A population of CD62Llow NK1.1− CD4+ T cells that resembles NK1.1+ CD4+ T cells

In MHC class II−/− C57BL/6 (II−/−) mouse spleen, a small population of CD4⁺ T cells is present of which NK1.1⁺ CD4⁺ (NK) T cells comprise 40 to 45 %. We report here that many of the NK1.1⁻ CD4⁺ T cells derived from II−/− mice are also NK T cells. They produce large amounts of IL-4 in response to anti-CD3 ligation and do so without any requirement for the presence of IL-4 in the priming culture, a property characteristic of NK T cells. Their IFN-γ production is large and is enhanced by IL-12. In addition, II−/− NK1.1⁻ CD4⁺ T cells produce IL-4 as a result of culture with L cells expressing murine CD1 (L-CD1). We report that CD49b, a component of integrin VLA-2, is expressed on the majority of both NK1.1⁺ and NK1.1⁻ NK T cells. NK1.1⁻ NK T cells also exist in wild-type C57BL/6 mice. Evidence supporting this is that Vβ8 usage by CD62L^low NK1.1⁻ CD4⁺ T cells was ∼ 5 % higher than that by CD62L^high CD4⁺ T cells in wild-type mice in keeping with the estimated proportion of NK1.1⁻ NK T cells in the CD62L^low population. CD62L^low CD4⁺ T cells from β2-m−/− mice, which lack NK T cells, showed no increase in Vβ8 usage. When activated by anti-CD3 or L-CD1, CD62L^low NK1.1⁻ CD4⁺ T cells from conventional but not β2-m−/− and CD1−/− mice produce IL-4 in a manner indistinguishable from II−/− NK1.1⁻ CD4⁺ T cells. NK1.1⁻ NK T cells in normal mouse spleens are approximately as numerous as NK1.1⁺ NK T cells.     

Diversion of CD4+ T cell development from regulatory T helper to effector T helper cells alters the contact hypersensitivity response

Cutaneous sensitization to reactive haptens and subsequent challenge results in a T cell-mediated response, contact hypersensitivity (CHS). Recent results from this laboratory have indicated that hapten sensitization induces two populations of reactive T cells: CD8⁺ T cells producing interferon (IFN)-γ which mediate the response and CD4⁺ T cells producing interleukin (IL)-4 and IL-10 which negatively regulate the magnitude and duration of the response. Since CD4⁺ T cell development to either IFN-γ- (Th1) or IL-4/IL-10- (Th2)-producing cells is dependent upon the cytokine environment during antigen priming, we hypothesized that CD4⁺ T cell induction in a Th1-promoting environment would not only alter the CD4⁺ T cell cytokine-producing phenotype but also the course of the CHS response. Administration of the Th1-promoting cytokine IL-12 during hapten sensitization resulted in a CHS response of greater magnitude following challenge and extended the duration of the response. In hapten-sensitized mice depleted of CD8⁺ T cells, treatment with IL-12 induced effector CD4⁺ T cells. Histological examination of challenged ear tissue from these mice indicated minimal edema and an acute mononuclear cell infiltration more typical of classical delayed-type hypersensitivity than CHS. Hapten-primed CD4⁺ T cells from IL-12 treated, sensitized mice produced IFN-γ, but not IL-4 in response to T cell receptor-mediated stimulation. Use of neutralizing anti-IFN-γ antibody indicated that IL-12 not only directly promoted Th1 development but also indirectly inhibited Th2 development through stimulation of IFN-γ production at the time of hapten sensitization. Overall, these results demonstrate that diversion of CD4⁺ T cell development to Th1 effector cells rather than to Th2 cells alters the efferent nature of CHS and removes a primary regulatory mechanism of the immune response.     

