Enhanced ovalbumin-induced airway inflammation in CD26-/- mice

High-fat diet and palmitic acid amplify airway type 2 inflammation

Introduction

Metabolic dysfunction such as elevated levels of saturated fatty acids (SFA) may play a role in obese asthma, but its contribution to airway inflammation remains unclear. We sought to determine the role of high-fat diet (HFD) and palmitic acid (PA), a major form of SFA, in regulating type 2 inflammation.

Methods

Airway samples from asthma patients with or without obesity, mouse models and human airway epithelial cell culture were utilized to test if SFA amplify type 2 inflammation.

Results

Asthma patients with obesity had higher levels of airway PA than asthma patients without obesity. HFD increased the levels of PA in mice, and subsequently enhanced IL-13-induced airway eosinophilic inflammation. PA treatment amplified airway eosinophilic inflammation in mice that were previously exposed to IL-13 or house dust mite. IL-13 alone or in combination with PA increased dipeptidyl peptidase 4 (DPP4) release (soluble DPP4) and/or activity in mouse airways and human airway epithelial cells. Inhibition of DPP4 activity by linagliptin in mice pre-exposed to IL-13 or both IL-13 and PA increased airway eosinophilic and neutrophilic inflammation.

Discussion

Our results demonstrated the exaggerating effect of obesity or PA on airway type 2 inflammation. Up-regulation of soluble DPP4 by IL-13 and/or PA may serve as a mechanism to prevent excessive type 2 inflammation. Soluble DPP4 may have the therapeutic potential in asthma patients with obesity who have an endotype with mixed airway eosinophilic and neutrophilic inflammation.

Association between novel Glucose-Lowering drugs and risk of Asthma: A network Meta-Analysis of cardiorenal outcome trials

AIMS

This network meta-analysis aimed to evaluate the asthma risk associated with dipeptidyl peptidase (DPP)-4 inhibitors, glucagon-like peptide-1 receptor agonists (GLP-1RAs), and sodium-glucose co-transporter (SGLT) 2 inhibitors.

METHODS

Electronic databases were systematically searched up to March 2021 to include placebo-controlled cardiovascular (or cardiorenal) outcome trials that reported the asthma incidents in patients taking DPP-4 inhibitors, GLP-1RAs, or SGLT2 inhibitors. A random-effects network meta-analysis was conducted to estimate their odds ratio (ORs) and 95% confidence intervals (CIs).

RESULTS

Nineteen trials including 218 asthma cases among 159,705 patients were included. Compared with placebo, SGLT2 inhibitors (OR, 0.59; 95% CI, 0.38-0.93) were significantly associated with a decreased risk of asthma while both DPP-4 inhibitors and GLP-1RAs did not significantly affect asthma risk. SGLT2 inhibitors were significantly associated with a lower risk of asthma than DPP-4 inhibitors (OR, 0.38; 95% CI, 0.18-0.79). There was no association between GLP-1RAs and DPP-4 inhibitors and between SGLT2 inhibitors and GLP-1RAs in risk of asthma.

CONCLUSIONS

SGLT2 inhibitors might protect against asthma while DPP-4 inhibitors and GLP-1RAs did not significantly affect the asthma incident. Given the underreporting of asthma in this study, further investigations using real-world data as well as mechanistic studies are warranted to confirm our results.

Involvement of CD26 in Differentiation and Functions of Th1 and Th17 Subpopulations of T Lymphocytes

CD26, acting as a costimulator of T cell activation, plays an important role in the immune system. However, the role of CD26 in the differentiation of T cell subsets, especially of new paradigms of T cells, such as Th17 and Tregs, is not fully clarified. In the present study, the role of CD26 in T cell differentiation was investigated in vitro. CD26 expression was analyzed in the different subsets of human peripheral blood T lymphocytes after solid-phase immobilized specific anti-CD3 mAb stimulation. Here, the percentage of CD4⁺ cells significantly increased and most of these cells were coexpressed with CD26, suggesting a close correlation of CD26 expression with the proliferation of CD4⁺ cells. Subsequently, after immobilized anti-CD3 mAb stimulation, CD26 high-expressing cells (CD26^high) were separated from CD26 low-expressing cells (CD26^low) by magnetic cell sorting. We found that the percentages of cells secreting Th1 typical cytokines (IL-2, IFN-γ) and Th17 typical cytokines (IL-6, IL-17, and IL-22) or expressing Th17 typical biomarkers (IL-23R, CD161, and CD196) in the CD26^high group were markedly higher than in those in the CD26^low group. In addition, a coexpression of CD26 with IL-2, IFN-γ, IL-17, IL-22, and IL-23R in lymphocytes was demonstrated by fluorescence microscopy. These results provide direct evidence that the high expression of CD26 is accompanied by the differentiation of T lymphocytes into Th1 and Th17, indicating that CD26 plays a crucial role in regulating the immune response.

