.xiaojian6666@hotmail.com / 18577185183 Chapter 15: 免疫耐受 Immunological Tolerance Xiao Jian .xiaojian6666@hotmail.com / 18577185183

北京大学医学部：张毓教授 北京大学医学部免疫学系主任，卫生部医学免疫学重点实验室主任，北京免疫学会理事长，教育部长江学者特聘教授，国家杰出青年科学基金获得者，973项目首席科学家。长期从事淋巴细胞发育研究，主要成绩包括Hemokinin 等新的发育调节分子的发现与鉴定，以及CD4单阳性细胞胸腺髓质区发育特点的分析和发育程序的建立。肿瘤免疫是实验室近年来拓展的另一研究方向，内容主要包括肿瘤抗原的分离鉴定，肿瘤微环境免疫抑制特性分析，以及肿瘤疫苗的研发。

Tolerance refers to an antigen induced specific unresponsiveness. Immunological Tolerance 免疫耐受 指机体免疫系统接触某种抗原后，针对该抗原的特异性无应答现象。 耐受原---引起免疫耐受的抗原 自身组织抗原  天然诱导耐受； 非自身抗原(如细菌、病毒、毒素、异种个体组 织抗原等) 免疫原  特异性免疫应答 耐受原  无特异性免疫应答 Tolerance refers to an antigen induced specific unresponsiveness.

一 免疫耐受的形成 （一）天然免疫耐受现象 In 1945,Owen first observed immunologic tolerance to allogenic antigen in fetal period cattle of dizygotic twin

Medawar于1953年，成功复制胚胎期诱导免疫耐受 的动物模型。 （二）人工诱导免疫耐受 Medawar于1953年，成功复制胚胎期诱导免疫耐受 的动物模型。 In 1953，Peter Medwar and colleagues induced immunological tolerance to skin allografts in mice by neonatal injection of allogeneic cells

（三）影响后天免疫耐受的抗原因素 抗原的剂量 高剂量抗原引起的耐受称高带耐受 低剂量抗原引起的耐受称低带耐受 诱导T细胞耐受所需抗原量小、发生快、持续时间久 诱导B细胞耐受所需抗原量大、发生慢、持续时间短

B细胞耐受和T细胞耐受 Induction of tolerance in T cells is easier and requires relatively smaller amounts of tolerogen than tolerance in B cells. Maintenance of immunological tolerance requires persistence of antigen. Tolerance can be broken naturally (as in autoimmune diseases) or artificially (as shown in experimental animals, by x‑irradiation, certain drug treatments and by exposure to cross reactive antigens).

其它抗原因素 Factors which affect response影响方式 Favor immune response应答 Tolerance耐受 Physical form of antigen （抗原物理状态） Route of injection （接种途径） Dose of antigen(剂量) Large, aggregated, complex molecules, properly processed Subcutaneous or intramuscular Optimal dose soluble, aggregate-free, simple small molecules, not processed Oral or, sometimes, intravenous Very large or very small dose 抗原持续存在 / 抗原表位特点 / 抗原变异…… 口服抗原易引起耐受分离现象……

Factors that affect response （四）影响免疫耐受的宿主因素 Factors that affect response Favor immune response Favor tolerance Age of responding animal Differentiation state of cells Fully differentiated; memory T & B cells Older, immuno-logically mature Newborn (mice), immuno-logically immature Relative undifferentiated B cell with only IgM, T cells in the thymic cortex 1. 机体的发育程度: 耐受的诱导在 胚胎期最易，新生期次之，成年最难 2. 动物的种属和 品系: 大鼠和小鼠对诱导免疫耐受较敏感 3. 免疫抑制措施的影响: 全身淋巴组织照射/免疫抑制剂 4. 遗传背景

小结：免疫耐受的特点 It is an antigen-induced, active process Like immunologic memory, it is antigen specific Like immunologic memory, it can exist in B cells, T cells or both Like immunologic memory, its easier to induce and lasts longer in T cells than in B cell Induction of tolerance is very similar to induction of an immune response. Immunologic features of tolerance: Tolerance is different from non-specific immunosuppression, and immunodeficiency. It is an active antigen dependent process in response to the antigen. Like immune response tolerance is specific and like immunological memory, it can exist in T-cell, B cells or both and like immunological memory, tolerance at the T cell level is longer lasting than tolerance at the B cell level.