CD122+CD8+ Treg suppress vaccine‐induced antitumor immune responses in lymphodepleted mice

Lymphodeleption prior to adoptive transfer of tumor‐specific T cells greatly improves the clinical efficacy of adoptive T‐cell therapy for patients with advanced melanoma, and increases the therapeutic efficacy of cancer vaccines in animal models. Lymphodepletion reduces competition between lymphocytes, and thus creates “space” for enhanced expansion and survival of tumor‐specific T cells. Within the lymphodepleted host, Ag‐specific T cells still need to compete with other lymphocytes that undergo lymphopenia‐driven proliferation. Herein, we describe the relative capacity of naïve T cells, Treg, and NK cells to undergo lymphopenia‐driven proliferation. We found that the major population that underwent lymphopenia‐driven proliferation was the CD122⁺ memory‐like T‐cell population (CD122⁺CD8⁺ Treg), and these cells competed with Ag‐driven proliferation of melanoma‐specific T cells. Removal of CD122⁺CD8⁺ Treg resulted in a greater expansion of tumor‐specific T cells and tumor infiltration of functional effector/memory T cells. Our results demonstrate the lymphopenia‐driven proliferation of CD122⁺CD8⁺ Treg in reconstituted lymphodepleted mice limited the antitumor efficacy of DC vaccination in conjunction with adoptive transfer of tumor‐specific T cells.     

Generation of antitumor response by IL-2-transduced JAWS II dendritic cells

Antigen-loaded dendritic cells (DCs) are a promising tool for inducing a tumor-specific immune response. It seems probable that co-administration of those cells together with cytokine-transduced DCs can further increase effectiveness of the antitumor vaccine. The local production of IL-2 by genetically modified DCs may result in alteration of the unfavorable tumor environment causing immune response dysfunction.In the presented study murine DCs of an established JAWS II cell line were transduced with a retroviral vector carrying murine IL-2 gene (JAWS II/IL-2). JAWS II/IL-2 cells demonstrated slightly decreased tumor antigen (TAg) uptake capacities. However, this modification resulted in enhanced ability of the cells to migrate in vivo. The multiple injection of vaccines containing JAWS II/IL-2 cells caused MC38 tumor growth delay and prolonged mice survival. The immunological response was manifested as cytotoxic natural killer (NK) and T cell activation and tumor tissue infiltration by CD8⁺ and CD4⁺ cells, accompanied by increased IFN-γ production by spleen cells. These observations suggest that repeated peritumoral administration of IL-2-producing dendritic cells can inhibit tumor growth by intensification of CD8⁺ and CD4⁺ cells’ influx into tumor tissue and further activation of the systemic antitumor response. It can be concluded that IL-2 transduced dendritic cells may be used as a potent adjuvant in antitumor immunotherapy.     

Modification of anti-tumor immunity by tolerogenic dendritic cells

Immunosuppressive functions of glucocorticoids (GC) can be mediated via various mechanisms, including the modulation of dendritic cells (DC). Our study investigates the effects of tolerogenic GC-treated DCs on NK and T cell anti-tumor responses in OT-1/Rag^?/? mice, expressing a transgenic TCR in CD8⁺ T cells. The effects caused by GC-treated DCs were compared to the responses to immunogenic, CpG-activated DCs. The effects of DCs on anti-tumor immune responses were analyzed using the EG7 tumor model, where the tumor cells express the peptide epitope recognized by OT-1 T cells. We observed that immunization with CpG and peptide-treated DCs protected against tumor growth by activation of NK cell response. Also, immunogenic DCs induced the expansion of cytotoxic CD8⁺OT-1 cells, expressing activation markers CD44 and CD69 and producing IFNγ. In contrast, the peptide and GC-treated DCs in OT-1 mice increased the numbers of immature Mac-1⁺CD27^? NK cells as well as Foxp3⁺ and IL-10 secreting CD8⁺OT-1 cells with suppressive properties. We conclude that the generation of tolerogenic DCs is one of many immunosuppressive mechanisms that can be induced by GC. Our study demonstrated that tolerogenic DCs modify anti-tumor immune response by suppressing NK cell activity and stimulating the formation of IL-10-secreting CD8⁺ Tregs.     

