Rosemarie H. DeKruyff

Pulmonary dendritic cells producing IL-10 mediate tolerance induced by respiratory exposure to antigen

Respiratory exposure to allergen induces T cell tolerance and protection against the development of airway hyperreactivity and asthma. However, the specific mechanisms by which tolerance is induced by respiratory allergen are not clear. We report here that pulmonary dendritic cells (DCs) from mice exposed to respiratory antigen transiently produced interleukin 10 (IL-10). These phenotypically mature pulmonary DCs, which were B-7hi as well as producing IL-10, stimulated the development of CD4+ T regulatory 1–like cells that also produced high amounts of IL-10. In addition, adoptive transfer of pulmonary DCs from IL-10+/+, but not IL-10−/−, mice exposed to respiratory antigen induced antigen-specific unresponsiveness in recipient mice. These studies show that IL-10 production by DCs is critical for the induction of tolerance, and that phenotypically mature pulmonary DCs mediate tolerance induced by respiratory exposure to antigen.

Antigen-specific regulatory T cells develop via the ICOS-ICOS-ligand pathway and inhibit allergen-induced airway hyperreactivity.

Asthma is caused by T-helper cell 2 (Th2)-driven immune responses, but the immunological mechanisms that protect against asthma development are poorly understood. T-cell tolerance, induced by respiratory exposure to allergen, can inhibit the development of airway hyperreactivity (AHR), a cardinal feature of asthma, and we show here that regulatory T (TR) cells can mediate this protective effect. Mature pulmonary dendritic cells in the bronchial lymph nodes of mice exposed to respiratory allergen induced the development of TR cells, in a process that required T-cell costimulation via the inducible costimulator (ICOS)–ICOS-ligand pathway. The TR cells produced IL-10, and had potent inhibitory activity; when adoptively transferred into sensitized mice,* TR cells blocked the development of AHR. Both the development and the inhibitory function of regulatory cells were dependent on the presence of IL-10 and on ICOS–ICOS-ligand interactions. These studies demonstrate that TR cells and the ICOS–ICOS-ligand signaling pathway are critically involved in respiratory tolerance and in downregulating pulmonary inflammation in asthma.*There was an error in the AOP version of this article. The sentence in the abstract that read The TR cells produced IL-10, and had potent inhibitory activity; when adoptively transferred into sensitized mouse TR cells, blocked the development of AHR was worded incorrectly. The following sentence is correct: The TR cells produced IL-10, and had potent inhibitory activity; when adoptively transferred into sensitized mice, TR cells blocked the development of AHR. This has been corrected in the HTML and the PDF. We regret this error.

Essential role of NKT cells producing IL-4 and IL-13 in the development of allergen-induced airway hyperreactivity

Using natural killer T (NKT) cell–deficient mice, we show here that allergen-induced airway hyperreactivity (AHR), a cardinal feature of asthma, does not develop in the absence of Vα14i NKT cells. The failure of NKT cell–deficient mice to develop AHR is not due to an inability of these mice to produce type 2 T-helper (Th2) responses because NKT cell–deficient mice that are immunized subcutaneously at non-mucosal sites produce normal Th2-biased responses. The failure to develop AHR can be reversed by the adoptive transfer of tetramer-purified NKT cells producing interleukin (IL)-4 and IL-13 to Ja281−/− mice, which lack the invariant T-cell receptor (TCR) of NKT cells, or by the administration to Cd1d−/− mice of recombinant IL-13, which directly affects airway smooth muscle cells. Thus, pulmonary Vα14i NKT cells crucially regulate the development of asthma and Th2-biased respiratory immunity against nominal exogenous antigens. Therapies that target Vα14i NKT cells may be clinically effective in limiting the development of AHR and asthma.

Allergen-specific Th1 cells fail to counterbalance Th2 cell–induced airway hyperreactivity but cause severe airway inflammation

Allergic asthma, which is present in as many as 10% of individuals in industrialized nations, is characterized by chronic airway inflammation and hyperreactivity induced by allergen-specific Th2 cells secreting interleukin-4 (IL-4) and IL-5. Because Th1 cells antagonize Th2 cell functions, it has been proposed that immune deviation toward Th1 can protect against asthma and allergies. Using an adoptive transfer system, we assessed the roles of Th1, Th2, and Th0 cells in a mouse model of asthma and examined the capacity of Th1 cells to counterbalance the proasthmatic effects of Th2 cells. Th1, Th2, and Th0 lines were generated from ovalbumin (OVA)-specific T-cell receptor (TCR) transgenic mice and transferred into lymphocyte-deficient, OVA-treated severe combined immunodeficiency (SCID) mice. OVA-specific Th2 and Th0 cells induced significant airway hyperreactivity and inflammation. Surprisingly, Th1 cells did not attenuate Th2 cell-induced airway hyperreactivity and inflammation in either SCID mice or in OVA-immunized immunocompetent BALB/c mice, but rather caused severe airway inflammation. These results indicate that antigen-specific Th1 cells may not protect or prevent Th2-mediated allergic disease, but rather may cause acute lung pathology. These findings have significant implications with regard to current therapeutic goals in asthma and allergy and suggest that conversion of Th2-dominated allergic inflammatory responses into Th1-dominated responses may lead to further problems.