二 免疫耐受的机制 中枢耐受（central tolerance） 外周耐受（peripheral tolerance） 未成熟淋巴细胞在中枢淋巴器官遇到自身抗原形成的耐受 外周耐受（peripheral tolerance） 成熟淋巴细胞在外周淋巴器官遇到自身抗原或非己抗原形成的耐受 Clonal deletion Thymus: negative selection Bone marrow: IgM+, IgD- B cells encountering self antige Immunological ignorance Clonal anergy Lack of co-stimulatory(B7) molecules Exposure to large amounts of antigen Improper antigen presentation Lack of antigenic stimulus Receptor editing Anti-idiotype antibodies Suppressor T cells

1.中枢耐受 部位：发生于中枢免疫器官 包括：T细胞中枢耐受和B细胞中枢耐受 机制：胸腺和骨髓内的阴性选择 克隆清除学说（clonal deletion） 胚胎期的免疫细胞存在着无数具有不同反应特异性的细胞克隆 某一克隆在胚胎期与相应抗原接触后，即被破坏清除或被抑制成为克隆禁忌 该个体出生后再接触同一抗原产生，即表现为对此抗原的无反应性 Frank Burnet 1900--1990 Nobel Prize 1960

T细胞中枢耐受的建立：阴性选择导致克隆清除 被膜 营养细胞 皮质区 胸腺细胞 凋亡细胞 副皮质 巨噬细胞 树突细胞 皮髓质交界 胸腺小体 自身抗原 髓质 髓质上皮细胞 自身抗原包括各组织细胞普遍存在的自身抗原和特定组织表达的组织特异抗原。对后者发生耐受的可能机制是：AIRE（自身免疫调节因子）是一种转录调控因子，可驱使很多原本仅在外周表达的自身抗原在胸腺髓质上皮细胞（mTEC）异位表达或在mTEC凋亡后由胸腺DC摄取并交叉提呈给胸腺细胞，诱导克隆清除。

B细胞中枢耐受的建立：阴性选择和受体编辑 Clonal deletion: B cells expressing only IgM (no IgD) on their surface when exposed to antigen are eliminated.

2.外周耐受 1) Clonal anergy in T cells 部位：发生于外周免疫器官 自身抗原：组织特异性抗原 机制： 克隆失能 克隆清除 免疫忽视 免疫豁免 调节性T细胞 活化诱导的细胞死亡 1) Clonal anergy in T cells iDC Auto-reactive T cells when exposed to antigenic peptides that do not possess co-stimulatory molecules (B7-1 or B7-2) become anergic to the antigen.

2) Clonal anergy in B cells 原因1：长期暴露于可溶性抗原 B cells when exposed to large amounts of soluble antigen down regulate their surface IgM and become anergic and short lived. These cells also up regulate Fas molecules on their surface. An interaction of these B cells with Fas-ligand bearing cells result in their death via apoptosis.

原因2：缺乏Th2细胞的协助 Auto-reactive B cells that escape deletion may not find the antigen or the specific helper T-cells and hence not be activated and die out.

① ② ③ 3) Clonal deletion 4) Clonal ignorance 自身抗原浓度过高或缺乏第二信号引起 No response No clonal deletion No clonal anergy ① Self-reactive T cell clones Corresponding tissue specific Ags Too low ② Immune privileged site 免疫豁免区 ③ TCR对组织特异性自身抗原亲和力低或自身抗原不能得到APC的有效加工 Clonal ignorance: T cells reactive to self antigen not represented in the thymus will mature and migrate to the periphery, but they may never encounter the appropriate antigen because it is sequestered in inaccessible tissues. Such cells may die out for lack of stimulus.

5) Regulatory T cells, Treg 胸腺 CD4+ 5) Regulatory T cells, Treg Foxp3+Treg Foxp3- Foxp3+Treg Foxp3- TGF-β IL-10 Foxp3+Treg Tr1 TE 外周

6) activation induced cell death, AICD 7) 信号转导障碍？

三 免疫耐受的临床应用 1.建立耐受 1) 口服或静注免疫原、建立全身免疫耐受 口服热休克蛋白，诱导Treg产生 器官移植前，给受体静脉注射供者来源的血细胞

2) 可溶性抗原诱导耐受 自身抗原的拮抗肽诱导耐受 筛选自身抗原的拮抗肽 与MHC结合 被TCR结合但不能启动T细胞活化 类风湿性关节炎 可溶性抗原不易被DC摄取，不易导致淋巴细胞活化

3) 阻断共刺激信号

4) 骨髓和胸腺移植 供体骨髓细胞输注建立供受体嵌合体 诱导免疫耐受 给患者移植胚胎胸腺和骨髓，促进免疫耐受的形成

5) 过继输入Treg 6) 诱导免疫偏离 体外扩增Treg，再回输入受者体内，如用于治疗强直性脊柱炎 诱导免疫应答向Th2偏离，避免免疫损伤

2.打破耐受 一.阻断免疫抑制分子 anti-CTLA-4, anti-PD-1, anti-Tim3 二.激活共刺激信号 B7基因转入肿瘤细胞 三.减少Treg的数量或抑制Treg的功能 四.诱导DC成熟 五. 细胞因子及其抗体 IFN-γ、GM-CSF、抗TGF-β抗体 与建立耐受的机制相背而行

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