Fred D. Finkelman

Local Macrophage Proliferation, Rather than Recruitment from the Blood, Is a Signature of TH2 Inflammation

Proliferation in situ, rather than immune cell recruitment, drives macrophage expansion in response to parasitic infection. A defining feature of inflammation is the accumulation of innate immune cells in the tissue that are thought to be recruited from the blood. We reveal that a distinct process exists in which tissue macrophages undergo rapid in situ proliferation in order to increase population density. This inflammatory mechanism occurred during T helper 2 (TH2)–related pathologies under the control of the archetypal TH2 cytokine interleukin-4 (IL-4) and was a fundamental component of TH2 inflammation because exogenous IL-4 was sufficient to drive accumulation of tissue macrophages through self-renewal. Thus, expansion of innate cells necessary for pathogen control or wound repair can occur without recruitment of potentially tissue-destructive inflammatory cells.

Interleukin‐4‐ and interleukin‐13‐mediated host protection against intestinal nematode parasites

Summary:  Intestinal worm infections characteristically induce T‐helper 2 cell (Th2) cytokine production. We reviewed studies performed with mice infected with either of two intestinal nematode parasites, Nippostrongylus brasiliensis or Trichinella spiralis, that evaluate the importance of the Th2 cytokine interleukin‐4 (IL‐4) and IL‐13 in protection against these parasites. These studies demonstrate that while IL‐4/IL‐13 protect against both parasites by activating signal transducer and activator of transcription 6 (Stat6) through IL‐4 receptor α (IL‐4Rα) ligation, Stat6 activation protects against these parasites through different mechanisms. Stat6‐dependent gene transcription promotes expulsion of N. brasiliensis solely through effects on non‐bone marrow‐derived cells that may include enhancement of intestinal smooth muscle contractility, changes in intestinal epithelial cell function, and increased intestinal mucus secretion. In contrast, Stat6 signaling promotes immunity to T. spiralis both through effects on bone marrow‐derived cells that can be reproduced by treating mice with IL‐4 or IL‐13 and through effects on non‐bone marrow‐derived cells. The former effects appear to include T‐cell‐dependent induction of intestinal mastocytosis, while the latter sensitize non‐bone marrow‐derived cells to mast cell‐produced mediators. We argue that a limited ability of the host immune system to distinguish among different nematode parasites has led to the evolution of a stereotyped Th2 response that activates a set of effector mechanisms that protects against most intestinal nematode parasites.

Basophils Produce IL-4 and Accumulate in Tissues after Infection with a Th2-inducing Parasite

Using mice in which the eGfp gene replaced the first exon of the Il4 gene (G4 mice), we examined production of interleukin (IL)-4 during infection by the intestinal nematode Nippostrongylus brasiliensis (Nb). Nb infection induced green fluorescent protein (GFP)pos cells that were FcɛRIpos, CD49bbright, c-kitneg, and Gr1neg. These cells had lobulated nuclei and granules characteristic of basophils. They were found mainly in the liver and lung, to a lesser degree in the spleen, but not in the lymph nodes. Although some liver basophils from naive mice express GFP, Nb infection enhanced GFP expression and increased the number of tissue basophils. Similar basophil GFP expression was found in infected Stat6−/− mice. Basophils did not increase in number in infected Rag2−/− mice; Rag2−/− mice reconstituted with CD4 T cells allowed significant basophil accumulation, indicating that CD4 T cells can direct both tissue migration of basophils and enhanced IL-4 production. IL-4 production was immunoglobulin independent and only partially dependent on IL-3. Thus, infection with a parasite that induces a “Th2-type response” resulted in accumulation of tissue basophils, and these cells, stimulated by a non-FcR cross-linking mechanism, are a principal source of in vivo IL-4 production.

