Low Levels Of Stimulation Research Articles

DRAK2 blockade leads to transplant tolerance by simultaneous deletion of effector T cells and enrichment of regulatory T cells (169.3)

Abstract DRAK2 is a serine/threonine kinase that has previously been shown to negatively regulate activation of T cells through the T cell receptor. Additionally, T cells lacking Drak2 are hypersensitive to low levels of stimulation, but are resistant to T cell mediated autoimmunity. Furthermore, Drak2-/- mice have no defects in viral immunity, making DRAK2 a novel target to replace current non-specific immunosuppressants used following transplantation. We hypothesized that Drak2 deficient T cells die after activation, and tested the ability of these T cells to respond to allogeneic stimulation. Using in vitro mixed lymphocyte reactions, Drak2-/- CD8+ T cells exhibited defects in accumulation after 5 days of allostimulation compared to wildtype T cells in vitro. Additionally, in vivo, allogeneic tumors grew uncontrolled by Drak2-/- T cells, and allogeneic skin graft rejection was significantly delayed. Overexpression of anti-apoptotic Bcl-xL in Drak2-/- T cells restored rejection of allogeneic tumors. Additionally, Drak2-/- mice had increased proportions of Tregs, and depletion of Tregs in a skin transplant model significantly enhanced Drak2-/- alloresponses. As a consequence of deletional tolerance, allogeneic memory was drastically reduced post transplant in Drak2-/- mice. Overall, these results demonstrate that DRAK2 plays a significant role in allograft responsiveness and highlight this kinase as a potential pharmacologic target in efforts to block allograft rejection.

Improving balance function using vestibular stochastic resonance: optimizing stimulus characteristics

Stochastic resonance (SR) is a phenomenon whereby the response of a non-linear system to a weak periodic input signal is optimized by the presence of a particular non-zero level of noise. Stochastic resonance using imperceptible stochastic vestibular electrical stimulation, when applied to normal young and elderly subjects, has been shown to significantly improve ocular stabilization reflexes in response to whole-body tilt; improved balance performance during postural disturbances and optimize covariance between the weak input periodic signals introduced via venous blood pressure receptors and the heart rate responses. In our study, 15 subjects stood on a compliant surface with their eyes closed. They were given low-amplitude binaural bipolar stochastic electrical stimulation of the vestibular organs in two frequency ranges of 1-2 and 0-30Hz over the amplitude range of 0 to ±700μA. Subjects were instructed to maintain an upright stance during 43-s trials, which consisted of baseline (zero amplitude) and stimulation (non-zero amplitude) periods. Measures of stability of the head and trunk using inertial motion unit sensors attached to these segments and the whole body using a force plate were measured and quantified in the mediolateral plane. Using a multivariate optimization criterion, our results show that the low levels of vestibular stimulation given to the vestibular organs improved balance performance in normal healthy subjects in the range of 5-26% consistent with the stochastic resonance phenomenon. In our study, 8 of 15 and 10 of 15 subjects were responsive for the 1-2- and 0-30-Hz stimulus signals, respectively. The improvement in balance performance did not differ significantly between the stimulations in the two frequency ranges. The amplitude of optimal stimulus for improving balance performance was predominantly in the range of ±100 to ±400μA. A device based on SR stimulation of the vestibular system might be useful as either a training modality to enhance adaptability or skill acquisition, or as a miniature patch-type stimulator that may be worn by people with disabilities due to aging or disease to improve posture and locomotion function.