Drug-Induced Cough

Since the recognition of angiotensin-converting enzyme inhibitors (ACEIs)-induced cough, drug has been considered as a potential cause of chronic cough. This review presents recent knowledge on drug-induced coughs in patients with chronic cough. The focus is placed on ACEIs, for which there are a multitude of studies documenting their associations with cough. Additional drugs are discussed for which there are reports of cough as a side effect of treatment, and the potential mechanisms of these effects are discussed.

Emerging Roles of Dipeptidyl Peptidase-4 Inhibitors in Delaying the Progression of Type 1 Diabetes Mellitus

Type 1 diabetes mellitus (T1DM) results from the immune cell-mediated destruction of functional pancreatic β-cells. In the presymptomatic period, T1DM is characterized by the presence of two or more autoantibodies against the islet cells in patients without glycemic decompensation. Therapeutic strategies that can modify the autoimmune process could slow the progression of T1DM. Dipeptidyl peptidase-4 (DPP-4) or CD26, a multifunctional serine protease with a dual function (regulatory protease and binding protein), can modulate inflammation and immune cell-mediated β-cell destruction. CD26 is involved in T-cell co-stimulation, migration, memory development, thymic maturation, and emigration patterns. DPP-4 degrades the peptide hormones GLP-1 and GIP. In addition to regulating glucose metabolism, DPP-4 exerts anti-apoptotic, regenerative, and proliferative effects to promote β-cell mass expansion. GLP-1 receptor signaling may regulate murine lymphocyte proliferation and maintenance of peripheral regulatory T-cells. In patients with T1DM, the serum DPP-4 activity is upregulated. Several studies have suggested that the upregulated DPP-4 activity is correlated with T1DM pathophysiology. DPP-4, which is preferentially expressed on the Th1 surface, can promote the polarization of Th1 immunity, a prerequisite for T1DM development. CD26 inhibition can suppress T-cell proliferation and Th1 cytokine production and stimulate tumor growth factor beta-1 (TGF-β1) secretion, which plays an important role in the regulation of autoimmunity in T1DM. Studies on humans or animal models of T1DM have suggested that DPP-4 inhibitors can improve β-cell function and attenuate autoimmunity in addition to decreasing insulin dependence. This review summarizes the emerging roles of DPP-4 inhibitors in potentially delaying the progression of T1DM.

Vildagliptin, a CD26/DPP4 inhibitor, ameliorates bleomycin-induced pulmonary fibrosis via regulating the extracellular matrix

BACKGROUND

Idiopathic pulmonary fibrosis is a debilitating lung disease. CD26/DPP4 plays promotive roles in pulmonary damage and fibrosis. This study aimed to explore the roles of vildagliptin in bleomycin-induced pulmonary fibrosis, and to address its ameliorative effect on the extracellular matrix (ECM).

METHODS

Idiopathic pulmonary fibrosis mice models were induced by intratracheal injection of bleomycin. DPP4 activity was evaluated, and the fibrosis was investigated by Hematoxylin-eosin, Masson's trichrome staining and hydroxyproline assay. Expression of extracellular matrix proteins including α-SMA, collagen IV, collagen I, FN and TGF-β were analyzed by immunochemistry and western blot. Percentages of the numbers of monocytes, leukocytes, basophils and lymphocytes were classified, and inflammatory factors in plasma as well as lung tissues were examined by enzyme-linked immunosorbent assay and western blot. The influences of vildagliptin on TGF-β1-induced cell proliferation, differentiation and inflammatory factors in MRC-5 cells were detected.

