The latter was achieved

The latter was achieved MAPK Inhibitor Library in vivo by generation of mixed BM chimeras through reconstitution of lethally irradiated WT recipient mice

with an equal mixture of B7-deficient (CD80−/−CD86−/−) BM 18 and CD11c:DTA (CD45.1) BM 15. For controls, we included mice reconstituted with a mixture of B7− and WT (CD45.1) BM or CD11c:DTA, B7− and WT BM only (Fig. 2A). In the resulting mixed [B7−/CD11c:DTA>WT ] BM chimeras, wt cDC are constantly ablated due to DTA expression. The cDC compartment of these animals thus consists exclusively of CD80−/−CD86−/− cDC. On the contrary, B cells and other hematopoetic cells in these animals are composed of both B7-proficient and -deficient cells, whereas nonhematopoetic cells, including the radio-resistant thymic epithelium, are exclusively of WT recipient genotype. Notably, the specific absence of CD80−/−CD86−/− from cDC in [B7−/CD11c:DTA>wt] BM chimeras had no effect on the percentages

of thymic Foxp3+ Treg out of single-positive CD4+ thymocytes (Fig. 2B). This corroborates earlier notions that mTEC and other, BM-derived APC can mediate the generation of nTreg in the thymus via B7 interactions 7, 19 and that thymic DC are dispensable for the generation of nTreg 14, 15. On the contrary, Roxadustat purchase peripheral Foxp3+ Treg in [CD11c:DTA>WT] chimeras, constitutively lacking cDC, and [B7−>WT] chimeras lacking CD80/CD86

expression on all BM-derived cells displayed markedly reduced Treg frequencies, when compared with [WT>WT] control chimeras (Fig. 2C and D). Moreover, importantly, the specific absence of CD80/CD86 on cDC, in the mixed [B7−/CD11c:DTA>wt] BM chimeras, also resulted in more than twofold reduction of peripheral Foxp3+ Treg. In contrast, mixed [B7−/WT>WT] BM chimeras retaining both B7-proficient and -deficient cDC displayed Mirabegron elevated percentages of Foxp3+ Treg, as compared with [B7−/CD11c:DTA>wt] chimeras (Fig. 2C and D). It is worth noting that the only difference between these two groups of mixed BM chimeras is the absence of CD80/CD86-proficient cDC in [B7−/CD11c:DTA>wt] chimeras. To substantiate our findings, we next generated mixed chimeras using BM of B7− mice (CD45.2) and CD11c-DTR mice (CD45.1) that allow for the conditional ablation of cDC 20. The resulting chimeras harbor a mixed DC-compartment consisting of DTx-sensitive WT DC and DTx-resistant B7− DC. DTx injection which leaves the chimeras only with CD80/CD86-deficient cDC resulted in a reduction of peripheral Treg (Fig. 2E).

8 ± 2 mmol/L Conclusion:  Routine use of citrate anticoagulation

8 ± 2 mmol/L. Conclusion:  Routine use of citrate anticoagulation in the setting of a long-term haemodialysis unit is safe and efficient. Point-of-care measurements of ionized calcium levels are critical to safely and successfully perform citrate anticoagulation. “
“The discovery of fibroblast growth factor-23 (FGF23) and its co-receptor α-klotho has broadened our understanding of mineral metabolism and led to a renewed research focus on phosphate homeostatic pathways in kidney disease. Expanding knowledge of these mechanisms, both in normal

physiology and in pathology, identifies targets for potential interventions designed to reduce the complications of renal disease, particularly the cardiovascular sequelae. FGF23 has emerged as a major α-klotho-dependent

endocrine regulator of mineral metabolism, functioning to find more activate vitamin D and as a phosphatonin. However, increasingly there is an appreciation CB-839 datasheet that klotho may act independently as a phosphate regulator, as well as having significant activity in other key biological processes. This review outlines our current understanding of klotho, and its potential contribution to kidney disease and cardiovascular health. Chronic kidney disease (CKD) represents a major and growing public health issue affecting 5–10% of the global population.[1] CKD-mineral bone disorder (CKD-MBD) describes the observations of disturbances of mineral metabolism (particularly calcium and phosphate), bone remodelling, Adenosine triphosphate and accelerated vascular and soft-tissue calcification seen in kidney disease.[2, 3] Control of phosphate flux is important in this process as well as being critical to the function of numerous essential biological processes.[4] Although a putative phosphate-sensing machinery has been identified in some single cell organisms,[5] the homologous sensor in vertebrates remains elusive. Nonetheless, extracellular phosphate levels do appear specifically regulated at the level of absorption through the intestine and excretion via the kidney. Thus in steady-state, the amount of phosphate

