The leukotriene C(4) transporter MRP1 regulates CCL19 (MIP-3beta, ELC)-dependent mobilization of dendritic cells to lymph nodes

Adaptive immune responses begin after antigen-bearing dendritic cells (DCs) traffic from peripheral tissues to lymph nodes. Here, we show that DC migration from skin to lymph nodes utilizes the leukotriene C(4) (LTC(4)) transporter multidrug resistance-associated protein 1 (MRP1). DC mobilization from the epidermis and trafficking into lymphatic vessels was greatly reduced in MRP1(-/-) mice, but migration was restored by exogenous cysteinyl leukotrienes LTC(4) or LTD(4). In vitro, these cysteinyl leukotrienes promoted optimal chemotaxis to the chemokine CCL19, but not to other related chemokines. Antagonism of CCL19 in vivo prevented DC migration out of the epidermis. Thus, MRP-1 regulates DC migration to lymph nodes, apparently by transporting LTC(4), which in turn promotes chemotaxis to CCL19 and mobilization of DCs from the epidermis.     

Chemokines and chemokine receptors expression in the lesions of patients with American cutaneous leishmaniasis

American cutaneous leishmaniasis (ACL) presents distinct active clinical forms with different grades of severity, known as localised (LCL), intermediate (ICL) and diffuse (DCL) cutaneous leishmaniasis. LCL and DCL are associated with a polarised T-helper (Th)1 and Th2 immune response, respectively, whereas ICL, or chronic cutaneous leishmaniasis, is associated with an exacerbated immune response and a mixed cytokine expression profile. Chemokines and chemokine receptors are involved in cellular migration and are critical in the inflammatory response. Therefore, we evaluated the expression of the chemokines CXCL10, CCL4, CCL8, CCL11 and CXCL8 and the chemokine receptors CCR3, CXCR3, CCR5 and CCR7 in the lesions of patients with different clinical forms of ACL using immunohistochemistry. LCL patients exhibited a high density of CXCL10+, CCL4+ and CCL8+ cells, indicating an important role for these chemokines in the local Th1 immune response and the migration of CXCR3+ cells. LCL patients showed a higher density of CCR7+ cells than ICL or DCL patients, suggesting major dendritic cell (DC) migration to lymph nodes. Furthermore, DCL was associated with low expression levels of Th1-associated chemokines and CCL11+ epidermal DCs, which contribute to the recruitment of CCR3+ cells. Our findings also suggest an important role for epidermal cells in the induction of skin immune responses through the production of chemokines, such as CXCL10, by keratinocytes.     

In vitro infection of human dendritic cells by Aspergillus fumigatus conidia triggers the secretion of chemokines for neutrophil and Th1 lymphocyte recruitment

Given the role played by chemokines in the selective homing of immune cells, we sought to characterize the profile of chemokines produced by human dendritic cells (DC) following in vitro Aspergillus fumigatus infection and their ability to recruit cells involved in the antifungal defense. At the onset of A. fumigatus infection, DC released elevated amounts of CXCL8 that promote the migration of polymorphonuclear cells (PMN). Moreover, soluble factors released from A. fumigatus-infected DC increased also the surface expression of two activation markers, CD11b and CD18, on PMN. A. fumigatus infection resulted also in CCL3, CCL4, CXCL10 and CCL20 productions that induce the migration of effector memory Th1 cells. Moreover, the late expression of CCL19 suggests that A. fumigatus-infected DC could be implicated in the migration of CCR7⁺ naïve T cells and mature DC in lymph nodes. Together these results suggested the involvement of human DC in the regulation of innate and adaptive immunity against A. fumigatus through the recruitment of cells active in the fungal destruction.     

Obesity Impairs Lymphatic Fluid Transport and Dendritic Cell Migration to Lymph Nodes

Introduction

Obesity is a major cause of morbidity and mortality resulting in pathologic changes in virtually every organ system. Although the cardiovascular system has been a focus of intense study, the effects of obesity on the lymphatic system remain essentially unknown. The purpose of this study was to identify the pathologic consequences of diet induced obesity (DIO) on the lymphatic system.

Methods

Adult male wild-type or RAG C57B6-6J mice were fed a high fat (60%) or normal chow diet for 8–10 weeks followed by analysis of lymphatic transport capacity. In addition, we assessed migration of dendritic cells (DCs) to local lymph nodes, lymph node architecture, and lymph node cellular make up.