RESULTS

Vildagliptin effectively attenuated inflammation and fibrosis in bleomycin-induced pulmonary tissue via inhibiting the activity of CD26/DPP4. extracellular matrix proteins were suppressed by vildagliptin. Thus, lung tissue fibrosis was efficiently alleviated by vildagliptin.

CONCLUSION

As an inhibitor of CD26/DPP4, Vildagliptin could be a promising therapeutic candidate for idiopathic pulmonary fibrosis.

Dipeptidyl peptidase 4 inhibitors and their potential immune modulatory functions

Dipeptidyl peptidase 4 (DPP4) inhibitors (DPP4is) are oral anti-diabetic drugs (OADs) for the treatment of type 2 diabetes mellitus (T2DM) through inhibiting the degradation of incretin peptides. Numerous investigations have been focused on the effects of DPP4is on glucose homeostasis. However, there are limited evidences demonstrating their Potential modulatory functions in the immune system. DPP4, originally known as the lymphocyte cell surface protein CD26, is widely expressed in many types of immune cells including CD4(+) and CD8(+) T cells, B cells, NK cells, dendritic cells, and macrophages; and regulate the functions of these cells. In addition, DPP4 is capable of modulating plenty of cytokines, chemokines and peptide hormones. Accordingly, DPP4/CD26 is speculated to be involved in various immune/inflammatory diseases and DPP4is may become a new drug class applied in these diseases. This review focuses on the regulatory effects of DPP4is on immune functions and their possible underlying mechanisms. Further clinical studies will be necessitated to fully evaluate the administration of DPP4is in diabetic patients with or without immune diseases.

The roles of dipeptidyl peptidase-4 and its inhibitors in the regulation of airway epithelial-mesenchymal transition

Objective: Dipeptidyl peptidase 4 (DPP4), also known as CD26, is a transmembrane glycoprotein with peptidase activity expressed on epithelial cells and some immune cells. It also occurs as a soluble form. Studies have revealed that the expression level of lymphocyte sCD26/sDPP4 was elevated in the asthmatic patients. Airway remodeling increases in asthma severity and these structural changes include, amongst others, the loss of epithelial integrity because of cell shedding, goblet cell hyperplasia, destruction of ciliated cells, and EMT. So we try to find whether sCD26/sDPP4 has a role in pathological/dysregulated transition from bronchial epithelial cells into fibroblasts cells in response to TGFβ1 exposure in vitro. Therefore, our purpose in the present work was to identify the role of sCD26/sDPP4 in airway EMT regulation. Methods: The EMT cell model was established based on human 16HBE cells. The effects of sCD26/sDPP4 and its inhibitors on airway EMT and that of sCD26/sDPP4 on Th17/IL-17 and its role in airway EMT were investigated in vitro. Results: The mRNA and protein level of E-Cadherin decreased after the treatment of TGF-β1 in 16HBE cells, while α-SMA was up-regulated. The level of E-Cadherin was significantly down-regulated after the sCD26/sDPP4 stimulation, and that of α-SMA was dramatically elevated. DPP4 inhibitors promoted the level of E-cadherin and inhibited that of α-SMA. Additionally, in the DPP4-treated IL-17 cells group, E-Cadherin was markedly down-regulated at the mRNA and protein level, while α-SMA was reversely up-regulated. Conclusion: The TGF-β1-induced EMT of human bronchial epithelial cells could be promoted by sCD26/sDPP4. The suppression of EMT in human bronchial epithelial cells was achieved by DPP4 inhibitor, and the TGF-β1-mediated EMT of human airway cells was promoted by the synergy of IL-17 and sCD26/sDPP4 in vitro.