Low Physiological Level of Stimulation Elicits Exocytosis, not by Ca 2+ Influx, but by Suppression of Ca 2+ Syntillas in Mouse Adrenal Chromaffin Cells

Catecholamine and neuropeptide exocytosis from adrenal chromaffin cells (ACCs) is controlled by sympathetic autonomic discharge. It has been thought that sympathetic discharge accomplishes this task exclusively by regulating Ca2+ influx through voltage-gated Ca2+ channels (VGCCs), which serves as a direct trigger for exocytosis. But our studies on spontaneous exocytosis in ACCs revealed the presence of Ca2+ syntillas, focal cytosolic transients mediated by ryanodine receptors (RYRs), and these had the surprising effect of inhibiting spontaneous exocytosis (Lefkowitz et al., 2009).Here we examine the role of syntillas under physiologic stimulation in ACCs using simulated action potentials (sAPs) designed to mimic native input at a frequency associated with basal sympathetic tone: 0.5 Hz. Stimulation at this frequency induces a general increase in the frequency and size of amperometric events comparable to that observed when syntillas were suppressed under spontaneous release conditions. Unexpectedly, we found that sAPs delivered at 0.5 Hz completely abolished Ca2+ syntillas within two minutes. Ca2+ arising from VGCCs was not enough to elevate the global [Ca2+]i as measured with fura-2. Hence, it appears that inhibition of syntillas by action potentials in ACCs is responsible for the increase in exocytosis at this level of stimulation.Funded by NIH grant HL21697 to JVW and AHA grant 0835580D to VD.Lefkowitz, J.J., K.E. Fogarty, L.M. Lifshitz, K.D. Bellve, R.A. Tuft, R. ZhuGe, J.V. Walsh, Jr., and V. De Crescenzo. 2009. Suppression of Ca2+ syntillas increases spontaneous exocytosis in mouse adrenal chromaffin cells. J Gen Physiol 134(4):267-280.

Dynamic interplay of excitatory and inhibitory coupling modes of neuronal L-type calcium channels

L-type voltage-gated calcium channels (LTCCs) have long been considered as crucial regulators of neuronal excitability. This role is thought to rely largely on coupling of LTCC-mediated Ca(2+) influx to Ca(2+)-dependent conductances, namely Ca(2+)-dependent K(+) (K(Ca)) channels and nonspecific cation (CAN) channels, which mediate afterhyperpolarizations (AHPs) and afterdepolarizations (ADPs), respectively. However, in which manner LTCCs, K(Ca) channels, and CAN channels co-operate remained scarcely known. In this study, we examined how activation of LTCCs affects neuronal depolarizations and analyzed the contribution of Ca(2+)-dependent potassium- and cation-conductances. With the use of hippocampal neurons in primary culture, pulsed current-injections were applied in the presence of tetrodotoxin (TTX) for stepwise depolarization and the availability of LTCCs was modulated by BAY K 8644 and isradipine. By varying pulse length and current strength, we found that weak depolarizing stimuli tend to be enhanced by LTCC activation, whereas in the course of stronger depolarizations LTCCs counteract excitation. Both effect modes appear to involve the same channels that mediate ADP and AHP, respectively. Indeed, ADPs were activated at lower stimulation levels than AHPs. In the absence of TTX, activation of LTCCs prolonged or shortened burst firing, depending on the initial burst duration, and invariably augmented brief unprovoked (such as excitatory postsynaptic potentials) and provoked electrical events. Hence, regulation of membrane excitability by LTCCs involves synchronous activity of both excitatory and inhibitory Ca(2+)-activated ion channels. The overall enhancing or dampening effect of LTCC stimulation on excitability does not only depend on the relative abundance of the respective coupling partner but also on the stimulus intensity.

Shear-dependent suppression of platelet thrombus formation by phosphodiesterase 3 inhibition requires low levels of concomitant Gs-coupled receptor stimulation