Results

High fat diet resulted in obesity in both wild-type and RAG mice and significantly impaired lymphatic fluid transport and lymph node uptake; interestingly, obese wild-type but not obese RAG mice had significantly impaired migration of DCs to the peripheral lymph nodes. Obesity also resulted in significant changes in the macro and microscopic anatomy of lymph nodes as reflected by a marked decrease in size of inguinal lymph nodes (3.4-fold), decreased number of lymph node lymphatics (1.6-fold), loss of follicular pattern of B cells, and dysregulation of CCL21 expression gradients. Finally, obesity resulted in a significant decrease in the number of lymph node T cells and increased number of B cells and macrophages.

Conclusions

Obesity has significant negative effects on lymphatic transport, DC cell migration, and lymph node architecture. Loss of T and B cell inflammatory reactions does not protect from impaired lymphatic fluid transport but preserves DC migration capacity. Future studies are needed to determine how the interplay between diet, obesity, and the lymphatic system modulate systemic complications of obesity.     

Dendritic cells,chemokine receptors and autoimmune inflammatory diseases

Dendritic cells (DC) have been implicated in the induction of autoimmune diseases and have been identified in lesions associated with several autoimmune inflammatory diseases. Since DC are regarded as the professional antigen-presenting cell (APC) of the immune system and the only APC capable of activating na?ve T cells, they are likely to play a significant role in breaking tolerance of self-reactive lymphocytes and in supporting autoimmune responses in these diseases. A number of studies have revealed that small molecular weight chemotactic proteins known as chemokines are present within the autoimmune lesions and may contribute to the recruitment not only of DC populations, but also of immune cells such as T cells, B cells, neutrophils and monocytes into the site, and to the formation of organized lymphoid tissue structures within the target organ. The focus of this review will be a discussion of the role of chemokines in the recruitment of DC in human autoimmune inflammatory disorders, specifically the trafficking of DC into the inflammatory sites and the subsequent migration of differentiated DC from the inflammatory sites into the draining lymph nodes. Once DC are properly positioned within the lymph nodes, circulating antigen specific na?ve T cells can interact with DC and become activated, clonally expanded and stimulated to undergo differentiation into antigen-experienced memory T cells. Subsequent reactivation of memory T cells that enter the autoimmune lesions by DC present in the inflammatory lesion is thought to play a central role in tissue inflammation.     

CC chemokine ligand 18, an atopic dermatitis-associated and dendritic cell-derived chemokine, is regulated by staphylococcal products and allergen exposure

Atopic dermatitis is a chronic inflammatory skin disease with a steadily increasing prevalence. Exposure to allergens or bacterial superantigens triggers T and dendritic cell (DC) recruitment and induces atopic skin inflammation. In this study, we report that among all known chemokines CCL18/DC-CK1/PARC represents the most highly expressed ligand in atopic dermatitis. Moreover, CCL18 expression is associated with an atopic dermatitis phenotype when compared with other chronic inflammatory skin diseases. DCs either dispersed within the dermis or clustering at sites showing perivascular infiltrates are abundant sources of CCL18. In vitro, microbial products including LPS, peptidoglycan, and mannan, as well as the T cell-derived activation signal CD40L, induced CCL18 in monocytes. In contrast to monocytes, monocyte-derived, interstitial-type, and Langerhans-type DCs showed a constitutive and abundant expression of CCL18. In comparison to Langerhans cells, interstitial-type DCs produced higher constitutive levels of CCL18. In vivo, topical exposure to the relevant allergen or the superantigen staphylococcal enterotoxin B, resulted in a significant induction of CCL18 in atopic dermatitis patients. Furthermore, in nonatopic NiSO4-sensitized individuals, only relevant allergen but not irritant exposure resulted in the induction of CCL18. Taken together, findings of the present study demonstrate that CCL18 is associated with an atopy/allergy skin phenotype, and is expressed at the interface between the environment and the host by cells constantly screening foreign Ags. Its regulation by allergen exposure and microbial products suggests an important role for CCL18 in the initiation and amplification of atopic skin inflammation.     

