T lymphocyte-mediated antiviral immune responses in mice are diminished by treatment with monoclonal antibody directed against the interleukin-2 receptor

Bu‑Shen‑Ning‑Xin decoction suppresses osteoclastogenesis by modulating RANKL/OPG imbalance in the CD4+ T lymphocytes of ovariectomized mice

Postmenopausal osteoporosis (PMO) has been recognized as an inflammatory condition. CD4⁺ T cells serve a key role in the interaction between bone metabolism and the immune system. Bu-Shen-Ning-Xin decoction (BSNXD), a traditional Chinese medicine, has been ultilized as a remedy for PMO. In the present study, the aim was to investigate the immune modulatory effects of BSNXD on CD4⁺ T cells, receptor activation of nuclear factor κB ligand (RANKL)/osteoprotegerin (OPG) imbalance, skeletal parameters and osteoclastogenesis. Ovariectomized (OVX) mice were treated with a series of concentrations of BSNXD and then autopsied. The bone phenotype was analyzed by micro computed tomography. CD4⁺ T cells were isolated and their percentage was measured using flow cytometry (FCM). RANKL and OPG expression by the CD4⁺ T cells at the transcriptional and translational levels were quantified by reverse transcription-quantitative polymerase chain reaction, ELISA and FCM. CD4⁺ T cells were cultured with blood serum derived from BSNXD-treated OVX mice (BSNXD-derived serum) and the apoptosis rate was quantified by FCM. CD4⁺ T cells were co-cultured with bone marrow-derived macrophages and exposed to BSNXD-derived serum to whether CD4⁺ T cells are involved in BSNXD-modulated osteoclastogenesis and the results were quantified via tartrate-resistant acid phosphatase staining. The results revealed that BSNXD ameliorated OVX-induced bone loss, prevented the expansion of CD4⁺ T cells and restored the RANKL/OPG imbalance in the CD4⁺ T cells of OVX mice. In vitro, BSNXD-derived serum promoted the apoptosis of CD4⁺ T cells. The co-culture system demonstrated that CD4⁺ T cells from OVX mice increase osteoclastogenesis, while this effect was suppressed by BSNXD administration. The findings of the study collectively suggest that BSNXD exerts an immunoprotective effect on the bone phenotype of OVX mice by ameliorating RANKL/OPG imbalance in CD4⁺ T cells and attenuating osteoclastogenesis.

Interleukin 2: from immunostimulation to immunoregulation and back again

Interleukin 2 (IL-2) was one of the first cytokines to be discovered. However, the complex role of IL-2 and its receptor in the regulation of immune responses is only now emerging. This review explores the various signals triggered by IL-2 and discusses their translation into biological function. A model is outlined that accommodates the seemingly contradictory functions of IL-2, and explains how one cytokine can be an essential T-cell growth and differentiation factor and yet also be indispensable to maintain peripheral tolerance.

Protracted course of lymphocytic choriomeningitis virus WE infection in early life: induction but limited expansion of CD8+ effector T cells and absence of memory CD8+ T cells

Viral infections in human infants frequently follow a protracted course, with higher viral loads and delayed viral clearance compared to viral infections in older children. To identify the mechanisms responsible for this protracted pattern of infection, we developed an infant infection murine model using the well-characterized lymphocytic choriomeningitis virus (LCMV) WE strain in 2-week-old BALB/c mice. In contrast to adult mice, in which viral clearance occurred as expected 8 days after infection, LCMV titers persisted for several weeks after infection of infant mice. LCMV-specific effector CD8(+) T cells were elicited in infant mice and fully functional on day 7 but rapidly waned and could not be recovered from day 12 onwards. We show here that this results from the failure of LCMV-specific CD8(+) T cells to expand and the absence of protective LCMV-specific memory CD8(+) T cells. Under these early life conditions, viral control and clearance are eventually achieved only through LCMV-specific B cells that contribute to protect infant mice from early death or chronic infection.