CD26 and Asthma: a Comprehensive Review

Asthma is a heterogeneous and chronic inflammatory family of disorders of the airways with increasing prevalence that results in recurrent and reversible bronchial obstruction and expiratory airflow limitation. These diseases arise from the interaction between environmental and genetic factors, which collaborate to cause increased susceptibility and severity. Many asthma susceptibility genes are linked to the immune system or encode enzymes like metalloproteases (e.g., ADAM-33) or serine proteases. The S9 family of serine proteases (prolyl oligopeptidases) is capable to process peptide bonds adjacent to proline, a kind of cleavage-resistant peptide bonds present in many growth factors, chemokines or cytokines that are important for asthma. Curiously, two serine proteases within the S9 family encoded by genes located on chromosome 2 appear to have a role in asthma: CD26/dipeptidyl peptidase 4 (DPP4) and DPP10. The aim of this review is to summarize the current knowledge about CD26 and to provide a structured overview of the numerous functions and implications that this versatile enzyme could have in this disease, especially after the detection of some secondary effects (e.g., viral nasopharyngitis) in type II diabetes mellitus patients (a subset with a certain risk of developing obesity-related asthma) upon CD26 inhibitory therapy.

Expansion of different subpopulations of CD26-/low T cells in allergic and non-allergic asthmatics

CD26 displays variable levels between effector (TH₁₇ ≫ TH₁ > TH₂ > Treg) and naïve/memory (memory > naïve) CD4⁺ T lymphocytes. Besides, IL-6/IL⁻6R is associated with TH₁₇-differentiation and asthma severity. Allergic/atopic asthma (AA) is dominated by TH₂ responses, while TH₁₇ immunity might either modulate the TH₂-dependent inflammation in AA or be an important mechanism boosting non-allergic asthma (NAA). Therefore, in this work we have compared the expression of CD26 and CD126 (IL-6Rα) in lymphocytes from different groups of donors: allergic (AA) and non-allergic (NAA) asthma, rhinitis, and healthy subjects. For this purpose, flow cytometry, haematological/biochemical, and in vitro proliferation assays were performed. Our results show a strong CD26-CD126 correlation and an over-representation of CD26⁻ subsets with a highly-differentiated effector phenotype in AA (CD4⁺CD26^−/low T cells) and NAA (CD4⁻CD26⁻ γδ-T cells). In addition, we found that circulating levels of CD26 (sCD26) were reduced in both AA and NAA, while loss of CD126 expression on different leukocytes correlated with higher disease severity. Finally, selective inhibition of CD26-mRNA translation led to enhanced T cell proliferation in vitro. These findings support that CD26 down-modulation could play a role in facilitating the expansion of highly-differentiated effector T cell subsets in asthma.

Dipeptidyl peptidase-4(DPP-4) inhibitors: promising new agents for autoimmune diabetes

Dipeptidyl peptidase-4 (DPP-4) inhibitors constitute a novel class of anti-diabetic agents confirmed to improve glycemic control and preserve β-cell function in type 2 diabetes. Three major large-scale studies, EXAMINE, SAVOR-TIMI 53, and TECOS, have confirmed the cardiovascular safety profile of DPP-4 inhibitors. Based on these results, DPP-4 inhibitors have gained widespread use in type 2 diabetes treatment. It is currently unknown, however, whether DPP-4 inhibitors have similar therapeutic efficacy against autoimmune diabetes. Several in vitro and in vivo studies have addressed this issue, but the results remain controversial. In this review, we summarize experimental findings and preliminary clinical trial results, and identify potentially effective immune modulation targets of DPP-4 inhibitors for autoimmune diabetes.

Delayed allogeneic skin graft rejection in CD26-deficient mice

Organ transplantation is an effective therapeutic tool for treating many terminal diseases. However, one of the biggest challenges of transplantation is determining how to achieve the long-term survival of the allogeneic or xenogeneic transplant by, for example, preventing transplant rejection. In the current study, CD26 gene-knockout mice were used to investigate the potential role of CD26/dipeptidyl peptidase-4 (DPPIV) in allogeneic skin graft rejection by tail-skin transplantation. Compared with wild-type (CD26^+/+) counterparts, CD26^-/- mice showed reduced necrosis of grafts and delayed graft rejection after skin transplantation. Concentrations of serum IgG, including its subclasses IgG1 and IgG2a, were significantly reduced in CD26^-/- mice during graft rejection. Moreover, after allogeneic skin transplantation, the secretion levels of the cytokines IFN-γ, IL-2, IL-6, IL-4, and IL-13 were significantly reduced, whereas the level of the cytokine IL-10 was increased in the serum of CD26^-/- mice compared with that in the serum of CD26^+/+ mice. Additionally, the concentration of IL-17 in serum and the percentage of cells secreting IL-17 in mouse peripheral blood lymphocytes (MPBLs) were both significantly lower, while the percentage of regulatory T cells (Tregs) was significantly higher in MPBLs of CD26^-/- mice than in those of CD26^+/+ mice. Furthermore, a lower percentage of CD8⁺ T cells in MPBLs and fewer infiltrated macrophages and T cells in graft tissues of CD26^-/- mice were detected during graft rejection. These results indicate that CD26 is involved in allogeneic skin graft rejection and provides another hint that CD26 deficiency leads to less rejection due to lower activation and proliferation of host immune cells.