Homeostatic lymphoid chemokines synergize with adhesion ligands to trigger T and B lymphocyte chemokinesis

Homeostatic chemokines such as CCL19, CCL21, and CXCL13 are known to elicit chemotaxis from naive T and B cells and play a critical role in lymphocyte homing to appropriate zones within secondary lymphoid organs (SLO). Here we tested whether CCL21 and CXCL13 modulate murine lymphocyte motility in the absence of concentration gradients, using videomicroscopy to directly observe the migration of single cells. CCL21 treatment of T cells induced rapid polarization and sustained random migration with average speeds of 5.16 +/- 2.08 microm/min; B cell migration (average velocity 4.10 +/- 1.58 microm/min) was similarly induced by CXCL13. Migration required the presence of both chemokine and adhesion ligands and was sustained for >24 h. Furthermore, in in vitro assays modeling the relative infrequency of Ag-specific T cell-dendritic cell (DC) encounters during primary immune responses, we found that CCL21 addition to T-DC cocultures accelerated the kinetics of CD69 up-regulation and enhanced by 2-fold the proliferation of Ag-specific T cells in a manner dependent on G-protein-coupled receptor signaling in T cells. These results suggest that homeostatic chemokines could substantially impact the dynamics and priming of lymphocytes within SLO even in the absence of significant concentration gradients.     

Binding of lymphoid chemokines to collagen IV that accumulates in the basal lamina of high endothelial venules: its implications in lymphocyte trafficking

Certain lymphoid chemokines are selectively and constitutively expressed in the high endothelial venules (HEV) of lymph nodes and Peyer's patches, where they play critical roles in the directional migration of extravasating lymphocytes into the lymphoid tissue parenchyma. How these chemokines are selectively localized and act in situ, however, remains unclear. In the present study, we examined the possibility that basal lamina-associated extracellular matrix proteins in the HEVs are responsible for retaining the lymphoid chemokines locally. Here we show that collagen IV (Col IV) bound certain lymphoid chemokines, including CCL21, CXCL13, and CXCL12, more potently than did fibronectin or laminin-1, but it bound CCL19 and CCL5 only weakly, if at all. Surface plasmon resonance analysis indicated that Col IV bound CCL21 with a low nanomolar K(D), which required the C-terminal region of CCL21. Col IV can apparently hold these chemokines in their active form upon binding, because the Col IV-bound chemokines induced lymphocyte migration efficiently in vitro. We found by immunohistochemistry that Col IV and CCL21, CXCL13, and CXCL12 were colocalized in the basal lamina of HEVs. When injected s.c. into plt/plt mice, CCL21 colocalized at least partially with Col IV on the basal lamina of HEVs in draining lymph nodes. Collectively, our results suggest that Col IV contributes to the creation of a lymphoid chemokine-rich environment in the basal lamina of HEVs by binding an array of locally produced lymphoid chemokines that promote directional lymphocyte trafficking from HEVs into the lymphoid tissue parenchyma.     

All-trans retinoic acid enhances murine dendritic cell migration to draining lymph nodes via the balance of matrix metalloproteinases and their inhibitors

Cancers escape immune surveillance through the manipulation of the host's immune system. Sequestration of dendritic cells (DCs) within tumor tissues and the subsequent inhibition of their migration is one of the several mechanisms by which tumors induce immunosuppression. In view of recent findings depicting the improvement of tumor immune responses in cancer patients following all-trans retinoic acid (ATRA) treatment, we sought to identify the effects of ATRA on DC mobility in the context of tumor immunotherapy. Our results demonstrate that ATRA, added to differentiating murine bone marrow progenitor cells, enhances the invasive capacity of the resulting DCs. Immature DCs injected intratumorally in mice show increased accumulation in draining lymph nodes, but not in nondraining lymph nodes and spleens, when differentiated in the presence of ATRA. The in vitro migration of mature DCs through the basement membrane matrix toward the lymphoid chemokines CCL19 and CCL21 is enhanced in these cells, albeit not in the presence of a matrix metalloproteinase (MMP) inhibitor. An increase in MMP production with a simultaneous decrease in the production of their inhibitors (tissue inhibitors of matrix metalloproteinase or TIMPs) is provoked by ATRA. This affects the MMP/TIMP balance in DCs, in particular that of MMP-9 and TIMP-1, favoring protease activity and thus allowing for enhanced DC mobilization. In conclusion, this study demonstrates that ATRA is capable of improving DC trafficking in a tumor milieu and, in view of the encouraging results obtained in the clinic, further supports the notion that ATRA might be a valuable chemical adjuvant to current immunotherapeutic strategies for cancer.     