Cutting edge: Paracrine, but not autocrine, IL-2 signaling is sustained during early antiviral CD4 T cell response

IL-2 is expressed predominantly by activated T cells, and regulates T cell function by activating, via its receptor, the latent transcription factor STAT5. This signaling can occur in either a paracrine (between cells) or an autocrine (same cell) manner, although the kinetics by which these two signaling modes operate during in vivo T cell responses are unknown. In the current study, IL-2 expression and signaling in a clonotypic population of antiviral CD4+ T cells was analyzed by flow cytometry during the initial 24 h of priming. IL-2 expression and STAT5 activation peaked in parallel, but surprisingly, were almost completely mutually exclusive. Thus, only paracrine IL-2 signaling could be observed. As an additional indication of the efficiency of paracrine IL-2 signaling, polyclonal CD4+CD25+Foxp3+ regulatory T cells displayed detectable STAT5 activation under steady-state conditions, which was strongly enhanced by neighboring IL-2-expressing antiviral CD4 cells.

Direct Stimulation of T Cells by Type I IFN Enhances the CD8+T Cell Response during Cross-Priming

Type I IFN (IFN-alphabeta), which is produced rapidly in response to infection, plays a key role in innate immunity and also acts as a stimulus for the adaptive immune response. We have investigated how IFN-alphabeta induces cross-priming, comparing CD8+ T cell responses generated against soluble protein Ags in the presence or absence of IFN-alphabeta. Injection of IFN-alpha was found to prolong the proliferation and expansion of Ag-specific CD8+ T cells, which was associated with marked up-regulation of IL-2 and IL-15 receptors on Ag-specific cells and expression of IL-15 in the draining lymph node. Surprisingly, neither IL-2 nor IL-15 was required for IFN-alpha-induced cross-priming. Conversely, expression of the IFN-alphabetaR by T cells was shown to be necessary for effective stimulation of the response by IFN-alpha. The finding that T cells represent direct targets of IFN-alphabeta-mediated stimulation reveals an additional mechanism by which the innate response to infection promotes adaptive immunity.

IL-2 is not required for the initiation of CD8 T cell cycling but sustains expansion

Based primarily on in vitro data, IL-2 is believed to be the key cytokine for initiation of the cell cycle of activated T cells. However, the role of IL-2 remains unresolved for T cell responses in vivo. We examined whether the absence of IL-2-mediated signaling in CD8 T cells affected initiation of proliferation. Our results conclusively demonstrated that initial division of Ag-specific CD8 T cells following priming was IL-2 independent, regardless of the context in which Ag was presented. In contrast, the latter stage of the proliferative phase was IL-2-dependent, particularly in nonlymphoid tissues. Thus, activated CD8 T cells initially undergo IL-2-independent proliferation, but reach a critical juncture where the requirement for IL-2 as a growth factor gains prominence.

Cytokine control of memory T-cell development and survival

Evidence has accumulated that cytokines have a fundamental role in the differentiation of memory T cells. Here, we follow the CD8+ T cell from initial activation to memory-cell generation, indicating the checkpoints at which cytokines determine the fate of the T cell. Members of the common cytokine-receptor gamma-chain (gammac)-cytokine family--in particular, interleukin-7 (IL-7) and IL-15--act at each stage of the immune response to promote proliferation and survival. In this manner, a stable and protective, long-lived memory CD8+ T-cell pool can be propagated and maintained.

Essential role for IL-2 in the regulation of antiviral extralymphoid CD8 T cell responses

IL-2 is a cytokine produced primarily by activated T cells and is thought to be the quintessential T cell growth factor. The precise role of IL-2 in the regulation of CD8 T cell responses to foreign Ag in vivo however remains enigmatic. Using an adoptive transfer system with IL-2- or IL-2R-deficient TCR transgenic CD8 T cells and MHC class I tetramers, we demonstrated that the expansion of antiviral CD8 T cells in secondary lymphoid tissues was IL-2 independent, whereas IL-2 played a more significant role in supporting the continued expansion of these cells within nonlymphoid tissues. Paradoxically, autocrine IL-2 negatively regulated the overall magnitude of the CD8 T cell response in nonlymphoid tissues via a Fas-independent mechanism. Furthermore, autocrine IL-2 did not regulate the contraction or memory phase of the response. These experiments identified a novel role for IL-2 in regulation of antiviral CD8 T cell responses and homeostasis in nonlymphoid tissues.

