Immunological Tolerance, Autoimmunity and Host Defense

Rearrangement of the antigen-specific lymphocyte receptor genes generates repertoire of T and B cells that can attack any emerging pathogens as well as host tissue itself. This horror autotoxicus has to be removed by mechanisms collectively called self-tolerance. Recent advances in immunological science revealed that there are multiple mechanisms of tolerance both in central and peripheral organs. However, it has become more and more apparent that cellular mechanisms that induce tolerance (inactivation) and activation of lymphocytes are quite similar. Possible mechanisms by which immune system distinguishes self-structure from pathogens will be discussed

Two Distinct Pathways Mediated by PA28 and hsp90 in Major Histocompatibility Complex Class I Antigen Processing

Major histocompatibility complex (MHC) class I ligands are mainly produced by the proteasome. Herein, we show that the processing of antigens is regulated by two distinct pathways, one requiring PA28 and the other hsp90. Both hsp90 and PA28 enhanced the antigen processing of ovalbumin (OVA). Geldanamycin, an inhibitor of hsp90, almost completely suppressed OVA antigen presentation in PA28α−/−/β−/− lipopolysaccharide blasts, but not in wild-type cells, indicating that hsp90 compensates for the loss of PA28 and is essential in the PA28-independent pathway. In contrast, treatment of cells with interferon (IFN)-γ, which induces PA28 expression, abrogated the requirement of hsp90, suggesting that IFN-γ enhances the PA28-dependent pathway, whereas it diminishes hsp90-dependent pathway. Importantly, IFN-γ did not induce MHC class I expressions in PA28-deficient cells, indicating a prominent role for PA28 in IFN-γ–stimulated peptide supply. Thus, these two pathways operate either redundantly or specifically, depending on antigen species and cell type

Production of IFN- by CD4+ T cells in response to malaria antigens is IL-2 dependent

T-cell immune responses are critical for protection of the host and for disease pathogenesis during infection with Plasmodium species. We examined the regulation of CD4+ T-cell cytokine responses during infection with Plasmodium berghei ANKA (PbA). CD4+ T cells from PbA-infected mice produced IFN-γ, IL-4 and IL-10 in response to TCR stimulation at levels higher than those from uninfected mice. This altered cytokine response was dependent on parasitemia. To examine the specificity of the response, mice were adoptively transferred with CD4+ T cells from OT-II TCR transgenic mice and were infected with PbA expressing OVA. Unexpectedly, CD4+ T cells from the OT-II-transferred wild-type PbA-infected mice showed high levels of IFN-γ production after stimulation with OVA and the cells producing IFN-γ were not OT-II but were host CD4+ T cells. Further investigation revealed that host CD4+ T cells produced IFN-γ in response to IL-2 produced by activated OT-II cells. This IFN-γ response was completely inhibited by anti-CD25 mAbs, and this effect was not due to the block of the survival signals provided by IL-2. Furthermore, IFN-γ production by CD4+ T cells in response to PbA antigens was dependent on IL-2. These findings suggest the importance of IL-2 levels during infection with malaria parasites and indicate that CD4+ T cells can produce IFN-γ without TCR engagement via a bystander mechanism in response to IL-2 produced by other activated CD4+ T cells

Modulation of Kv Channel Expression and Function by TCR and Costimulatory Signals during Peripheral CD4+ Lymphocyte Differentiation

Ionic signaling pathways, including voltage-dependent potassium (Kv) channels, are instrumental in antigen-mediated responses of peripheral T cells. However, how Kv channels cooperate with other signaling pathways involved in T cell activation and differentiation is unknown. We report that multiple Kv channels are expressed by naive CD4+ lymphocytes, and that the current amplitude and kinetics are modulated by antigen receptor–mediated stimulation and costimulatory signals. Currents expressed in naive CD4+ lymphocytes are consistent with Kv1.1, Kv1.2, Kv1.3, and Kv1.6. Effector CD4+ cells generated by optimal TCR and costimulation exhibit only Kv1.3 current, but at approximately sixfold higher levels than naive cells. CD4+ lymphocytes anergized through partial stimulation exhibit similar Kv1.1, Kv1.2, and/or Kv1.6 currents, but approximately threefold more Kv1.3 current than naive cells. To determine if Kv channels contribute to the distinct functions of naive, effector, and anergized T cells, we tested their role in immunoregulatory cytokine production. Each Kv channel is required for maximal IL-2 production by naive CD4+ lymphocytes, whereas none appears to play a role in IL-2, IL-4, or IFN-γ production by effector cells. Interestingly, Kv channels in anergized lymphocytes actively suppress IL-4 production, and these functions are consistent with a role in regulating the membrane potential and calcium signaling

Recruitment of distinct immune cell populations to the lung after intratracheal TLR4 signaling activation by two different stimulations