Phosphodiesterase (PDE)3 inhibitors exert potent antiplatelet effects through maintaining elevated intracellular cyclic adenosine monophosphate levels, but do not prolong bleeding time. To resolve this discrepancy, we hypothesised that PDE3 inhibitors effectively suppress shear-induced platelet thrombus formation initiated by the interaction of the platelet receptor GPIb/V/IX with its ligand, von Willebrand factor (VWF), since arterial thrombosis is more dependent on shear stress as compared with haemostatic plug formation. To test the hypothesis, we compared the in vitro effects of K-134 (a PDE3 inhibitor), tirofiban (a GPIIb/IIIa inhibitor) and acetylsalicylic acid (ASA) on ristocetin-induced platelet aggregation and platelet thrombus formation on VWF or collagen surfaces under flow conditions. K-134 inhibited GPIIb/IIIa-dependent platelet aggregation to the same extent as tirofiban and more potently than ASA. Likewise, K-134 and tirofiban effectively inhibited stable platelet thrombus formation (platelet firm adhesion and subsequent aggregation) on the VWF or collagen surface under high shear, but ASA only inhibited aggregation. Notably, inhibition by K-134 became evident only when a low concentration of PGE1 was present. These inhibitors did not block shear-induced initial platelet contact with VWF via GPIb/V/IX. In contrast, under low shear, the inhibitory effects of K-134 on platelet aggregation on the collagen surface were lower than tirofiban or ASA. The observed shear-dependent suppression of platelet thrombus formation by PDE3 inhibitor in the presence of low levels of adenylate cyclase stimulator may contribute to high therapeutic benefit with low risk of bleeding.

Relationship between gap detection thresholds and loudness in cochlear-implant users

Gap detection threshold (GDT) is a commonly used measure of temporal acuity in cochlear-implant (CI) recipients. This measure, like other measures of temporal acuity, shows considerable variation across subjects and also varies across stimulation sites within subjects. The aims of this study were (1) to determine whether across-site variation in GDTs would be reduced or maintained with increased stimulation levels; (2) to determine whether across-site variation in GDTs at low stimulation levels was related to differences in loudness percepts at those same levels; and (3) to determine whether matching loudness levels could reduce across-site differences in GDTs. Thresholds and maximum comfortable loudness levels were measured in postlingually deaf adults using all available sites in their electrode arrays. All sites were then surveyed at 30% of the dynamic range (DR) to examine across-site variation. Two sites with the largest difference in GDTs were then selected and for those two sites GDTs were measured at multiple levels of the DR (10%, 30%, 50%, 70%, and 90%). Stimuli consisted of 500 ms trains of symmetric-biphasic pulses, 40 μs/phase, presented at a rate of 1000 pps using a monopolar (MP1+2) electrode configuration. To examine perceptual differences in loudness, the selected sites were loudness-matched at the same levels of the DR. Variations in GDTs and loudness patterns were observed across stimulation sites and across subjects. Variations in GDTs across sites tended to decrease with increasing stimulation levels. For the majority of the subjects, stimuli at a given level in %DR were perceived louder at sites with better GDTs than those presented at the same level in %DR at sites with poorer GDTs. These results suggest that loudness is a contributing factor to across-site variation in GDTs and that CI fittings based on more detailed loudness matching could reduce across-site variation and improve perceptual acuity.

Effects of Stimulation Level and Electrode Pairing on the Binaural Interaction Component of the Electrically Evoked Auditory Brain Stem Response

The purpose of this study was to investigate the effects of stimulation level and electrode pairing on the binaural interaction component (BIC) of the electrically evoked auditory brain stem response (EABR) in Nucleus cochlear implant (CI) users. Ten postlingually deafened adult CI users participated in this study. EABRs were measured using loudness balanced, biphasic current pulses presented in the left monaural, right monaural, and bilateral stimulation conditions. BICs were computed based on measures of the EABR obtained for each subject by pairing the electrode 12 (of 22 intracochlear electrodes) in the right ear with each of 11 electrodes spaced across the electrode array in the left ear. The effect of stimulation level on the amplitude of the BIC was investigated by measuring growth functions of the BIC from six subjects. The effect of electrode pairing on the amplitude of the BIC was studied at high stimulation levels in 10 subjects and at low stimulation levels in seven subjects. The high stimulation level was chosen as the 90% point of the subject's dynamic range (DR) or the highest stimulation level in which the electrophysiologic recordings were not contaminated by muscle artifacts. The low stimulation level was chosen as a level that was 10% point of subject's DR higher than the BIC threshold for six of these seven subjects. For one subject, BIC thresholds were not available and the low stimulation level was referred to the 70% point of subject's DR. BICs were successfully recorded from all 11 interaural electrode pairs for a majority of subjects tested at both stimulation levels. BIC amplitudes increased with stimulation level. The effect of stimulation level on latencies of the BIC was less robust. At high stimulation levels, BIC amplitudes did not change significantly as the stimulating electrode used in the left ear was systematically varied. When low stimulation levels were used, BIC amplitude was maximal for interaural electrode pairs with similar intracochlear positions and decreased when the offset between interaural electrodes increased. This study demonstrates that stimulation level affects amplitudes of the BIC response. It is possible to record the BIC of the EABR in bilateral CI users even from interaural electrode pairs that have large interaural offsets. This finding suggests that when high-level stimuli are used, there is a broad pattern of current spread within the two cochleae. At lower stimulation levels, the spread of excitation within the cochlea is reduced making the effect of electrode pairing on the amplitude of the BIC more pronounced.