absorbed from the diet is equivalent to the amount excreted in the urine.[4] A number of hormones act, either directly or indirectly, to regulate the activity of key phosphate transporters to maintain phosphatehomeostasis in the face of fluctuation in supply (diet) and demand (cellular metabolism and bone mineralization) (Fig. 1). Klotho, originally identified as the anti-ageing protein, has become an important focus of research in nephrology because of its key role in phosphate homeostasis.[7, 8] The independent discoveries of fibroblast growth factor-23 (FGF23)[9, 10] and α-klotho,[7] have improved our understanding of mineral metabolism and phosphate handling. This review outlines the potential implications and therapeutic potential of this knowledge in kidney and cardiovascular disease.

25×104 in a final volume of 50 μL A total of 721 221 target cell

25×104 in a final volume of 50 μL. A total of 721.221 target cells were added (1×104 in 50 μL) to each well (quadruplicate wells were assayed per point) and the plate was centrifuged at 500 rpm for 1 min and incubated for 4 h at 37°C. At the end of this incubation period, 50 μL of assay buffer was added to each well. The substrate (50 μL/well) was added and the samples incubated in dark for 15 min. The plates were read using Synergy4 microplate reader (BioTeK® Instruments). Maximum cell lysis was determined by treating 1×104 target cells with 0.1% digitonin in assay buffer for 3 min at RT. Freshly harvested YTS, control vector-transduced YTS, and IQGAP1 shRNA-transduced YTS cells washed and resuspended

in 0.5% BSA in PBS (PBS-BSA). The cells were fixed for 10 min XL765 at room temperature in PBS containing 2% paraformaldehyde, washed three times in GDC-0068 concentration PBS-BSA, and permeabilized

with 0.1% Tween-20 in PBS-BSA for 5 min. The cells were washed three times in PBS-BSA and incubated with primary Ab against IQGAP1 or Alexa fluor phalloidin 488 for 45 min. The cells were washed and incubated with secondary goat anti-rabbit Alexa fluor 488 for 45 min. Cells were washed and staining was assessed (10 000 cells/sample) using a BD FACS Array system. First, the live cells were gated to exclude debris, and then the number of cells positive for Alexa fluor 488 was assessed within this population. The assay was performed according to the method described in 26. YTS cells were prelabeled with 1.5 μM Cell Tracker™ Green CMFDA (Invitrogen cat no. C2925) and target cells were labeled with 5 μM Cell Tracker™ Orange (Invitrogen cat no. C34551). The L-NAME HCl cells were combined

at an effector to target ratio of 2:1 and incubated for the indicated times. The samples were gently vortexed for 3 s at maximum vortex speed and immediately fixed with 2% PFA. Samples were run in triplicates and 30 000 events were counted for every replicate. The frequency of double-positive events was determined within the Cell Tracker™ Green-positive population using Summit V5.2.0.7477 software. The following gating strategy was used: First, the live cells were gated to exclude debris. Compensation adjustments were made on this population using single-positive cells stained for either of the two dyes. Gates were set to differentiate between the double positives, represented in G2, from the single positives and double negatives in the experimental cells. This research was supported by a grant from the Canada Institutes for Health Research (J. A. W.) and the Health Sciences Research Department (N. K.). The authors thank Qiujang Du for preparation of the shRNA-mir constructs and Monroe Chan for flow cytometry. Conflict of interest: The authors declare no financial or commercial conflict of interest. Detailed facts of importance to specialist readers are published as ”Supporting Information”.

, 2009a), however, might indicate the presence of a biofilm matri

, 2009a), however, might indicate the presence of a biofilm matrix in conventionally stained sections. Moreover, the investigation of novel stains specific for Temsirolimus clinical trial microbial biofilms is needed. Biofilm-specific biomarkers, such as antibodies, would also be desirable as a diagnostic tool; however, this is likely to be pathogen, not biofilm specific and possibly limited to certain anatomic

or surgically accessible sites. To date, no biofilm-specific antibodies are marketed. While there are some promising diagnostic technologies in development, it may be years until these diagnostics are certified for use in clinical laboratories (van Belkum et al., 2007). The guidelines presented in Table 4 are designed to provide a useful starting point for scientists and clinicians in distinguishing biofilm infections and a framework for discussion for further refinement and improvement by the larger biofilm and clinical community. Although providing evidence

from molecular markers that specific organisms are present, and microscopic evidence that a biofilm may be present, these may not be sufficient to demonstrate that the patient has a biofilm-associated disease without clinical signs and symptoms. Nonetheless, diagnostic guidelines are necessary to distinguish and verify a BAI as soon as possible, because evidence from CF suggests that biofilm infections that are left untreated are more recalcitrant to resolution (Döring et al., 2000; Döring & Høiby, 2004).