Distinct Contributions of CD4+ and CD8+ T Cells to Pathogenesis of Trypanosoma brucei Infection in the Context of Gamma Interferon and Interleukin-10

Although gamma interferon (IFN-γ) and interleukin-10 (IL-10) have been shown to be critically involved in the pathogenesis of African trypanosomiasis, the contributions to this disease of CD4⁺ and CD8⁺ T cells, the major potential producers of the two cytokines, are incompletely understood. Here we show that, in contrast to previous findings, IFN-γ was produced by CD4⁺, but not CD8⁺, T cells in mice infected with Trypanosoma brucei. Without any impairment in the secretion of IFN-γ, infected CD8^−/− mice survived significantly longer than infected wild-type mice, suggesting that CD8⁺ T cells mediated mortality in an IFN-γ-independent manner. The increased survival of infected CD8^−/− mice was significantly reduced in the absence of IL-10 signaling. Interestingly, IL-10 was also secreted mainly by CD4⁺ T cells. Strikingly, depletion of CD4⁺ T cells abrogated the prolonged survival of infected CD8^−/− mice, demonstrating that CD4⁺ T cells mediated protection. Infected wild-type mice and CD8^−/− mice depleted of CD4⁺ T cells had equal survival times, suggesting that the protection mediated by CD4⁺ T cells was counteracted by the detrimental effects of CD8⁺ T cells in infected wild-type mice. Interestingly, CD4⁺ T cells also mediated the mortality of infected mice in the absence of IL-10 signaling, probably via excessive secretion of IFN-γ. Finally, CD4⁺, but not CD8⁺, T cells were critically involved in the synthesis of IgG antibodies during T. brucei infections. Collectively, these results highlight distinct roles of CD4⁺ and CD8⁺ T cells in the context of IFN-γ and IL-10 during T. brucei infections.     

DC therapy induces long‐term NK reactivity to tumors via host DC

We vaccinated mice with DC loaded with or without invariant NKT‐cell ligand α‐galactosylceramide and evaluated long‐term resistance against tumor challenge. When mice had been given either DC or DC/galactosylceramide and were challenged with tumor cells even 6–12 months later, both NK and NKT cells were quickly activated to express CD69 and produce IFN‐γ. The NK cells could resist a challenge with several different tumors in vivo. The activated NK and NKT cells could be depleted with anti‐NK1.1 treatment. In spite of this, the activated cells recovered, indicating that tumor‐responsive NK and NKT cells were being generated continuously as a result of vaccination with DC and were not true memory cells. The NK and NKT antitumor response in DC‐vaccinated mice depended on CD4⁺ T cells, but neither CD8⁺T cells nor CD4⁺CD25⁺ regulatory T cells. However, both vaccine DC and host DC were required for the development of long‐term, tumor reactive innate immunity. These results indicate that DC therapy in mice induces long‐lasting innate NK‐ and NKT‐cell activation through a pathway that requires host DC and CD4⁺ T cells and that the continued generation of active NK cells resists the establishment of metastases in vivo.     

The specific NK cell response in concert with perforin prevents CD8<Superscript>+</Superscript> T cell-mediated immunopathology after mouse cytomegalovirus infection