The toll-like receptor 4 (TLR4)-mediated immune response is considered as one of the triggers of acute respiratory distresssyndrome. The agonistic monoclonal antibody UT12 specific for the TLR4/MD2 complex induces immune activation in a mannerdistinct from lipopolysaccharide (LPS). In order to compare the effects of this differential TLR4 signaling activation, we examinedimmune cell recruitment to the lung following intratracheal inoculation with UT12 and LPS in mice. The increase in pulmonaryneutrophils was much higher after LPS treatment compared with UT12 treatment, while CD11bhiCD11＋cells increased to similarlevels following both treatments. These changes were MyD88-dependent and TRIF-independent. These differential effects onimmune cell recruitment to the lung suggest distinct underlying mechanisms in response to TLR4 stimulation. These findingsfurther indicate that TLR signaling can lead to different outcomes depending on the ligand and activation pathway, which mayrelate to the complex pathogenesis of inflammatory lung diseases

Daily Feeding of Fructooligosaccharide or Glucomannan Delays Onset of Senescence in SAMP8 Mice

We hypothesized that daily intake of nondigestible saccharides delays senescence onset through the improvement of intestinal microflora. Here, we raised senescence accelerated mice prone 8 (SAMP8) on the AIN93 diet (CONT), with sucrose being substituted for 5% of fructooligosaccharide (FOS) or 5% of glucomannan (GM), 15 mice per group. Ten SAMR1 were raised as reference of normal aging with control diet. Grading of senescence was conducted using the method developed by Hosokawa, and body weight, dietary intake, and drinking water intake were measured on alternate days. Following 38 weeks of these diets we evaluated learning and memory abilities using a passive avoidance apparatus and investigated effects on the intestinal microflora, measured oxidative stress markers, and inflammatory cytokines. Continuous intake of FOS and GM significantly enhanced learning and memory ability and decelerated senescence development when compared with the CONT group. Bifidobacterium levels were significantly increased in FOS and GM-fed mice. Urinary 8OHdG, 15-isoprostane, serum TNF-α, and IL-6 were also lower in FOS-fed mice, while IL-10 in FOS and GM groups was higher than in CONT group. These findings suggest that daily intake of nondigestible saccharides delays the onset of senescence via improvement of intestinal microflora

マラリア感染と治療を繰り返すことにより制御性のCD19陽性B細胞が生じ実験的脳マラリアの発症が抑制される

In African endemic area, adults are less vulnerable to cerebral malaria than children probably because of acquired partial immunity or semi-immune status. Here, we developed an experimental cerebral malaria (ECM) model for semi-immune mice. C57BL/6 (B6) mice underwent one, two and three cycles of infection and radical treatment (1-cure, 2-cure and 3-cure, respectively) before being finally challenged with 104 Plasmodium berghei ANKA without treatment. Our results showed that 100% of naive (0-cure), 67% of 1-cure, 37% of 2-cure and none of 3-cure mice succumbed to ECM within 10 days post challenge infection. In the protected 3-cure mice, significantly higher levels of plasma IL-10 and lower levels of IFN-γ than the others on day 7 post challenge infection were observed. Major increased lymphocyte subset of IL-10 positive cells in 3-cure mice was CD5(?)CD19(+) B cells. Passive transfer of splenic CD19(+) cells from 3-cure mice protected naive mice from ECM. Additionally, aged 3-cure mice were also protected from ECM 12 and 20 months after the last challenge infection. In conclusion, mice became completely resistant to ECM after three exposures to malaria. CD19(+) B cells are determinants in protective mechanism of semi-immune mice against ECM possibly via modulatory IL-10 for pathogenic IFN-γ production.長崎大学学位論文 学位記番号:博(医歯薬)甲第611号 学位授与年月日:平成25年8月7日Author： Lam Quoc Bao , Nguyen Tien Huy , Mihoko Kikuchi, Tetsuo Yanagi, Masachika Senba, Mohammed Nasir Shuaibu, Kiri Honma, Katsuyuki Yui, Kenji HirayamaCitation: PLoS ONE, 8(5), e64836; 2013Nagasaki University (長崎大学)課程博

Characterization of waves of leukocyte recruitment to the lung allograft and the effect of CTLA4-Ig

MHC-mismatched lung allografts are rapidly rejected by the host immune response. We analyzed cells infiltrating the grafted lung tissue using a collagenase-digestion method. The grafted lung was filled with host-derived leukocytes as early as day 1 post transplantation and the majority of the initial infiltrating cells were granulocytes. This initial influx of granulocytes waned rapidly, followed by a steady increase in lymphocytes, particularly T cells, and then by macrophages. The proportion of CD4+ T cells that express CD25 were increased in the graft the majority of which were activated CD4+ cells. We applied cytotoxic T-lymphocyte-associated antigen 4 (CTLA4)-Ig treatment in combination with donor-specific blood transfusion to the transplantation of lung allograft, which was significantly prolonged by the treatment. To examine the cellular and molecular basis of the inhibition of the graft rejection, we evaluated number and cytokine mRNA expression of the cells infiltrating in the lung allograft using collagenase-digestion method, although we were unable to detect significant effects of the treatment. Taken together, this study demonstrates that single cell suspensions from cellular infiltrates of lung tissue is useful for phenotypical and functional studies on cells infiltrating lung tissue after graft transplantation