The effect of DPP-4 inhibitors on asthma control: an administrative database study to evaluate a potential pathophysiological relationship

Rationale

DPP-4 may regulate immunological pathways implicated in asthma. Assessing whether DPP-4 inhibitor (DPP-4i) use might affect asthma control is clinically important because DPP-4i use in type 2 diabetes mellitus management (T2DM) is increasing. This study evaluated associations between DPP-4i use and asthma control.

Methods

This was a retrospective, observational, matched cohort study using administrative claims in the MarketScan^® Commercial Claims and Encounters (Commercial) and Medicare Supplemental and Coordination of Benefits (Medicare Supplemental) databases. Adult asthma patients initiating an oral DPP-4i or a non-DPP-4i between November 1, 2006 and March 31, 2014 were included. Patients were followed for asthma-related outcomes for 12 months after initiation of the antidiabetes medication. Outcomes included risk-domain asthma control (RDAC), defined as no asthma hospitalizations, no lower respiratory tract infections, and no oral corticosteroid (OCS) prescriptions; overall asthma control (RDAC criteria plus limited short-acting beta agonist use); treatment stability (RDAC criteria plus no increase of ≥50% in inhaled corticosteroid dose or addition of other asthma therapy); and severe asthma exacerbation rates (asthma-related hospitalizations, emergency room visits, or acute treatments with OCS). Comparisons were made between two matched cohorts (DPP-4i vs. non-DPP-4i initiators) using multivariable logistic regression and generalized linear modeling. Covariates included baseline demographic and clinical characteristics related to asthma and T2DM.

Results

The adjusted odds of achieving RDAC (odds ratio [OR]: 1.05; 95% CI: 0.964 to 1.147), overall asthma control (OR: 1.04; 95% CI: 0.956 to 1.135), and treatment stability (OR: 1.04; 95% CI: 0.949 to 1.115) did not differ between the DPP-4i and non-DPP-4i cohorts. A difference was not found between cohorts in severe asthma exacerbation rates during the 12 months following initiation of antidiabetes treatment (mean = 0.32 vs. 0.34 exacerbations per subject-year, respectively; p=0.064).

Conclusion

Asthma control was similar between patients initiating DPP-4i and non-DPP-4i antidiabetes medications, suggesting no association between DPP-4i use and asthma control.

Fibroblast activation protein is dispensable in the anti-influenza immune response in mice

Fibroblast activation protein alpha (FAP) is a unique dual peptidase of the S9B serine protease family, being capable of both dipeptidyl peptidase and endopeptidase activities. FAP is expressed at low level in healthy adult organs including the pancreas, cervix, uterus, submaxillary gland and the skin, and highly upregulated in embryogenesis, chronic inflammation and tissue remodelling. It is also expressed by cancer-associated stromal fibroblasts in more than 90% of epithelial tumours. FAP has enzymatic and non-enzymatic functions in the growth, immunosuppression, invasion and cell signalling of tumour cells. FAP deficient mice are fertile and viable with no gross abnormality, but little data exist on the role of FAP in the immune system. FAP is upregulated in association with microbial stimulation and chronic inflammation, but its function in infection remains unknown. We showed that major populations of immune cells including CD4+ and CD8+ T cells, B cells, dendritic cells and neutrophils are generated and maintained normally in FAP knockout mice. Upon intranasal challenge with influenza virus, FAP mRNA was increased in the lungs and lung-draining lymph nodes. Nonetheless, FAP deficient mice showed similar pathologic kinetics to wildtype controls, and were capable of supporting normal anti-influenza T and B cell responses. There was no evidence of compensatory upregulation of other DPP4 family members in influenza-infected FAP-deficient mice. FAP appears to be dispensable in anti-influenza adaptive immunity.