Natural killer (NK) and CD8⁺ T cells play a crucial role in the control of mouse cytomegalovirus (MCMV) infection. These effector cells exert their functions by releasing antiviral cytokines and by cytolytic mechanisms including perforin activation. In addition to their role in virus control, NK cells play an immunoregulatory role since they shape the CD8⁺ T cell response to MCMV. To investigate the role of perforin-dependent cytolytic mechanism in NK cell modulation of CD8⁺ T cell response during acute MCMV infection, we have used perforin-deficient C57BL/6 mice (Prf1^?/?) and have shown that virus control by CD8⁺ T cells in Prf1^?/? mice is more efficient if NK cells are activated by the engagement of the Ly49H receptor with the m157 MCMV protein. A lack of perforin results in severe liver inflammation after MCMV infection, which is characterized by immunopathological lesions that are more pronounced in Prf1^?/? mice infected with virus unable to activate NK cells. This immunopathology is caused by an abundant infiltration of activated CD8⁺ T cells. The depletion of CD8⁺ T cells has markedly reduced pathohistological lesions in the liver and improved the survival of Prf1^?/? mice in spite of an increased viral load. Altogether, the results of our study suggest that a lack of perforin and absence of the specific activation of NK cells during acute MCMV infection lead to an unleashed CD8⁺ T cell response that is detrimental for the host.     

Low-dose cyclophosphamide combined with IL-2 inhibits tumor growth by decreasing regulatory T cells and increasing CD8+ T cells and natural killer cells in mice

Interleukin-2 (IL-2) benefits some cancer patients by promoting the proliferation of cytotoxic effector T cells, but this process is limited by the expansion of regulatory T cells (Tregs). Low-dose cyclophosphamide (CTX) can inhibit the number and function of Tregs. We treated carcinoma-bearing mice with Vehicle, CTX, IL-2 and CTX + IL-2 to investigate the effects of low-dose CTX combined with IL-2 in antitumor treatment. In comparison to monotherapy, CTX + IL-2 significantly limited tumor growth, via tumor cell proliferation inhibition and increased apoptosis. The infiltration of CD8⁺ T cells in tumor tissues was significantly increased in the CTX + IL-2 group. CTX + IL-2 safely increased CD8⁺ T and natural killer cells in the spleen, lymph nodes and peripheral blood, and CTX attenuated the increase in Tregs induced by IL-2 in the spleen.     

Inhibition of anti-GD3-ganglioside antibody-induced proliferation of human CD8+ T cells by CD16+ natural killer cells

The ganglioside GD3 has been described as a membrane component of human T cells which is involved in T cell growth. In the present study the activating function of GD3 for human CD4⁺ and CD8⁺ T cells was analyzed by five different monoclonal antibodies (mAb) directed against the GD3 molecule. Three mAb U5, Z21 and R24 induced strong proliferation of peripheral blood mononuclear cells and purified CD8⁺ and CD4⁺ T cells of normal donors containing less than 5% CD16⁺ natural killer (NK) cells. In contrast to CD4⁺ T cells, CD8⁺ T cells proliferated only weakly in the presence of 15% CD16⁺ NK cells. The proliferative response of purified CD4⁺ and CD8⁺ T cells (<5% NK cells) correlated with the antibody-dependent induction of integral and soluble interleukin-2 (IL-2) receptors and was reduced to 20% by an anti-IL-2 receptor antibody. Our results show, that the GD3 molecule represents an activation molecule for both CD4⁺ and CD8⁺ T cells and that CD16⁺ NK cells selectively inhibit anti-GD3 antibody-induced proliferation of CD8⁺ T cells.     

Vitamin C treatment of mouse bone marrow-derived dendritic cells enhanced CD8 memory T cell production capacity of these cells in vivo

Vitamin C has been found to stimulate dendritic cells (DCs) to secrete more IL-12 and thereby drive naïve CD4⁺ T cells to differentiate into Th1 cells. In the present study, we evaluated the effect of these vitamin C-treated DCs on CD8⁺ T cell differentiation both in vitro and in vivo. Mouse bone marrow-derived DCs were prepared in the presence of GM-CSF and IL-15. With vitamin C treatment, these DCs, when LPS-stimulated, secreted more IL-12p70 and IL-15 than did untreated DCs. And when co-cultured with T cells, they yielded a higher frequency of IFN-γ⁺ CD8⁺ T cells. Moreover, we found that administering vitamin C-treated and tumor lysate-loaded DCs into mice yielded a higher frequency of CD44^high CD62L^low CD8⁺ effector and effector memory T cells, which showed an increased ex vivo killing effect of the tumor cells. These DCs also elicited enhanced protective effects against inoculated tumor cells, most probably by way of the increased cytotoxic T cells, as was revealed by the decreased growth of the inoculated tumor cells in these mice. This ex vivo vitamin C treatment effect on DCs can be considered as a strategy for boosting DC vaccination potency against tumors.     