Additionally, diagnostic guidelines are essential for the evaluation DAPT of treatment regimes aimed at resolving BAI, because efficacy of antibiofilm treatment must indicate a significant reduction in bacteria as an outcome measure. BAI are difficult to diagnose because culture, although generally sufficient in acute disease, is not necessarily an accurate indicator of BAI. Thus, to investigate biofilms in vivo, identify an infectious etiology, or evaluate treatment, clear clinical signs and symptoms of BAI are also necessary. We have therefore combined criteria that biofilm microbiologists use to distinguish many microbial biofilm from planktonic modes of growth, with guidelines that clinicians use to evaluate laboratory results and clinical signs and symptoms of infections. These guidelines are useful not only for the clinician sampling the infection but also for clinical microbiologists handling these samples and emphasize that when there is a high clinical suspicion of infection, molecular tests should be ordered if possible in the face of culture-negative results to assess the possibility of BAI. “
“Leprosy is an infectious disease in which the clinical manifestations correlate with the type of immune response mounted to the pathogen, Mycobacterium leprae.

4b, upper panel) By

4b, upper panel). By IBET762 contrast, Ku70 staining was faint and nuclear staining was nearly undetectable in CD40L/IL-4-stimulated B cells (Fig. 4b, lower panel), a finding that coincided with the absence of proliferation

(Fig. 1b) and B-cell blast formation under these stimulatory conditions.[17] Full-blown proliferative responses as observed with CpG ODN stimulation might, therefore favour nuclear translocation of Ku70/80, but do not seem to be a prerequisite for RAG re-expression, because RAG-1 was detectable in CD40L/IL-4-stimulated B cells, whereas BCR stimulation failed to trigger RAG-1 expression (Fig. 2d). Having confirmed these molecular prerequisites for receptor revision we sought functional evidence for RAG activity. We postulated that re-expression of RAG in peripheral B cells enables Igκ/Igλ rearrangement in response to TLR9 ligation. To prove this hypothesis we purified Igκ+ B cells, and compared Igκ/Igλ expression in B cells stimulated with CpGPTO or CD40L/rhIL-4,

two stimuli that result in comparable cellular survival and autocrine Pirfenidone IL-6 but that differ in the extent of proliferation. Despite the absence of Igλ+ cells in sorted Igκ+ B cells (Fig. 5a), unstimulated and CD40L/rhIL-4-stimulated B cells, a small population of Igκ-negative Igλ+ B cells became detectable after TLR9 stimulation for 4–6 days (Fig. 5b). Moreover, co-expression of Igκ and Igλ on a subset of B cells (Fig. 5b) was interpreted as indicative for ongoing Igκ/Igλ rearrangement. Staining with the isotype control proved the specificity of the anti-Igλ staining (Fig. 5c). Importantly, the low frequency of the evolving Igλ+ population (Fig. 5b), e.g. for CpGPTO: 0·4 ± 0·2% (n = 6) and for CD40L/IL4: 0·03 ± 0·04% (n = 4) makes Igκ/Igλ rearrangement a rare event, a finding that is compatible with the overall low expression of TLR9-induced RAG-1 and selective accumulation of RAG-1 and Ku70 in a small B-cell subfraction. Taken together, these results provided the notion Nitroxoline that stimulation with TLR9-active ODN triggers RAG re-expression and consecutively catalyses LC rearrangements in a subfraction of B cells, so proving functional

integrity of TLR9-induced RAG proteins in these cells. The current understanding of receptor editing and revision implies that these processes must be initiated by binding of an autoantigen to the BCR. Of note, earlier reports described binding of CpGPTO to the BCR,[22] which raised the notion that CpGPTO could act as unselective BCR stimuli or might even mimic autoantigens. In a previous report we further demonstrated that stimulation of TLR9 with PTO-modified ODN selects IgM+ B cells for proliferation and differentiation.[17] As depicted in Fig. 6(a), CpGPTO-induced B-cell blasts originate from IgM+ CD27+ B cells because blast formation in response to CpGPTO is restricted to CD27+ and IgM+ B-cell fractions and is absent in CD27− and IgM− (class switched) B-cell fractions.