Expression and Clinical Significance of Serum Dipeptidyl Peptidase IV Chronic Obstructive Pulmonary Disease

OBJECTIVE

The purpose of this study is to explore the correlation between serum dipeptidyl peptidase IV (DPPIV) and chronic obstructive pulmonary disease (COPD) at its various disease states, analyze its applications in the prediction and diagnosis of COPD and test the possibility of DPPIV as the serologic marker for COPD screening.

MATERIALS AND METHODS

Samples from 74 patients (42 cases with acute exacerbation of COPD or acute exacerbation COPD (AECOPD) and 32 cases with stable COPD) and 29 control subjects were collected in this study. Those patients with AECOPD were classified as COPD remission group if their clinical symptoms relieved after nonintravenous or oral hormone therapy for 7 ± 3 days. DPPIV concentration was measured by enzyme-linked immunosorbent assay, and the difference in serum concentration of DPPIV was compared among different groups. The correlation between DPPIV concentration and age, sex or smoking history was analyzed, and the diagnostic value of DPPIV was evaluated by receiver-operating characteristic (ROC) curve analysis.

RESULTS

Serum DPPIV concentration was significantly lower in all COPD groups as compared with that in healthy control group (P < 0.001). Serum DPPIV concentration in AECOPD group was increased after treatment (P < 0.001). There was no significant correlation between DPPIV concentration and age, sex or smoking history (P > 0.05). ROC analysis indicated that serum DPPIV concentration in all groups showed a good diagnostic accuracy, especially in stable COPD and AECOPD groups. The area under the ROC curve values were 0.901 and 0.906, respectively, with a high specificity of 0.931 for both groups and a high sensitivity of 0.75 for stable COPD and 0.875 for AECOPD.

CONCLUSIONS

Serum DPPIV concentration in patients with COPD is decreased significantly, and there is no correlation between serum DPPIV concentration and sex or age. Serum DPPIV not only is an independent predictive factor, but also of high value as a good serologic marker for the diagnosis of COPD.

Cut to the chase: a review of CD26/dipeptidyl peptidase-4's (DPP4) entanglement in the immune system

CD26/DPP4 (dipeptidyl peptidase 4/DP4/DPPIV) is a surface T cell activation antigen and has been shown to have DPP4 enzymatic activity, cleaving-off amino-terminal dipeptides with either L-proline or L-alanine at the penultimate position. It plays a major role in glucose metabolism by N-terminal truncation and inactivation of the incretins glucagon-like peptide-1 (GLP) and gastric inhibitory protein (GIP). In 2006, DPP4 inhibitors have been introduced to clinics and have been demonstrated to efficiently enhance the endogenous insulin secretion via prolongation of the half-life of GLP-1 and GIP in patients. However, a large number of studies demonstrate clearly that CD26/DPP4 also plays an integral role in the immune system, particularly in T cell activation. Therefore, inhibition of DPP4 might represent a double-edged sword. Apart from the metabolic benefit, the associated immunological effects of long term DPP4 inhibition on regulatory processes such as T cell homeostasis, maturation and activation are not understood fully at this stage. The current data point to an important role for CD26/DPP4 in maintaining lymphocyte composition and function, T cell activation and co-stimulation, memory T cell generation and thymic emigration patterns during immune-senescence. In rodents, critical immune changes occur at baseline levels as well as after in-vitro and in-vivo challenge. In patients receiving DPP4 inhibitors, evidence of immunological side effects also became apparent. The scope of this review is to recapitulate the role of CD26/DPP4 in the immune system regarding its pharmacological inhibition and T cell-dependent immune regulation.