Antigen-specific CD8+ T cells inhibit IgE responses and interleukin-4 production by CD4+ T cells

There is a growing body of evidence which suggests that CD8⁺ T cells play an important part in regulating the IgE response to non-replicating antigens. In this study we have systematically investigated their role in the regulation of IgE and of CD4⁺ T cell responses to ovalbumin (OVA) by CD8⁺ T cell depletion in vivo. Following intraperitoneal immunization with alum-precipitated OVA, OVA-specific T cell responses were detected in the spleen and depletion of CD8⁺ T cells in vitro significantly enhanced the proliferative response to OVA. Depletion of CD8⁺ T cells in vivo 7 days after immunization failed to enhance IgE production, while depletion of CD8⁺ T cells on days 12–18 greatly enhanced the IgE response, which rose to 26 μ/ml following a second injection of anti-CD8 on day 35 and remained in excess of 1 μ/ml over 300 days afterwards. Reconstitution on day 21 of rats CD8-depleted on day 12 with purified CD8⁺ T cells from animals immunized on day 12 completely inhib ited the IgE response. This effect was antigen specific; CD8⁺ T cells from OVA-primed animals had little effect on the IgE response of bovine serum albumin immunized rats. In vivo, CD8⁺ T cell depletion decreased interferon (IFN)-γ production but enhanced interleukin (IL)-4 production by OVA-stimulated splenic CD4⁺ T cells. Furthermore, CD8⁺ T cell depletion and addition of anti-IFN-γ antibody enhanced IgE production in vitro in an IL-4-supplemented mixed lymphocyte reaction. These data clearly show that antigen-specific CD8⁺ T cells inhibit IgE in the immune response to non-replicating antigens. The data indicate two possible mechanisms: first, CD8⁺ T cells have direct inhibitory effects on switching to IgE in B cells and second, they inhibit OVA-specific IL-4 production but enhance IFN-γ production by CD4⁺ T cells.     

In susceptible mice,Leishmania major induce very rapid interleukin-4 production by CD4+ T cells which are NK1.1−

Susceptibility of BALB/c mice to infection with Leishmania major is associated with a T helper type 2 (Th2) response. Since interleukin-4 (IL-4) is critically required early for Th2 cell development, the kinetics of IL-4 mRNA expression was compared in susceptible and resistant mice during the first days of infection. In contrast to resistant mice, susceptible mice exhibited a peak of IL-4 mRNA in their spleens 90 min after i.v. injection of parasites and in lymph nodes 16 h after s.c. injection. IL-12 and interferon-γ (IFN-γ) down-regulated this early peak of IL-4 mRNA; the effect of IL-12 was IFN-γ dependent. Treatment of resistant C57BL/6 mice with anti-IFN-γ allowed the expression of this early IL-4 response to L. major. The increased IL-4 mRNA expression occurred in Vβ8, 7, 2^? CD4⁺ cells in BALB/c mice and NK1.1^? CD4⁺ cells in anti-IFN-γ treated C57BL/6 mice. These results show that the NK1.1⁺ CD4⁺ cells, responsible for the rapid burst of IL-4 production after i.v. injection of anti-CD3, do not contribute to the early IL-4 response to L. major.     