Auditory Brain Stem Responses Evoked by Different Chirps Based on Different Delay Models

A cochlear delay model has previously been proposed for the construction of a chirp stimulus in order to compensate for the temporal dispersion in the auditory periphery. The large intersubject variability in the model data suggests that a chirp constructed from the average model data will not be able to compensate equally well for the temporal dispersion in all normal-hearing subjects. For the recording of the auditory brain stem response (ABR), it has been suggested that the most efficient chirp for generating the largest response amplitude changes in duration with level, indicating that the delay model exhibits a latency change with frequency, which becomes larger at lower levels. To investigate in normal-hearing subjects how the ABR varies in response to five different chirps and to study how the efficiency of each chirp changes with stimulus level. A click and five chirps of different durations and constructed from the proposed delay model were designed with identical amplitude spectra. The six stimuli were used to record the ABR from 50 normal-hearing test subjects using a quasi-simultaneous stimulation technique at 50 and 30 dB nHL. The ABR recordings were evaluated by the peak-to-trough amplitude and the peak latency. For the test group the following level effect was demonstrated: at 50 dB nHL the largest response amplitude was provided by a shorter chirp, whereas at 30 dB nHL the largest response amplitude was provided by a longer chirp. There is, however, large variability as to which of the five chirps generated the largest response in each individual subject, but at the two levels of stimulation, the best chirps were significantly correlated across the test group. All five chirps generated significantly larger ABRs than the click, but at 30 dB nHL the gain in response amplitude by using the chirps instead of the click was larger than at 50 dB nHL. A chirp that evokes the largest broadband ABRs in normal-hearing subjects changes in duration with level-that is, being relatively short at higher levels (50 dB nHL) and relatively long at lower levels and near the threshold. However, the changes in amplitude in response to chirps of different durations are not very large, and it is therefore uncertain whether the outcome from using such chirps actually would outweigh the instrumental complexity of implementation. It appears that the largest advantage of using the chirp over the click is found at the lower levels of stimulation.

Exploring impulse buying and variety seeking by retail shoppers: towards a common conceptual framework

Impulse buying and variety seeking are both low-effort feelings-based behaviours with similar psychological origins. However, there is little research exploring the common sociopsychological processes regulating these behaviours. This gap is addressed with a conceptual framework incorporating the discrepancy between actual and optimum stimulation levels as the driver of both the behaviours, and self-monitoring as the moderator of interpersonal influences on these. Findings from a field-survey-based study with retail shoppers show that both the behaviours are responses to exploratory urges triggered by lower stimulation levels. Moreover, high self-monitors exhibit greater impulsiveness in private and seek greater variety in public compared to low self-monitors. The paper concludes with a discussion on its conceptual and managerial contribution along with some of its limitations and directions for future research.