Significant elevation of serum dipeptidyl peptidase-4 activity in young-adult type 1 diabetes

AIMS

Currently, inhibition of dipeptidyl peptidase-4 (DPP-4) is widely used in the treatment of type 2 diabetes. Application of this strategy is awaited as a new therapeutic approach for type 1 diabetes, but the scientific basis is still lacking. This report describes the evaluation of serum DPP-4 activity in type 1 diabetes compared with control subjects, and assessment of relationships between DPP-4 activity and diabetic complication markers and metabolic variables in type 1 diabetes.

METHODS

We examined serum DPP-4 activity in Japanese young-adult type 1 diabetes (n=76, females 69.7%, age 30.9 ± 6.2 years, duration of diabetes 16.5 ± 11.1 years; mean ± SD) and healthy controls (n=22). Association of the enzymatic activity with diabetic micro- and macro- vascular complication markers and clinical parameters was also assessed.

RESULTS

Subjects with type 1 diabetes displayed significantly higher serum DPP-4 activity than healthy controls (relative value, control: 1.00 ± 0.28, T1D, 1.29 ± 0.38; p=0.0011) independent of other clinical parameters. In type 1 diabetes, DPP-4 activity was positively correlated with duration of diabetes (r=0.248, p=0.031), while not correlated with HbA1c level. In univariate correlation analysis of diabetic complication markers and other metabolic parameters, coefficient of variation of R-R intervals (CVR-R) and gamma (γ)-glutamyltransferase (GGT) levels were correlated with DPP-4 activity. GGT was extracted as an independent variable of DPP-4 activity in multivariate analysis (β=0.213, p=0.035).

CONCLUSIONS

Serum DPP-4 activity is significantly elevated in Japanese type 1 diabetes, suggesting pathophysiological significance of the enzyme in type 1 diabetes.

Complement receptor C5aR1/CD88 and dipeptidyl peptidase-4/CD26 define distinct hematopoietic lineages of dendritic cells

Differential display of the integrins CD103 and CD11b are widely used to distinguish two major dendritic cell (DC) subsets in nonlymphoid tissues. CD103(+) DCs arise from FLT3-dependent DC precursors (preDCs), whereas CD11b(hi) DCs can arise either from preDCs or FLT3-independent monocytes. Functional characterization of these two lineages of CD11b(hi) DCs has been hindered by the lack of a widely applicable method to distinguish between them. We performed gene expression analysis of fractionated lung DCs from C57BL/6 mice and found that monocyte-derived DCs (moDCs), including CD11b(hi)Ly-6C(lo) tissue-resident and CD11b(hi)Ly-6C(hi) inflammatory moDCs, express the complement 5a receptor 1/CD88, whereas preDC-derived conventional DCs (cDCs), including CD103(+) and CD11b(hi) cDCs, express dipeptidyl peptidase-4/CD26. Flow cytometric analysis of multiple organs, including the kidney, liver, lung, lymph nodes, small intestine, and spleen, confirmed that reciprocal display of CD88 and CD26 can reliably distinguish FLT3-independent moDCs from FLT3-dependent cDCs in C57BL/6 mice. Similar results were obtained when DCs from BALB/c mice were analyzed. Using this novel approach to study DCs in mediastinal lymph nodes, we observed that most blood-derived lymph node-resident DCs, as well as tissue-derived migratory DCs, are cDCs. Furthermore, cDCs, but not moDCs, stimulated naive T cell proliferation. We anticipate that the use of Abs against CD88 and CD26 to distinguish moDCs and cDCs in multiple organs and mouse strains will facilitate studies aimed at assigning specific functions to distinct DC lineages in immune responses.

The chemokine system in innate immunity

Chemokines are chemotactic cytokines that control the migration and positioning of immune cells in tissues and are critical for the function of the innate immune system. Chemokines control the release of innate immune cells from the bone marrow during homeostasis as well as in response to infection and inflammation. They also recruit innate immune effectors out of the circulation and into the tissue where, in collaboration with other chemoattractants, they guide these cells to the very sites of tissue injury. Chemokine function is also critical for the positioning of innate immune sentinels in peripheral tissue and then, following innate immune activation, guiding these activated cells to the draining lymph node to initiate and imprint an adaptive immune response. In this review, we will highlight recent advances in understanding how chemokine function regulates the movement and positioning of innate immune cells at homeostasis and in response to acute inflammation, and then we will review how chemokine-mediated innate immune cell trafficking plays an essential role in linking the innate and adaptive immune responses.