Mice depleted of CD8+ T and NK cells are resistant to injury caused by cecal ligation and puncture

We previously showed that beta 2 microglobulin knockout mice depleted of NK cells by treatment with anti-asialoGM1 (beta2MKO/alphaAsGM1 mice) are resistant to sepsis caused by cecal ligation and puncture (CLP). beta2MKO mice possess multiple immunological defects including depletion of CD8+ T cells. This study was designed to determine the contribution of CD8+ T and NK cell deficiency to the resistance of beta2MKO/alphaAsGM1 mice to CLP-induced injury. beta2MKO/alphaAsGM1 mice and CD8 knockout mice treated with anti-asialoGM1 (CD8KO/alphaAsGM1 mice) survived significantly longer than wild-type mice following CLP. Improved long-term survival was also observed in wild-type mice rendered CD8+ T/NK cell-deficient by treatment with both anti-CD8alpha and anti-asialoGM1. Blood gas analysis and body temperature measurements showed that CD8+ T and NK cell-deficient mice have significantly reduced metabolic acidosis and less hypothermia compared to control mice at 18 h after CLP. CD8+ T/NK cell-deficient mice also showed an attenuated proinflammatory response as indicated by decreased expression of mRNAs for IL-1, IL-6 and MIP-2 in spleen and heart. IL-6, KC and MIP-2 levels in blood and peritoneal fluid were also significantly decreased CD8+ T/NK cell-deficient mice compared to controls. CD8+ T/NK cell-deficient mice exhibited decreased bacterial concentrations in blood, but not in peritoneal fluid or lung, compared to wild-type controls. These data show that mice depleted of CD8+ T and NK cells exhibit survival benefit, improved physiologic function and an attenuated proinflammatory response following CLP that is comparable to beta2M/alphaAsGM1 mice.     

B cells expressing IL-10 mRNA modulate memory T cells after DNA-Hsp65 immunization

In DNA vaccines, the gene of interest is cloned into a bacterial plasmid that is engineered to induce protein production for long periods in eukaryotic cells. Previous research has shown that the intramuscular immunization of BALB/c mice with a naked plasmid DNA fragment encoding the Mycobacterium leprae 65-kDa heat-shock protein (pcDNA3-Hsp65) induces protection against M. tuberculosis challenge. A key stage in the protective immune response after immunization is the generation of memory T cells. Previously, we have shown that B cells capture plasmid DNA-Hsp65 and thereby modulate the formation of CD8⁺ memory T cells after M. tuberculosis challenge in mice. Therefore, clarifying how B cells act as part of the protective immune response after DNA immunization is important for the development of more-effective vaccines. The aim of this study was to investigate the mechanisms by which B cells modulate memory T cells after DNA-Hsp65 immunization. C57BL/6 and BKO mice were injected three times, at 15-day intervals, with 100 µg naked pcDNA-Hsp65 per mouse. Thirty days after immunization, the percentages of effector memory T (TEM) cells (CD4⁺ and CD8⁺/CD44^high/CD62L^low) and memory CD8⁺ T cells (CD8⁺/CD44^high/CD62L^low/CD127⁺) were measured with flow cytometry. Interferon γ, interleukin 12 (IL-12), and IL-10 mRNAs were also quantified in whole spleen cells and purified B cells (CD43⁻) with real-time qPCR. Our data suggest that a B-cell subpopulation expressing IL-10 downregulated proinflammatory cytokine expression in the spleen, increasing the survival of CD4⁺ TEM cells and CD8⁺ TEM/CD127⁺ cells.     