Ordinary variations in human maternal caregiving in infancy and biobehavioral development in early childhood: A follow‐up study

Rodent models of early caregiving find that pups reared by dams providing low levels of early stimulation subsequently display heightened stress reactivity and social aggression. We examined these effects in humans by investigating the effects of early caregiving on markers of biobehavioral development at ages 2 and 3 years. This study extended the findings reported by Hane and Fox (Hane and Fox [2006] Psychol. Sci. 17: 550-556) in which 185 mothers and infants were observed and scored for variations in maternal caregiving behavior (MCB) at age 9 months. Relative to young children who received high-quality MCB in infancy, those who received low-quality MCB showed significantly higher socially inhibited behavior with adults, right frontal electroencephalographam (EEG) asymmetry, aggressive play, and maternal reported internalizing behavior problems and anger proneness. These effects were independent of early temperamental reactivity. Results parallel rodent models and demonstrate that ordinary variations in MCB influence stress reactivity and social behavior in young children.

Drak2 is required for T cell mediated allogeneic transplant rejection (145.9)

Abstract Drak2 is a serine threonine kinase that has previously been shown to negatively regulate activation of T cells through the T cell receptor. Additionally, T cells lacking Drak2 are hypersensitive to low levels of stimulation, but are surprisingly resistant to autoimmunity in an EAE model. Since it has been hypothesized that Drak2 deficient T cells die after activation, we tested the ability of these T cells to respond to allogeneic stimulation, which would mimic transplantation from an allogeneic donor. Using in vitro mixed lymphocyte reactions, Drak2-/- CD8+ T cells responded less to allogeneic stimulation compared to wildtype T cells when analyzed by CFSE dilution. Additionally, allogeneic tumors were used to determine the role of Drak2 during an in vivo allogeneic transplant. Rag2-/- gamma C-/-mice adoptively transferred with purified Drak2-/- T cells were not able to clear allogeneic tumors contrary to wildtype T cell recipients. Additionally, transgenic Bcl-xL expression in Drak2-/- T cells rescued the alloresponse, illustrated by restored ability to clear allogeneic tumors. Next, we aim to determine if Drak2 blockade is sufficient to prevent rejection in a pancreatic islet transplant model.

Progesterone Function in Human Endometrium: Clinical Perspectives

Progesterone is essential for endometrial receptivity and successful establishment of pregnancy. Either an insufficient progesterone concentration or an insufficient response to progesterone, therefore can lead to infertility and pregnancy loss. Assessment of the role that either progesterone insufficiency or inadequate progesterone response plays in human reproductive failure has been difficult to assess because serum progesterone concentrations fluctuate markedly, limiting the ability to characterize sufficiency of progesterone, and there are no highly reliable markers of endometrial function available. Recent evidence demonstrates exquisite sensitivity of normal endometrium to very low levels of progesterone stimulation, suggesting that progesterone insufficiency should not be a common cause of reproductive failure. Further evidence suggests that women with endometriosis, and possibly polycystic ovarian syndrome, have an altered progesterone response, which may explain some of the clinical features of these disorders and supports the hypothesis that progesterone resistance underlies some cases of human reproductive failure.

How many people should be in the urban forest? A comparison of trail preferences of Vienna and Sapporo forest visitor segments

Differences in trail preferences for social conditions of visitors to forests in Vienna and Sapporo were investigated in 2006 using a standardised image-based stated choice approach. On-site visitors to two comparable peri-urban forests – the Lobau Forest in Vienna, Austria ( n=373), and the Nopporo Forest in Sapporo, Japan ( n=256) – evaluated the same sets of computer manipulated images depicting 128 trail scenarios with different levels of social stimulation. Latent class segmentations, in three sub-segments of similar sizes, differentiated by partly opposite preferences for social conditions, were derived for both samples. A positive contribution of social stimulation to preferences was found for about 17% of Nopporo and 9% of Lobau respondents, while for close to 50% of Lobau respondents and 38% of Nopporo respondents very low levels of social stimulation were preferred. The results indicate that urban forests should be managed for users with a desire for low social densities as well as a denser social setting providing some levels of social stimulation.