Expression of the self-marker CD47 on dendritic cells governs their trafficking to secondary lymphoid organs

Dendritic cells (DCs) capture and process Ag in the periphery. Thus, traffic through lymphatic vessels is mandatory before DCs relocate to lymph nodes where they are dedicated to T-cell priming. Here, we show that the ubiquitous self-marker CD47 selectively regulates DC, but not T and B cell trafficking across lymphatic vessels and endothelial barriers in vivo. We find an altered skin DC migration and impaired T-cell priming in CD47-deficient mice at steady state and under inflammatory conditions. Competitive DC migration assays and active immunization with myeloid DCs demonstrate that CD47 expression is required on DCs but not on the endothelium for efficient DC trafficking and T-cell responses. This migratory defect correlates with the quasi-disappearance of splenic marginal zone DCs in nonmanipulated CD47-deficient mice. Nonetheless, CCR7 expression and CCL19-driven chemotaxis remain intact. Our data reveal that CD47 on DCs is a critical factor in controlling migration and efficient initiation of the immune response.     

Monocyte-derived dendritic cells exposed to Der p 1 allergen enhance the recruitment of Th2 cells: major involvement of the chemokines TARC/CCL17 and MDC/CCL22

Dendritic cells (DC) are potent antigen - presenting cells that can orientate the immune response towards a Th1 or a Th2 type. DC produce chemokines that are involved in the recruitment of either Th1 cells, such as IP10 (CXCL10), Th2 cells such as TARC (CCL17) and MDC (CCL22), or non-polarized T cells such as RANTES (CCL5) and MIP-lalpha (CCL3). We investigated whether monocyte-derived DC (MD-DC) generated from healthy donors or from patients sensitive to Dermatophagoides pteronyssinus (Dpt) and exposed to the cysteine-protease Der p 1(allergen of Dpt), could upregulate the expression of chemokines involved in type 1 or type 2 T cell recruitment. MD-DC were pulsed with either Der p 1 or with LPS as the control and the chemokines produced were evaluated using ELISA and chemotaxis assays. Der p 1-pulsed DC from allergic patients showed increased TARC (CCL17) and MDC (CCL22) production without modifying IP-10 (CXCL10) release. Der p 1-pulsed DC from healthy donors showed only increased IP-10 (CXCL10) secretion. RANTES (CCL5) and MIP-lalpha (CCL3) production were similarly increased when DC were from healthy or allergic donors. The selective Th2 clone recruitment activity of supernatants from Der p 1-pulsed DC of allergic patients was inhibited by anti-TARC (CCL17) and anti-MDC (CCL22) neutralizing Abs. By using anti-IP10 (CXCL10) blocking Abs, supernatants of Der p 1-pulsed DC from healthy donors were shown to be involved in the recruitment of Th1 cells. These results suggest that in allergic patients exposed to house dust mites, DC may favour the exacerbation of the Th2 response via the increase in type 2 chemokine production.     

Dendritic cells express CCR7 and migrate in response to CCL19 (MIP-3beta) after exposure to Helicobacter pylori

Helicobacter pylori infection induces chronic inflammation in the gastric mucosa with a marked increase in the number of lymphoid follicles consisting of infiltrating B and T cells, neutrophils, dendritic cells (DC) and macrophages. It has been suggested that an accumulation of mature DC in the tissue, resulting from a failure of DC to migrate to lymph nodes, may contribute to this chronic inflammation. Migration of DC to lymph nodes is regulated by chemokine receptor CCR7, expressed on mature DC, and the CCR7 ligands CCL19 and CCL21. In this study we analysed the maturation, in vitro migration and cytokine production of human DC after stimulation with live H. pylori. For comparison, DC responses to non-pathogenic Escherichia coli bacteria were also evaluated. Stimulation with H. pylori induced maturation of DC, i.e. up-regulation of the chemokine receptors CCR7 and CXCR4 and the maturation markers HLA-DR, CD80 and CD86. The H. pylori-stimulated DC also induced CD4(+) T-cell proliferation. DC stimulated with H. pylori secreted significantly more interleukin (IL)-12 compared to DC stimulated with E. coli, while E. coli-stimulated DC secreted more IL-10. Despite low surface expression of CCR7 protein following stimulation with H. pylori compared to E. coli, the DC migrated equally well towards CCL19 after stimulation with both bacteria. Thus, we could not detect any failure in the migration of H. pylori stimulated DC in vitro that may contribute to chronic gastritis in vivo, and our results suggest that H. pylori induces maturation and migration of DC to lymph nodes where they promote T cell responses.     