Simian virus 40 large-T-antigen-specific rejection of mKSA tumor cells in BALB/c mice is critically dependent on both strictly tumor-associated, tumor-specific CD8(+) cytotoxic T lymphocytes and CD4(+) T helper cells

Protective immunity of BALB/c mice immunized with simian virus 40 (SV40) large T antigen (TAg) against SV40-transformed, TAg-expressing mKSA tumor cells is critically dependent on both CD8(+) and CD4(+) T lymphocytes. By depleting mice of T-cell subsets at different times before and after tumor challenge, we found that at all times, CD4(+) and CD8(+) cells both were equally important in establishing and maintaining a protective immune response. CD4(+) cells do not contribute to tumor eradication by directly lysing mKSA cells. However, CD4(+) lymphocytes provide help to CD8(+) cells to proliferate and to mature into fully active cytotoxic T lymphocytes (CTL). Depletion of CD4(+) cells by a single injection of CD4-specific monoclonal antibody at any time from directly before injection of the vaccinating antigen to up to 7 days after tumor challenge inhibited the generation of cytolytic CD8(+) lymphocytes. T helper cells in this system secrete the typical Th-1 cytokines interleukin 2 (IL-2) and gamma interferon. Because in this system TAg-specific CD8(+) cells secrete only minute amounts of IL-2, it appears that T helper cells provide these cytokines for CD8(+) T cells. Moreover, this helper effect of CD4(+) T cells in mKSA tumor rejection in BALB/c mice does not simply improve the activity of TAg-specific CD8(+) CTL but actually enables them to mature into cytolytic effector cells. Beyond this activity, the presence of T helper cells is necessary even in the late phase of tumor cell rejection in order to maintain protective immunity. However, despite the support of CD4(+) T helper cells, the tumor-specific CTL response is so weak that only at the site of tumor cell inoculation and not in the spleen or in the regional lymph nodes can TAg-specific CTL be detected.

Activated, cytotoxic CD8(+) T lymphocytes contribute to the pathology of asthma death

This study investigates the presence of CD8(+) T lymphocytes and their possible association with viral infection in bronchi of victims of fatal asthma. Postmortem samples from the peribronchial region of the lung were obtained from seven patients who died an asthma death (AD), seven asthmatic patients who died of unrelated causes (AUC), and seven postmortem cases with no history of lung disease (control subjects). Using immunohistochemical techniques, the CD8(+) cytotoxic T-cell population in peribronchial tissue was characterized in three patient groups. The percentage of CD8(+) cells expressing the activation marker CD25 was higher in the AD group than in both the AUC and control groups (11.91 +/- 1.92% versus 3.93 +/- 1.63% and 1.09 +/- 0.56%, respectively (p < 0.001). Perforin expression, a marker of cytotoxicity, was highest in the AD group (9.16 +/- 1.5%) compared with 1.39 +/- 0.9; 1.8 +/- 0.6% in the AUC and control groups respectively (p < 0.001). Expression of interleukin-4 (IL-4) and interferon gamma (IFN-gamma) by CD8(+) T cells was higher in the AD group than the control group (p < 0.05). Furthermore, the IFN-gamma/IL-4 ratio in the AD group was less than half that of the control group (1.46 +/- 0.2 versus 3.2 +/- 0.1; p = 0.02). Using polymerase chain reaction (PCR), viral genome for rhinovirus (RV) was detected in lung tissue from three of the seven cases in the AD group. Two of these cases also had detectable respiratory syncytial virus (RSV). Viral genome for RSV was detected in five of the AUC group and in one of these cases, RV was also detected. No viral genome was detected in the lungs of the control group. In conclusion, this study provides novel evidence of an aberrant CD8(+) T-cell population, possibly in response to viral infection in subjects who die of acute asthma.

Modulation by gamma interferon of antiviral cell-mediated immune responses in vivo

Mice were infected with lymphocytic choriomeningitis virus and injected once 24 h later with a monoclonal antibody directed against gamma interferon. In comparison with controls, the increase of numbers of CD8+ T cells and the generation of virus-specific cytotoxic T lymphocytes in spleens and virus clearance from organs were diminished, as was the ability of spleen cells to transmit adoptive immunity to infected recipients. The same treatment slightly but consistently lessened rather than augmented the virus titers early in infection, which was also observed in thymusless nu/nu mice. Injection into infected mice of the lymphokine itself in quantities probably higher than are produced endogenously resulted in lower virus titers in spleens but higher titers in livers. The adoptive immunity in infected mice achieved by infusion of immune spleen cells was not altered by treating the recipients with gamma interferon monoclonal antibody. Such treatment did not measurably affect the production of antiviral serum antibodies. We conclude that in lymphocytic choriomeningitis virus-infected mice, gamma interferon is needed for the generation of antivirally active CD8+ T lymphocytes, and furthermore that in this experimental model, direct antiviral effects of the lymphokine elude detection.