This last phenomenon was also observed when twofold, fourfold or

This last phenomenon was also observed when twofold, fourfold or eightfold lower concentrations of blocking peptides against pNF-κB p65 or pSTAT3 were used (data not shown). To assess the roles of NF-κB p65 and STAT3 in the later processes of cell differentiation (i.e. the final production of Ig), we sought to stimulate purified blood B cells with sCD40L + IL-10 while simultaneously blocking either one or both of the

transcription pathways using specific blocking peptides against pNF-κB p65 or pSTAT3. The pNF-κB p65 blocking peptide led to a modest, but significant, 20% decrease in pNF-κB p65. The anti-pSTAT3 peptide alone had nearly the same effect, resulting in an 18% reduction in pNF-κB p65. Together, the blocking peptides against pNF-κB p65 and pSTAT3 reduced NF-κB p65 phosphorylation Apoptosis inhibitor LDK378 by 28% (Fig. 8b). Reciprocally, the anti-pSTAT3 peptide significantly reduced pSTAT3 by 45% (Fig. 8c), while the anti-pNF-κB p65 peptide reduced it by 30%. Combined, these blocking peptides reduced pSTAT3 by 73%. IgA production was completely inhibited; however, phosphorylation of NF-κB and STAT3 was not blocked completely. These observations were probably due to neo-phosphorylation induced by other stimuli or by the oscillations in NF-κB signalling, as could have been

expected [32]. These data indicate that there is probably co-operation between Protein kinase N1 the various transcription factor pathways, and in particular, an NF-κB influence on the STAT3 pathway. Furthermore, these results suggest that sCD40L acts first on purified B cells, promptly activating the classical NF-κB pathway and inducing IL-10R expression (experiments and data not shown), which then renders the STAT3 pathway reactive to IL-10 signalling. We aimed

to elucidate some of the molecular pathways involved in providing purified B lymphocytes with the differentiation signals of non-cognate T cell surrogates, i.e. the classical sCD40L/CD40 + IL-10/IL-10R signals, leading to the skewed production of Ig towards IgA. We deliberately excluded from this investigation the addition of exogenous TGF-β, described classically as an IgA differentiation factor in a number of studies, on the basis of preliminary experiments (Fig. 2a and data not shown), having shown that TGF-β antagonized the differentiating role of sCD40L and IL-10 towards IgA class switch in this culture system. However, because these experiments were performed initially by culturing purified B lymphocytes in FCS-containing medium, the possibility that TGF-β eventually present in this serum may have biased our results was considered, as has been described, e.g. for the plasticity of T helper 17 (Th17) responses [33]. TGF-β1 induces IgA switching and secretion in stimulated B lymphocytes in mouse spleen. This has also been shown for IgG2b using mouse spleen B cells.

1 ml of each dilution was plated in duplicate onto Lowenstein-Jen

1 ml of each dilution was plated in duplicate onto Lowenstein-Jensen plates and incubated at 37 °C for 4 weeks. M. tuberculosis colonies on each plate were enumerated and the results were expressed as colony formation unit per organ. Pulmonary histopathological examination.  The lungs of the mice were fixed in 10% buffered formalin and paraffin-embedded. The paraffin-embedded tissue sections were prepared and stained with haematoxylin and eosin, and then analysed by a certified pathologist. Statistical analysis.  Data were expressed as means and standard deviations. Statistical significance between the treatment groups

was calculated using Student’s t-test, and a P-value of <0.05 was considered significant. T cells play a critical role in protective immunity against CH5424802 mw Acalabrutinib ic50 mycobacterial infection. IFN-γ ELISPOT assays were performed with the splenocytes isolated from immunized mice 2 weeks after the final immunization to analyse whether Ag85A DNA vaccine could induce specific T cell responses. As expected, mice subjected

to Ag85A DNA vaccination had a significantly increased amount of T cells that secreted IFN-γ in response to Ag85A protein than mice in control groups (P < 0.05), suggesting that Ag85A DNA immunization markedly augmented the splenic functional T cell response (Fig. 1). The production of IFN-γ from mice immunized with Ag85A DNA vaccine was significantly similar to those of saline group and plasmid vector pVAX1 group (P > 0.05), but higher

