an important role in lymphocyte survival and proliferation during normal homeostasis as well as under lymphopenic conditions. Transgenic mice expressing a constitutively activated form of STAT5b have been shown previously to contain increased numbers of peripheral CD4+CD25− T cells. To define the mechanism(s) for this occurrence, we have used adoptive transfer studies to examine the effects of STAT5 activity on steady-state CD4+ T cell homeostasis. We observed that constitutive STAT5 signaling induced 4- to 7-fold increased levels of basal steady-state proliferation, which was accompanied by a comparable increase in T cell recovery. Most strikingly, steady-state CD4 T cell proliferation occurred independently of both MHC class II and IL-15. These observations demonstrate that the STAT5-driven pathway is important to lymphocyte homeostasis and can supersede the need for both TCR engagement and cytokine stimulation. This suggests that the need for TCR stimulation to induce common γ-chain cytokine receptor expression, and thus STAT5 activation, is a key factor in maintaining normal CD4+ T cell homeostasis.

IL-10-induced gp130 expression in mouse mast cells permits IL-6 trans-signaling

It is reported that human and mouse mast cells express the IL‐27R, which consists of WSX‐1 (the IL‐27Rα subunit) and the signal‐transducing subunit gp130. Although it has been proposed that IL‐27 may negatively regulate mast cell‐dependent, immediate hypersensitivity responses directly, this has yet to be examined specifically. We found that mouse BMMC and primary peritoneal mast cells are unresponsive to IL‐27. Consistent with this, gp130 protein in resting BMMC was not on the cell surface to a measurable degree but was found intracellularly, and data are consistent with incompletely processed N‐linked glycosylation. Furthermore, BMMC constitutively expressed SOCS3, a major negative regulator of gp130 signaling. However, BMMC stimulation with IL‐10 and consequential STAT3 activation increased gp130 expression, which resulted in a functional gp130 receptor on the BMMC cell surface. IL‐10 has not been previously shown to regulate gp130 expression, which on the BMMC surface, permitted IL‐6 trans‐signaling, found to increase survival under limiting conditions and enhance IL‐13 and TNF‐α secretion. This study identifies factors that regulate mouse mast cell gp130 expression and signaling and makes conspicuous the limitations of using cultured mouse mast cells to study the effects of the IL‐6/IL‐12 cytokine family on mast cell biology.