All three classes of CpG ODNs up-regulate IP-10 gene in pigs

The analysis of CpG ODN induced innate immune responses in different animal species has shown substantial similarities and differences in levels and types of induced cytokines profile. The objectives of these studies were to identify innate immune biomarkers activated by three classes of CpG ODNs in pigs. For this purpose, we investigated the kinetics of innate immune responses in immune cells from pigs following in vitro and in vivo stimulation with CpG ODNs. The mRNA expression of cytokine and chemokine genes were assayed by SYBR @ green based quantitative real time PCR. A-class CpG ODN induced significant but transient levels of IFN-γ, IL-12 (P40), IL-6, IL-4 and TNF-α mRNA, C-class CpG ODN induced significant level of IFN-γ, IFN-α and IL-12 mRNA and the lowest level of IL-4 (Th-2 type) mRNA. A very low level of some cytokines stimulation was observed by GC ODNs. It is noteworthy, that IL-12 (P35) mRNA was significantly stimulated by B-class GpC ODN 7909. Interestingly, all classes of CpG ODNs induced significant level of IP-10 at 12 h post stimulation. These in vitro and in vivo observations suggest that interferon-γ inducible protein 10 (IP-10) may be a reliable biomarker for immune activity induced by CpG ODNs in pigs.

Towards a polariton-based light emitter based on non-polar GaN quantum wells

A polariton-based light emitter is a extraordinary concept as an alternative to a light-emitting diode (LED) or laser diode. The physics of a polariton laser is fundamentally different from the spontaneous emission process of an LED or the inversion and stimulated emission process of a laser diode. The rapid decay and emission from this polariton–exciton state bypasses the normal irreversible spontaneous emission and associated non-radiative decay mechanisms. An AlGaN/AlN nucleation bilayer was employed on r -plane sapphire to deposit non-polar GaN quantum wells embedded in an AlGaN-based cavity surrounded by top and bottom distributed Bragg reflectors (DBRs). The reflectance data show that the exciton and photon states can be tuned (by changing the angle of the sample) to the same energy. The characteristic strong coupling was observed in the reflectance data where the states of the exciton and photon do not overlap; rather they split into an upper polariton state and a lower polariton state. The photoluminescence (PL) showed a strong emission at a low stimulation level at a similar energy and angle.

Developmental effects on dopamine projections and hippocampal cell proliferation in the rodent model of postweaning social and physical deprivation can be triggered by brief changes of environmental context

Periadolescence is a critical period during which environmental stimuli modulate developmental neural plasticity. This includes the density of mesolimbic dopamine (DA) projections and the mitotic dynamic in the hippocampal dentate gyrus, both involved in central structures for emotional and cognitive functioning. Behavioural tests suggest that even short periods of stimulation can have lasting developmental effects on cognitive and emotional measures. We therefore exposed animals kept in isolation to brief daily context changes during periadolescence (postnatal days 30–60). We assessed the effects on neural development after animals had reached adulthood at postnatal day 90 by measuring the density of dopamine fibres in the medial prefrontal cortex (PFC), nucleus accumbens (core and shell), olfactory tubercle, and amygdala (basolateral and central), and by labelling mitoses in the dentate gyrus by BrdU. In experimental animals as compared to deprived controls, dopamine fibre densities were increased in the PFC and basolateral amygdala, decreased in the central amygdala, but not altered in the ventral striatum. Hippocampal cell proliferation was decreased. These results show that even a low level of experimental sensory stimulation during periadolescence triggers neural developmental processes, with lasting effects into adulthood.

Information propagation from IP 3 to target protein: A combined model for encoding and decoding of Ca 2+ signal

It is well known that information is encoded in the frequency or amplitude of Ca 2+ signal and then decoded by target protein. However, few models considered both the encoding and decoding procedures of Ca 2+ signal. In this work, a minimal Li–Rinzel model is coupled with a phosphorylation–dephosphorylation cycle model, which is used to investigate information transmissions from inositol 1,4,5-trisphosphate (IP 3) to target proteins and their relations. We found that the mean target protein activity increases with the IP 3 concentration, and at a low level of stimulation, the target protein can be more efficiently activated by an oscillatory signal than a constant signal of the same average calcium if Ca 2+ acts cooperatively on the kinase. The internal noise resulting from the finite system size is also taken into account in the combined model.