Pharmacology, physiology, and mechanisms of action of dipeptidyl peptidase-4 inhibitors

Dipeptidyl peptidase-4 (DPP4) is a widely expressed enzyme transducing actions through an anchored transmembrane molecule and a soluble circulating protein. Both membrane-associated and soluble DPP4 exert catalytic activity, cleaving proteins containing a position 2 alanine or proline. DPP4-mediated enzymatic cleavage alternatively inactivates peptides or generates new bioactive moieties that may exert competing or novel activities. The widespread use of selective DPP4 inhibitors for the treatment of type 2 diabetes has heightened interest in the molecular mechanisms through which DPP4 inhibitors exert their pleiotropic actions. Here we review the biology of DPP4 with a focus on: 1) identification of pharmacological vs physiological DPP4 substrates; and 2) elucidation of mechanisms of actions of DPP4 in studies employing genetic elimination or chemical reduction of DPP4 activity. We review data identifying the roles of key DPP4 substrates in transducing the glucoregulatory, anti-inflammatory, and cardiometabolic actions of DPP4 inhibitors in both preclinical and clinical studies. Finally, we highlight experimental pitfalls and technical challenges encountered in studies designed to understand the mechanisms of action and downstream targets activated by inhibition of DPP4.

The new insights from DPP-4 inhibitors: their potential immune modulatory function in autoimmune diabetes

Dipeptidyl peptidase-4 (DPP-4) inhibitors are a new class of anti-diabetic agents that are widely used in clinical practice to improve glycemic control and protect β-cell function in patients with type 2 diabetes. DPP-4 is also known as lymphocyte cell surface protein CD26 and plays an important role in T-cell immunity. Autoimmune diabetes, a T-cell mediated organ-specific disease, is initiated by the imbalance between pathogenic and regulatory T-lymphocytes. DPP-4 inhibitors can suppress pathogenic effects of Th1 and Th17 cells and up-regulate Th2 cells and regulatory T cells, which play a critical role in ameliorating autoimmune diabetes. This provides a basis for the potential use of DPP-4 inhibitors in the treatment of autoimmune diabetes. Recent studies suggest that DPP-4 inhibitors improve β-cell function and attenuate autoimmunity in type 1 diabetic mouse models. However, there are few clinical studies on the treatment of autoimmune diabetes with DPP-4 inhibitors. Further studies are warranted to confirm the therapeutic effects of DPP-4 inhibitors on autoimmune diabetes in humans.

Ectoenzymes in leukocyte migration and their therapeutic potential

Inflammation causes or accompanies a huge variety of diseases. Migration of leukocytes from the blood into the tissues, in the tissues, and from the tissues to lymphatic vasculature is crucial in the formation and resolution of inflammatory infiltrates. In addition to classical adhesion and activation molecules, several other molecules are known to contribute to the leukocyte traffic. Several of them belong to ectoenzymes, which are cell surface molecules having catalytically active sites outside the cell. We will review here how several ectoenzymes present on leukocytes or endothelial cell surface function as adhesins and/or modulate the extravasation cascade through their enzymatic activities. Moreover, their therapeutic potential as immune modulators in different experimental inflammation models and in clinical trials will be discussed.

Chemokines and chemokine receptors: positioning cells for host defense and immunity

Chemokines are chemotactic cytokines that control the migratory patterns and positioning of all immune cells. Although chemokines were initially appreciated as important mediators of acute inflammation, we now know that this complex system of approximately 50 endogenous chemokine ligands and 20 G protein-coupled seven-transmembrane signaling receptors is also critical for the generation of primary and secondary adaptive cellular and humoral immune responses. Recent studies demonstrate important roles for the chemokine system in the priming of naive T cells, in cell fate decisions such as effector and memory cell differentiation, and in regulatory T cell function. In this review, we focus on recent advances in understanding how the chemokine system orchestrates immune cell migration and positioning at the organismic level in homeostasis, in acute inflammation, and during the generation and regulation of adoptive primary and secondary immune responses in the lymphoid system and peripheral nonlymphoid tissue.