Differential binding of chemokines to macrophages and neutrophils in the human inflamed synovium

In chronic inflammatory foci, such as the rheumatoid joint, there is enhanced recruitment of phagocytes from the blood into the tissues. Chemokines are strongly implicated in directing the migration of these cells, although little is known regarding the chemokine receptors that could mediate their chemotaxis into the joint tissue. Therefore the objective of the study was to identify chemokine binding sites on macrophages and neutrophils within the rheumatoid synovium using radiolabeled ligand binding and in situ autoradiography. Specific binding sites for CCL3 (macrophage inflammatory protein-1α), CCL5 (RANTES), CCL2 (monocyte chemoattractant protein-1) and CXCL8 (IL-8) were demonstrated on CD68⁺ macrophages in the subintimal and intimal layers. The number and percentage of intimal cells that bound chemokines were greater in inflamed regions compared to noninflamed regions. The intensity of intimal binding varied between chemokines with the rank order, CCL3 > CCL5 > CCL2 > CXCL8. Neutrophils throughout the synovium bound CXCL8 but did not show any signal for binding CCL2, CCL3 or CCL5.     

T lymphocyte chemotactic chemokines in acute myelogenous leukemia (AML): local release by native human AML blasts and systemic levels of CXCL10 (IP-10), CCL5 (RANTES) and CCL17 (TARC)

T cell targeting immunotherapy is now considered in acute myelogenous leukemia (AML), and local recruitment of antileukemic T cells to the AML microcompartment will then be essential. This process is probably influenced by both intravascular as well as extravascular levels of T cell chemotactic chemokines. We observed that native human AML cells usually showed constitutive secretion of the chemotactic chemokines CXCL10 and CCL5, whereas CCL17 was only released for a subset of patients and at relatively low levels. Coculture of AML cells with nonleukemic stromal cells (i.e., fibroblasts, osteoblasts) increased CXCL10 and CCL17 levels whereas CCL5 levels were not altered. However, a wide variation between patients in both CXCL10 and CCL5 levels persisted even in the presence of the stromal cells. Neutralization of CXCL10 and CCL5 inhibited T cell migration in the presence of native human AML cells. Furthermore, serum CCL17 and CXCL10 levels varied between AML patients and were determined by disease status (both chemokines) as well as patient age, chemotherapy and complicating infections (only CCL17). Thus, extravascular as well as intravascular levels of T cell chemotactic chemokines show a considerable variation between patients that may be important for T cell recruitment and the effects of antileukemic T cell reactivity in local AML compartments.     

The chemokine receptors ACKR2 and CCR2 reciprocally regulate lymphatic vessel density

Macrophages regulate lymphatic vasculature development; however, the molecular mechanisms regulating their recruitment to developing, and adult, lymphatic vascular sites are not known. Here, we report that resting mice deficient for the inflammatory chemokine‐scavenging receptor, ACKR2, display increased lymphatic vessel density in a range of tissues under resting and regenerating conditions. This appears not to alter dendritic cell migration to draining lymph nodes but is associated with enhanced fluid drainage from peripheral tissues and thus with a hypotensive phenotype. Examination of embryonic skin revealed that this lymphatic vessel density phenotype is developmentally established. Further studies indicated that macrophages and the inflammatory CC‐chemokine CCL2, which is scavenged by ACKR2, are associated with this phenotype. Accordingly, mice deficient for the CCL2 signalling receptor, CCR2, displayed a reciprocal phenotype of reduced lymphatic vessel density. Further examination revealed that proximity of pro‐lymphangiogenic macrophages to developing lymphatic vessel surfaces is increased in ACKR2‐deficient mice and reduced in CCR2‐deficient mice. Therefore, these receptors regulate vessel density by reciprocally modulating pro‐lymphangiogenic macrophage recruitment, and proximity, to developing, resting and regenerating lymphatic vessels.     