Conditional targeting of C-terminal Src kinase (Csk) in NK cells (135.2)

Abstract Csk is a key negative regulator of Src-family kinases and has been shown to be a strong inhibitor of immunoreceptor signalling in T cells and granulocytes. Our hypothesis is that an increase in Src kinase activity might take place in NK cells following the elimination of Csk, resulting in an enhanced cellular response even at low levels of stimulation. We aim to establish the role of Csk in NK cells using conditional knockout mice. A transgenic mouse has been developed where the Csk gene is flanked by LoxP (floxed) sites. Crossing Csk floxed transgenic mice with transgenic mice expressing Cre recombinase under the control of a human CD2 gene (hCD2-iCre) will enable the deletion of the Csk gene in a tissue-specific manner. The ROSA26 reporter gene system suggests that Cre deletes the floxed gene in approximately 30% of splenic NK cells and, as reported before, in the vast majority of T cells and B cells. Intracellular staining for Csk demonstrates a correlation between Cre targeting of the ROSA26 locus and the target locus. There is a reduction in the number of lymphocytes in the Csk knockout (KO) mouse. More specifically, there is a decrease in B cells, suggesting a role for Csk in B cell development. However, no obvious phenotype is detected in NK cells. Ongoing studies of NK cell functions will be presented.

The role of Drak2 in T-cells during an alloresponse (141.7)

Abstract Drak2 is a serine threonine kinase that has previously been shown to negatively regulate activation of T cells through the T cell receptor. Additionally, T cells lacking Drak2 are hypersensitive to low levels of stimulation, but are surprisingly resistant to autoimmunity in an EAE model. Since it has been hypothesized that Drak2 deficient T-cells die after activation, I tested the ability of these T cells to respond to allogeneic stimulation, which would mimic transplantation from an allogeneic donor. Using in vitro mixed lymphocyte reactions, Drak2-/- CD8+ T-cells responded less to allogeneic stimulation compared to wildtype T-cells when analyzed by CFSE dilution. Additionally, allogeneic tumors were used to determine the role of Drak2 during an in vivo allogeneic transplant. Contrary to in vitro results, Drak2-/- mice were able to clear the allogeneic tumor in vivo. Subsequently, T cells isolated from Drak2-/- mice which had cleared an allogeneic tumor displayed proliferation defects when re-challenged in vitro. In the future adoptive transfers of Drak2-/- T-cells into mice lacking B, T, and NK cells will be done to address the specific role of Drak2 in T cell mediated allorejection.

IRF-4-Binding Protein Inhibits Interleukin-17 and Interleukin-21 Production by Controlling the Activity of IRF-4 Transcription Factor

The T helper 17 (Th17) cell lineage is important in inflammatory and autoimmune responses, via its ability to produce interleukin-17 (IL-17) and IL-21. Given the potentially deleterious effects of Th17 cells, their generation needs to be strictly controlled. IRF-4 is a transcription factor that has recently emerged as a key regulator of Th17 cell differentiation. Here, we showed that mice deficient in a previously isolated protein, IBP (IRF-4-binding protein), rapidly developed rheumatoid arthritis-like joint disease and large-vessel vasculitis. The pathology was associated with an enhanced responsiveness of T cells to low levels of stimulation and with the inappropriate synthesis of IL-17 and IL-21. IBP sequestered IRF-4 and prevented it from targeting the transcriptional regulatory regions of the genes that encode IL-17 and IL-21. Thus, IBP appears to be important in preventing T cell-mediated autoimmunity by ensuring that the production of IL-17 and IL-21 does not occur in response to self-antigens.