than that of M. vaccae vaccine group (P < 0.05). The production of IL-4 from mice immunized with Ag85A DNA vaccine was significantly lower than those of saline group and M. vaccae vaccine control group (P < 0.05), but comparable to that of the vector group (P > 0.05) (Fig. 2). One mouse was SPTBN5 dead in each of the plasmid vector group, RFP treatment group and M. vaccae vaccine group. The survival rates of these three groups were all 90%. Mice in other treatment groups were all 100% alive. More lymphocytes, extensive lung lesions, hyperaemia congestion in alveoli with damaged construction were observed in the lung sections from mice in the plasmid vector group and the RFP group. More foamoid cells and multi-nuclei giant cells, but fewer lymphocytes were observed in the lung sections from mice in the other therapeutic groups, and the alveoli profiles showed relatively clear and normal structures (Fig. 3). The amount of live bacteria in the lungs and spleens of mice 4 weeks after the completion of the 2-month chemotherapy were determined (Fig. 4). The CFUs from lung tissues in groups 1 to 7 were 7.43, 7.39, 6.25, 6.35, 6.08, 6.05 and 6.35 logs, respectively, and CFUs from spleen tissues were 6.36, 6.38, 5.45, 5.40, 5.36, 5.10 and 5.33 logs, respectively. Compared with the control groups, Ag85A DNA treatment alone or combined with RFP or PZA reduced the pulmonary and splenic bacterial loads by 1.03 and 1.38 logs, respectively.

This form of immune tolerance induction is now safer, more reliab

This form of immune tolerance induction is now safer, more reliably efficacious and better

understood than when it was first formally described in 1911. In this paper the authors aim to summarize the current state of the art in immunotherapy in the treatment of inhalant, venom and drug allergies, with specific reference to its practice in the United Kingdom. A practical approach has been taken, with reference to current evidence and guidelines, including illustrative protocols and vaccine schedules. A number of novel approaches and techniques are likely to change considerably the way in which we select and treat allergy patients in the coming decade, and these advances are previewed. CDK inhibition On 10 June 1911, Leonard Noon published the first short description of allergen-specific immunotherapy by injection [1]. His short

paper described increasing tolerance to conjunctival challenge testing with grass pollen extract. His work was completed by Freeman [2], who published a clinical description of improved hay fever symptoms in September of the same year. Between them, these papers described the hypothesis underpinning allergen immunotherapy, the production and standardization of pollen extracts, the use of subcutaneous injections, with short interval up-dosing and longer interval Ivacaftor datasheet maintenance, and adverse reaction due to overdose. They suggested confirmation of sensitization (by conjunctival challenge) prior to commencing therapy, titration of the starting dose, the choice of the single pollen Phleum pratense from a selection of grass pollen species, and also stated

that efficacy is proportional to the duration of prophylactic therapy. At face value it could be argued that these concepts have Unoprostone not changed in the last 100 years. However, the practice of allergen immunotherapy is now supported by a wealth of well-controlled studies, and novel formulations and routes of administration have been investigated. Nonetheless, the gold standard procedure of subcutaneous immunotherapy with P. pratense for hay fever remains alarmingly similar to that described a century ago. This review of allergen immunotherapy in the treatment of inhalant, venom and drug allergies will focus on patient selection and modalities of administration of this therapy, with specific emphasis on the practicalities of the safe delivery of this service in a specialist centre. Allergic rhinoconjuctivitis can be treated effectively with immunotherapy, as demonstrated in recent systematic reviews [3–5]. A wide range of aeroallergens, including pollens, house dust mite, animal danders, mould spores and some occupational allergens have been identified as causing allergic airways disease. Standardized allergen extracts are available and the treatment is currently administered either as subcutaneous injection immunotherapy (SCIT) or sublingual immunotherapy (SLIT), and these are discussed in the following sections. Indications.  Careful patient selection is paramount.