The importance of Th2 cytokines in protective immunity to nematodes

The immune response is characterized by its high degree of specificity. B lymphocytes capable of producing antibodies that react with an antigen are selected to proliferate and to difierentiate as a result of their binding antigens that are directly stimulatory (Moller 1975) and as a result of their presentation of antigens to antigen-specific helper T lymphocytes (Noelle & Snow 1991). T lymphocytes similarly are selected to proliferate and to differentiate as a result of signals received when they are presented with an antigen-derived peptide/self MHC complex by antigen-presenting cells, such as B lymphocytes, dendritic cells or macrophages (Lanzavecchia 1990). Specificity of the immune response is maintained because only those lymphocytes that are capable of reacting with a determinant on the immunogen are induced to clonally expand and differentiate into mature effector cells. There is, however, a second, less completely understood aspect to immune specificity. Different effector mechanisms are recruited in response to different antigens or pathogens. In the mouse, for example, viral infections typically induce antibody responses of the IgG2a isotype (Coutelier et al. 1987), and are accompanied by activation of macrophages and the generation of cytotoxic T lymphocytes (Leist et al. 1989). In contrast, helminth parasites typically

Intestinal nematode parasites, cytokines and effector mechanisms

Laboratory models of intestinal nematode infection have played an important role in developing our understanding of the immune mechanisms that operate against infectious agents. The type of helper T cell response that develops following infection with intestinal nematode parasites is critical to the outcome of infection. The early events that mediate polarisation of the helper T cell subsets towards either Th1 or Th2 during intestinal nematode infection are not well characterised, but it is likely that multiple factors influence the induction of a Th1 or Th2 type response, just as multiple effector mechanisms are involved in worm expulsion. Costimulatory molecules have been shown to be important in driving T helper cell development down a specific pathway as has the immediate cytokine environment during T cell activation. If helper T cells of the Th2 type gain ascendancy then a protective immune response ensues, mediated by Th2 type cytokines and the effector mechanisms they control. In contrast, if an inappropriate Th1 type response predominates the ability to expel infection is compromised. Equally important is the observation that multiple potential effector mechanisms are stimulated by nematode infection, with a unique combination operating against the parasite depending on nematode species and its life cycle stage. Despite the close association between intestinal nematode infection and the generation of eosinophilia, mastocytosis and IgE it has been difficult to consistently demonstrate a role for these effector cells/molecules in resistance to nematode parasites, although mast cells are clearly important in some cases. It therefore seems that, in general, less classical Th2 controlled effector mechanisms, which remain poorly defined, are probably important in resistance to nematode parasites. Thus, our understanding of both the induction and effector phases remains incomplete and will remain an intense area of interest in the coming years.

Importance of Cytokines in Murine Allergic Airway Disease and Human Asthma

Asthma is a common, disabling inflammatory respiratory disease that has increased in frequency and severity in developed nations. We review studies of murine allergic airway disease (MAAD) and human asthma that evaluate the importance of Th2 cytokines, Th2 response-promoting cytokines, IL-17, and proinflammatory and anti-inflammatory cytokines in MAAD and human asthma. We discuss murine studies that directly stimulate airways with specific cytokines or delete, inactivate, neutralize, or block specific cytokines or their receptors, as well as controversial issues including the roles of IL-5, IL-17, and IL-13Rα2 in MAAD and IL-4Rα expression by specific cell types. Studies of human asthmatic cytokine gene and protein expression, linkage of cytokine polymorphisms to asthma, cytokine responses to allergen stimulation, and clinical responses to cytokine antagonists are discussed as well. Results of these analyses establish the importance of specific cytokines in MAAD and human asthma and have therapeutic implications.

IgG-blocking antibodies inhibit IgE-mediated anaphylaxis in vivo through both antigen interception and FcγRIIb cross-linking

Although it has long been hypothesized that allergen immunotherapy inhibits allergy, in part, by inducing production of IgG Abs that intercept allergens before they can cross-link mast cell Fc epsilonRI-associated IgE, this blocking Ab hypothesis has never been tested in vivo. In addition, evidence that IgG-allergen interactions can induce anaphylaxis by activating macrophages through Fc gammaRIII suggested that IgG Ab might not be able to inhibit IgE-mediated anaphylaxis without inducing anaphylaxis through this alternative pathway. We have studied active and passive immunization models in mice to approach these issues and to determine whether any inhibition of anaphylaxis observed was a direct effect of allergen neutralization by IgG Ab or an indirect effect of cross-linking of Fc epsilonRI to the inhibitory IgG receptor Fc gammaRIIb. We demonstrate that IgG Ab produced during the course of an immune response or administered passively can completely suppress IgE-mediated anaphylaxis; that these IgG blocking Abs inhibit IgE-mediated anaphylaxis without inducing Fc gammaRIII-mediated anaphylaxis only when IgG Ab concentration is high and challenge allergen dose is low; that allergen epitope density correlates inversely with the allergen dose required to induce both IgE- and Fc gammaRIII-mediated anaphylaxis; and that both allergen interception and Fc gammaRIIb-dependent inhibition contribute to in vivo blocking Ab activity.