CCR5-deficient mice control Mycobacterium tuberculosis infection despite increased pulmonary lymphocytic infiltration

The control of Mycobacterium tuberculosis infection is dependent on the development of an adaptive immune response, which is mediated by granulomas. The granuloma is a dynamic structure that forms in the lung and consists primarily of macrophages and lymphocytes. For this structure to be effective in containment of the bacillus, it must develop in an organized and timely manner. The formation of the granuloma is dependent on recruitment of activated cells through adhesion molecules and chemokines. M. tuberculosis infection causes an increase in the expression of beta-chemokines CCL3, CCL4, and CCL5, and their receptor CCR5, in the lungs. In this study, we demonstrate that CCR5-transgenic knockout mice were capable of recruiting immune cells to the lung to form granulomas. CCR5(-/-) mice successfully induced a Th1 response and controlled infection. Unexpectedly, M. tuberculosis infection in these mice resulted in greater numbers of lymphocytes migrating to the lung and higher levels of many inflammatory cytokines, compared with wild-type mice, without apparent long-term detrimental effects. In the absence of CCR5, there were more dendritic cells in the lung-draining lymph nodes and more primed T lymphocytes in these mice. Bacterial numbers in the lymph nodes were also higher in CCR5(-/-) mice. Therefore, CCR5 may play a role in the migration of dendritic cells to and from the lymph nodes during M. tuberculosis infection.     

Inhibition of generation of cytotoxic T lymphocyte activity by a CCL19/macrophage inflammatory protein (MIP)-3beta antagonist

Chemokines constitute a group of over 40 secreted peptides that are important for the control of leukocyte migration both during homeostasis and inflammation. Recent studies have implicated the ligands CCL19 and CCL21 and their receptor, CCR7, in the specific migration of na?ve lymphocytes and mature dendritic cells to secondary lymphoid organs during immune homeostasis. However, the role that these molecules play during immune priming is not well understood. In this study, using CCL19((8-83)), a novel N-terminal truncation mutant, we have investigated the role of CCL19 in a primary allogeneic immune response, a response of particular relevance to transplant rejection. This antagonist specifically inhibited wild type CCL19-induced chemotaxis and intracellular calcium mobilization without affecting that of CCL21. The treatment of mice with CCL19((8-83)) did not globally inhibit the recruitment of cells into lymph nodes; however, it inhibited the generation of cytotoxic T lymphocytes toward allogeneic dendritic cells. This is the first evidence that CCL19 plays a role in immune priming.     

Neutrophil-Derived CCL3 Is Essential for the Rapid Recruitment of Dendritic Cells to the Site of Leishmania major Inoculation in Resistant Mice

Neutrophils are rapidly and massively recruited to sites of microbial infection, where they can influence the recruitment of dendritic cells. Here, we have analyzed the role of neutrophil released chemokines in the early recruitment of dendritic cells (DCs) in an experimental model of Leishmania major infection. We show in vitro, as well as during infection, that the parasite induced the expression of CCL3 selectively in neutrophils from L. major resistant mice. Neutrophil-secreted CCL3 was critical in chemotaxis of immature DCs, an effect lost upon CCL3 neutralisation. Depletion of neutrophils prior to infection, as well as pharmacological or genetic inhibition of CCL3, resulted in a significant decrease in DC recruitment at the site of parasite inoculation. Decreased DC recruitment in CCL3^−/− mice was corrected by the transfer of wild type neutrophils at the time of infection. The early release of CCL3 by neutrophils was further shown to have a transient impact on the development of a protective immune response. Altogether, we identified a novel role for neutrophil-secreted CCL3 in the first wave of DC recruitment to the site of infection with L. major, suggesting that the selective release of neutrophil-secreted chemokines may regulate the development of immune response to pathogens.     

Defective dendritic cell migration and activation of adaptive immunity in PI3Kgamma-deficient mice

Gene-targeted mice were used to evaluate the role of the gamma isoform of phosphoinositide 3-kinase (PI3Kgamma) in dendritic cell (DC) migration and induction of specific T-cell-mediated immune responses. DC obtained from PI3Kgamma-/- mice showed a reduced ability to respond to chemokines in vitro and ex vivo and to travel to draining lymph nodes under inflammatory conditions. PI3Kgamma-/- mice had a selective defect in the number of skin Langerhans cells and in lymph node CD8alpha- DC. Furthermore, PI3Kgamma-/- mice showed a defective capacity to mount contact hypersensitivity and delayed-type hypersensitivity reactions. This defect was directly related to the reduced ability of antigen-loaded DC to migrate from the periphery to draining lymph nodes. Thus, PI3Kgamma plays a nonredundant role in DC trafficking and in the activation of specific immunity. Therefore, PI3Kgamma may be considered a new target to control exaggerated immune reactions.