In contrast, adults with active pulmonary TB in a highly TB endem

In contrast, adults with active pulmonary TB in a highly TB endemic area in Indonesia had significantly lower plasma granulysin concentrations than did controls, these concentrations increasing after 2 months of anti-TB therapy to values similar to those of controls, and having increased even further after completion of anti-TB therapy. These changes in granulysin concentrations occurred predominantly in patients find more in whom IFN-γ negative T cells were expressed, suggesting that in TB the cellular sources of IFN-γ and granulysin are partly non-overlapping (14). Similar findings have

been reported for Italian children, the lowest concentrations having been found in TB patients who were PPD negative at the time of diagnosis (15), indicating the involvement of granulysin and IFN-γ in curative immune Ivacaftor research buy responses against Mtb. In chronic pulmonary TB, lung tissue biopsy has shown reduction in amounts of perforin and granulysin in relation to granzyme

A, while higher per cell expression of perforin and granulysin is associated with bacteriological control, suggesting that perforin and granulysin could be used as markers or correlates of immune protection in human TB (16). However, effective host mechanisms against Mtb infection are not well understood, this lack of understanding being a problem in regard to vaccine Unoprostone development and immunotherapy for TB. Moreover, so far there is limited information regarding the roles of IFN-γ and granulysin in recurrent TB. Therefore, the present study aimed to investigate whether granulysin and IFN-γ responses are associated with clinical disease in patients with newly diagnosed, relapsed and chronic pulmonary TB in northern

Thailand, where TB is endemic. One hundred and fifty-five pulmonary TB patients (aged 9 to 88 years) were recruited from the outpatient and inpatient clinics of Chiang Rai Hospital and Mae Chan Hospital, in the north of Thailand. These included 102 male and 53 female patients with newly diagnosed and previously treated pulmonary TB. Patients with extrapulmonary TB and pulmonary TB/HIV seropositive were excluded. All patients with pulmonary TB had clinical symptoms and a confirmed diagnosis on the basis of presence of acid-fast bacilli in sputum on microscopic examination, positive cultures of Mtb, medical history and chest radiographic findings. Patients were categorized according to World Health Organization criteria (1), which include ascertaining whether the patient has previously received TB treatment. The TB drug regimens were based on the recommendations of the National Tuberculosis Program, Ministry of Public Health, Thailand. Standard TB treatment drugs consist of streptomycin (S), isoniazid (H), rifampicin (R), pyrazinamide (Z) and ethambutol (E).

During human autoimmune diseases an impairment of Tregs has been

During human autoimmune diseases an impairment of Tregs has been observed, as well as the finding Silmitasertib research buy that these cells showed the capacity to block or reverse autoimmunity in a large number of experimental settings [37-41]. The evidence that Tregs can be induced when T cells are co-cultured in vitro with MSCs [6, 11] suggested this interaction as a further potential therapeutic target during

autoimmune diseases. At present, given that MSCs are already being utilized for the treatment of patients in clinical trials, a better understanding of the mechanisms mediating their effects in different autoimmune diseases is imperative. We have shown previously that MSCs isolated from SSc patients displayed an early senescent status, as shown by their reduced telomerase activity [17]. Senescence is characterized generally by both a decline in the cumulative number of cell population doublings and a limited lifespan, which are generally considered as age-related mechanisms [42]. In this study we showed a significantly decreased proliferation rate in SSc–MSCs already within the early passages when compared to HC, and this result was confirmed by the lower Ki67 gene expression, which is associated

strictly with cell proliferation [28]. The decreased Ki67 gene expression found in SSc cells confirms that a large MLN8237 cost proportion of SSc–MSCs are in growth-arrested status (G0 phase of the cell cycle). The specific unreplicative phenotype within SSc–MSCs was strengthened

by the observed increase of β-Gal activity when compared to HC, showing that these cells acquire a premature senescence habit. It should be considered that the local microenvironment in which Calpain these cells normally live could induce a senescent phenotype, and to understand this mechanism we exposed our cells to sublethal doses of doxorubicin, a chemotherapeutic drug, which is able to induce premature ageing, inducing DNA strand-breaking [18]. Furthermore, doxorubicin drives p53 protein accumulation [43], allowing time for faithful repair of DNA damage or, alternatively, eliminating cells with excessive DNA damage [44, 45]. P53 acts as transcriptional factor and activates directly the transcription of many genes, including p21. P21 is the first described downstream target of p53 and is an essential mediator of p53-dependent cell cycle arrest [46]. Paradoxically, several studies showed that these well-established DNA damage response systems, distinctive of somatic cells, appear to be lacking in stem cells [47]. The lack of p21 downstream activation after p53 accumulation permits bypassing the cellular quiescence induced specifically by p21, thus escaping senescence and acting as a sort of tolerance mechanism to genotoxic stresses [48, 49].