Anti-inflammatory activity of IgG1 mediated by Fc galactosylation and association of FcγRIIB and dectin-1

Complement is an ancient danger-sensing system that contributes to host defense, immune surveillance and homeostasis. C5a and its G protein–coupled receptor mediate many of the proinflammatory properties of complement. Despite the key role of C5a in allergic asthma, autoimmune arthritis, sepsis and cancer, knowledge about its regulation is limited. Here we demonstrate that IgG1 immune complexes (ICs), the inhibitory IgG receptor FcγRIIB and the C-type lectin–like receptor dectin-1 suppress C5a receptor (C5aR) functions. IgG1 ICs promote the association of FcγRIIB with dectin-1, resulting in phosphorylation of Src homology 2 domain–containing inositol phosphatase (SHIP) downstream of FcγRIIB and spleen tyrosine kinase downstream of dectin-1. This pathway blocks C5aR-mediated ERK1/2 phosphorylation, C5a effector functions in vitro and C5a-dependent inflammatory responses in vivo, including peritonitis and skin blisters in experimental epidermolysis bullosa acquisita. Notably, high galactosylation of IgG N-glycans is crucial for this inhibitory property of IgG1 ICs, as it promotes the association between FcγRIIB and dectin-1. Thus, galactosylated IgG1 and FcγRIIB exert anti-inflammatory properties beyond their impact on activating FcγRs.

Foxa2 regulates alveolarization and goblet cell hyperplasia

The airways are lined by several distinct epithelial cells that play unique roles in pulmonary homeostasis; however, the mechanisms controlling their differentiation in health and disease are poorly understood. The winged helix transcription factor, FOXA2, is expressed in the foregut endoderm and in subsets of respiratory epithelial cells in the fetal and adult lung. Because targeted mutagenesis of the Foxa2 gene in mice is lethal before formation of the lung, its potential role in lung morphogenesis and homeostasis has not been determined. We selectively deleted Foxa2 in respiratory epithelial cells in the developing mouse lung. Airspace enlargement, goblet cell hyperplasia, increased mucin and neutrophilic infiltration were observed in lungs of the Foxa2-deleted mice. Experimental goblet cell hyperplasia caused by ovalbumin sensitization, interleukin 4 (IL4), IL13 and targeted deletion of the gene encoding surfactant protein C (SP-C), was associated with either absent or decreased expression of Foxa2 in airway epithelial cells. Analysis of lung tissue from patients with a variety of pulmonary diseases revealed a strong inverse correlation between FOXA2 and goblet cell hyperplasia. FOXA2 is required for alveolarization and regulates airway epithelial cell differentiation in the postnatal lung.

The Impact of T Helper and T Regulatory Cells on the Regulation of Anti-Double-Stranded DNA B Cells

Autoreactive B cells that appear to be inactivated can be found in healthy individuals. In this study, we examined the potential of these anergic cells to become activated. We show that anergy of anti-double-stranded DNA (dsDNA) B cells in BALB/c mice is readily reversed, requiring only the provision of T cell help. We further show that spontaneous loss of anergy among anti-dsDNA B cells in autoimmune lpr/lpr mice occurs in two phases: an abortive initial response to T help followed by full loss of tolerance. Strikingly, the abortive response can be reproduced in nonautoimmune mice when CD4+CD25+ T regulatory cells are administered in conjunction with CD4+ T helper cells, suggesting that loss of B cell tolerance may require both the production of T cell help and the overcoming of T suppression.