IL-15 promotes regulatory T cell function and protects against diabetes development in NK-depleted NOD mice

IL-15, an anti-apoptotic cytokine, has been reported to promote the survival and function of NK cells and T cells, including regulatory T cells (Tregs). Here we examined the effect of repeated injections of IL-15 on the development of diabetes in NOD mice. Injection of recombinant murine IL-15, once a day for 2 weeks, neither inhibited nor accelerated diabetes development in untreated NOD mice. However, treatment with IL-15 significantly reduced the incidence and delayed the onset of diabetes in NOD mice that were depleted of NK cells, while NK cell depletion alone had no protection against the disease development. The protective effect in IL-15-treated, NK cell-depleted NOD mice was associated with an increase in immunosuppressive activity of CD4⁺CD25⁺ Tregs. IL-15 also enhanced Foxp3 expression in CD4⁺CD25⁺ cells in an in vitro culture system, and such an effect of IL-15 was abrogated by IL-15-activated NK cells. Inhibition of IL-15-induced Foxp3 expression by IL-15-activated NK cells likely resulted from their IFN-γ production, as recombinant IFN-γ, or the culture supernatant of IL-15-activated wild-type mouse NK cells but not of IL-15-activated IFN-γ-deficient NK cells, mediated a similar inhibition. IFN-γ also diminished the stimulatory effect of IL-15 on Treg function in vitro. These results indicate that IL-15 has the potential to promote Treg function and protect against diabetes development in NOD mice, but such an activity can be eliminated by simultaneous activation of NK cells in IL-15-treated mice.     

Characterization of NK cells and extrathymic T cells generated in the liver of irradiated mice with a liver shield

We previously reported that c-kit⁺ stem cells which give rise to extrathymic T cells are present in the liver of adult mice. Further characterization of extrathymic T cells in the liver of adult mice is conducted here. When mice with a liver shield were lethally (9.5 Gy) irradiated, all mice survived. All tested organs showed a distribution pattern of hepatic lymphocytes on day 7. The distribution pattern in the liver was characterized by an abundance of NK (CD3^? IL-2Rβ⁺) and extrathymic T cells (CD3^int IL-2Rβ⁺) before and after irradiation. To determine their function, post-irradiation allogeneic bone marrow transplantation (BMT) was performed in mice with or without a liver shield. Allogeneic BM cells were rejected in mice with a liver shield and specific activation of CD8⁺ CD3^int IL-2Rβ⁺ cells was induced. At that time, potent cytotoxicity of liver mononuclear cells (MNC) against allogeneic thymocytes was induced. Both NK1.1⁺ and NK1.1^? subsets of CD3^int cells expanded in these mice. An in vivo elimination experiment of the subsets indicated that the NK1.1⁺ subset of CD3^int cells (i.e. NK T cells) was much more associated with the rejection of allogeneic BM cells. However, even after the elimination of NK T cells, allogeneic BM cells were rejected. In this case, granulocytes expanded in parallel with NK1.1^? subsets. Granulocytes may also be associated with the rejection of allogeneic BM cells. These results suggest that the liver is an important haematopoietic organ even in adult life.     

NK1.1+ CD4+ CD8- thymocytes with specific lymphokine secretion

CD4+8^? or CD4^?8⁺ thymocytes have been regarded as direct progenitors of peripheral T cells. However, recently, we have found a novel NK1.1⁺ subpopulation with skewed T cell antigen receptor (TcR) Vβ family among heat-stable antigen negative (HSA^?) CD4⁺8^? thymocytes. In the present study, we show that these NK1.1⁺ CD4+8^? thymocytes, which represent a different lineage from the major NK1.1^? CD4⁺8^? thymocytes or CD4⁺ lymph node T cells, vigorously secrete interleukin (IL)-4 and interfron (IFN)-γ upon stimulation with immobilized anti-TcR-αβ antibody. On the other hand, neither NK1.1^? CD4+8^?thymocytes nor CD4⁺ lymph node T cells produced substantial amounts of these lymphokines. A similar pattern of lymphokine secretion was observed with the NK1.1⁺ CD4⁺ T cells obtained from bone marrow. The present findings elucidate the recent observations that HSA^? CD4⁺8^? thymocytes secrete a variety of lymphokines including IFN-γ, IL-4, IL-5 and IL-10 before the CD4⁺8^? thymocytes are exported from thymus. Our evidence indicates that NK1.1⁺ CD4⁺8^? thymocytes are totally responsible for the specific lymphokine secretions observed in the HSA- CD4⁺8^? thymocytes.     