Asthma: an epidemic of dysregulated immunity

The remarkable increase in asthma prevalence that has occurred over the last two decades is thought to be caused by changes in the environment due to improved hygiene and fewer childhood infections. However, the specific infections that limit T helper type 2 (TH2)-biased inflammation and asthma are not fully known. Infectious organisms, including commensal bacteria in the gastrointestinal tract and hepatitis A virus, may normally induce the development of regulatory T (TR) cells and protective immunity that limit airway inflammation and promote tolerance to respiratory allergens. In the absence of such infections, TH2 cells—which are developmentally related to TR cells—develop instead and coordinate the development of asthmatic inflammation.

Identification of Tapr (an airway hyperreactivity regulatory locus) and the linked Tim gene family

To simplify the analysis of asthma susceptibility genes located at human chromosome 5q23-35, we examined congenic mice that differed at the homologous chromosomal segment. We identified a Mendelian trait encoded by T cell and Airway Phenotype Regulator (Tapr). Tapr is genetically distinct from known cytokine genes and controls the development of airway hyperreactivity and T cell production of interleukin 4 (IL-4) and IL-13. Positional cloning identified a gene family that encodes T cell membrane proteins (TIMs); major sequence variants of this gene family (Tim) completely cosegregated with Tapr. The human homolog of TIM-1 is the hepatitis A virus (HAV) receptor, which may explain the inverse relationship between HAV infection and the development of atopy.

Critical Role for IL-13 in the Development of Allergen-Induced Airway Hyperreactivity

Airway hyperresponsiveness to a variety of specific and nonspecific stimuli is a cardinal feature of asthma, which affects nearly 10% of the population in industrialized countries. Eosinophilic pulmonary inflammation, eosinophil-derived products, as well as Th2 cytokines IL-13, IL-4, and IL-5, have been associated with the development of airway hyperreactivity (AHR), but the specific immunological basis underlying the development of AHR remains controversial. Herein we show that mice with targeted deletion of IL-13 failed to develop allergen-induced AHR, despite the presence of vigorous Th2-biased, eosinophilic pulmonary inflammation. However, AHR was restored in IL-13−/− mice by the administration of recombinant IL-13. Moreover, adoptive transfer of OVA-specific Th2 cells generated from TCR-transgenic IL-13−/− mice failed to induce AHR in recipient SCID mice, although such IL-13−/− Th2 cells produced high levels of IL-4 and IL-5 and induced significant airway inflammation. These studies definitively demonstrate that IL-13 is necessary and sufficient for the induction of AHR and that eosinophilic airway inflammation in the absence of IL-13 is inadequate for the induction of AHR. Therefore, treatment of human asthma with antagonists of IL-13 may be very effective.

The many paths to asthma: phenotype shaped by innate and adaptive immunity

Asthma is a very complex and heterogeneous disease that is characterized by airway inflammation and airway hyper-reactivity (AHR). The pathogenesis of asthma is associated with environmental factors, many cell types, and several molecular and cellular pathways. These include allergic, non-allergic and intrinsic pathways, which involve many cell types and cytokines. Animal models of asthma have helped to clarify some of the underlying mechanisms of asthma, demonstrating the importance of T helper type 2 (TH2)-driven allergic responses, as well as of the non-allergic and intrinsic pathways, and contributing to understanding of the heterogeneity of asthma. Further study of these many pathways to asthma will greatly increase understanding of the distinct asthma phenotypes, and such studies may lead to new therapies for this important public health problem.

The TIM gene family: emerging roles in immunity and disease

The search for cell-surface markers that can distinguish T helper 1 (TH1) cells from TH2 cells has led to the identification of a new gene family, encoding the T-cell immunoglobulin mucin (TIM) proteins, some of which are differentially expressed by TH1 and TH2 cells. The role of the TIM-family proteins in immune regulation is just beginning to emerge. Here, we describe the various TIM-family members in mice and humans, and discuss the genetic and functional evidence for their role in regulating autoimmune and allergic diseases.

Induction of T helper type 1-like regulatory cells that express Foxp3 and protect against airway hyper-reactivity.

The range of regulatory T cell (TR cell) types that control immune responses is poorly understood. We describe here a population of TR cells that developed in vivo from naive CD4+CD25− T cells during a T helper type 1 (TH1)–polarized response, distinct from CD25+ TR cells. These antigen-specific TR cells were induced by CD8α+ DCs, produced both interleukin 10 and interferon-γ, and potently inhibited the development of airway hyper-reactivity. These TR cells expressed the transcription factors Foxp3 and T-bet, indicating that these TR cells are related to TH1 cells. Thus, adaptive TR cells are heterogeneous and comprise TH1-like TR cells as well as previously described TH2-like TR cells, which express Foxp3 and are induced during the development of respiratory tolerance by CD8α− DCs.