Murine lupus in MRL/lpr mice lacking CD4 or CD8 T cells

MRL/lpr mice develop a systemic autoimmune disease similar to systemic lupus erythematosus in humans. The mice show progressive lymphadenopathy due to the accumulation of an unusual population of CD4^?8^?(DN) B220⁺ αβ⁺ T cells. We bred MRL/lpr mice with mice lacking CD4⁺ or CD8⁺ T cells by gene targeting via homologous recombination in embryonal stem cells to determine the roles of these cells in the autoimmune disease. No difference in survival or autoantibody levels was noted between CD8-/- lpr and littermate controls. Interestingly, these CD8-/- lpr mice have a reduced level of B220⁺ DN T cells despite the fact that the degree of lymphadenopathy was unaltered. CD4-/- lpr mice had a diminished autoimmune disease with a reduction in autoantibody production and skin vasculitits, and increased survival compared to littermate controls. However, CD4-/- lpr mice had an enhanced splenomegaly that developed massively by 16–20 weeks of age (5 to 8 greater than lpr control mice) due to the accumulation of DN B220⁺ T cells. In addition, there were no differences in peripheral lymph node enlargement, although the proportion of DN B220⁺ T cells was about twofold higher in the CD4-/- lpr mice. These cells were phenotypically identical to the DN population in control lpr mice, indicating that the accumulating DN T cells can be dissociated from the autoimmune disease in these mice. Collectively, our results reveal that the autoimmune disease is dependent on CD4⁺, but not CD8⁺ T cells, and that many of the B220⁺ DN T cells traverse a CD8 developmental pathway.     

Evidence that CD4+, but not CD8+ T cells are responsible for murine interleukin-2-deficient colitis

Mice deficient in interleukin-2 production (IL-2^null mice) develop colonic inflammation closely resembling ulcerative colitis in humans. Although this disease is marked by substantial infiltration of the colon by CD8⁺ and CD4⁺ T lymphocytes, no function has yet been assigned to these T cell subsets in the development of colitis in the IL-2^null mouse. For the present study, we investigated the involvement of T lymphocytes in the onset of colitis in IL-2^null mice, and examined the possible role played by cytotoxic T cells. Both lamina propria lymphocytes (LPL) and intraepithelial lymphocytes (IEL) of the colon of IL-2^null mice were potently cytotoxic ex vivo in short-term redirected cytotoxic lymphocyte (CTL) assays. In contrast, colonic T cells of wild-type animals showed little or no constitutive cytotoxic T cell activity. Colonic CTL were detectable prior to the appearance of disease in IL-2^null animals and CTL activity was confined to the TcRαβ, rather than to the TcRγδ IEL subset. IL-2^null animals crossed with major histocompatibility complex class I-deficient mice [IL-2^null × β₂ microglobulin (β₂m^null] mice also developed colitis, which appeared even earlier than in most IL-2^null mice. These findings suggest that neither CD8⁺ IEL nor LPL were causal in the onset of colitis in IL-2^null animals. In IL-2^null × β₂m^null mice, an ulcerative colitis-like disease was evident from histological studies and immunohistological staining which showed very large numbers of CD4⁺ lymphocytes within the intestinal mucosa. Significant ex vivo killing by CD4⁺ T cells was observed in IL-2^null × β₂m^null animals, although this required an extended incubation time compared to colonic CD8⁺ T cells. Peripheral as well as colonic CD4⁺ T cells in IL-2^null and IL-2^null × β₂m^null animals, were activated as judged by their cell surface phenotype (CD45RB^lo, L-selectin^lo and CD69⁺). In light of these findings, we propose that infiltrating CD4⁺, but not CD8⁺ T cells are central to the inflammation observed in the intestinal mucosa in IL-2^null colitis.