Autonomic regulation of experimental autoimmune encephalomyelitis in IL-4 knockout mice

The effect of chemical sympathectomy induced with 6-hydroxydopamine (OHDA) on experimental autoimmune encephalomyelitis (EAE) was studied in wild type and IL-4^−/− C57BL/6 (B6) mice. When actively sensitized with myelin oligodendrocyte glycoprotein (MOG)_35–55 peptide, control B6 mice developed a mild form of EAE with full recovery. The sympathectomized mice developed paralysis with higher maximum disease score and did not recover completely, indicating that the sympathetic nervous system (SNS) down-modulates the process of EAE. Unexpectedly, however, sympathectomy resulted in suppression of EAE in IL-4^−/− mice, implying that control of actively induced EAE by the SNS depends on the genetic background of mice. We also induced EAE by passive transfer of MOG_35–55-reactive lymph node cells, and this disease was augmented by sympathectomy in both wild type and knockout animals. Further experiments showed that changes in T cell populations and the activity of antigen presenting cells might be responsible for the altered immune response and clinical course after sympathetic ablation. Our studies indicate that the absence of a single cytokine can severely alter nervous–immune system interactions.     

地塞米松对实验性自身免疫性脑脊髓炎小鼠IL-17表达的影响

目的研究地塞米松对实验性自身免疫性脑脊髓炎(EAE)小鼠脑及脊髓组织中IL-17表达水平及脾组织中Th17细胞比例的影响。方法将33只C57BL/6小鼠随机分为对照组、EAE组和地塞米松组。EAE组及地塞米松组小鼠以MOG35-55进行免疫造模。地塞米松组小鼠自免疫当天至处死,隔日给予地塞米松磷酸钠注射液0.07mg·kg~(-1)腹腔注射。对照组及EAE组给予等量生理盐水。观察小鼠的发病情况及神经功能评分。应用苏木精-伊红染色、免疫组织化学染色、实时定量PCR、流式细胞学方法分别检测小鼠中枢神经系统炎症细胞浸润、IL-17阳性细胞表达、IL-17m RNA水平及脾组织Th17细胞比例。结果地塞米松组与EAE组比较,小鼠发病率及神经功能评分明显降低(P0.05)。与对照组比较,EAE组小鼠脑及脊髓组织中炎性病灶数明显增多(P0.05),IL-17阳性细胞数明显增多(P0.05),脊髓组织中IL-17m RNA水平明显升高(P0.05),脾组织Th17细胞比例明显升高(P0.05);与EAE组相比较,地塞米松组小鼠脑、脊髓及脾组织中上述指标明显降低(P0.05)。结论地塞米松可以降低EAE小鼠发病率,减轻发病时神经功能损伤程度以及脑和脊髓内炎性细胞浸润程度,并使IL-17mRNA、蛋白表达水平及Th17细胞比例下降。其神经保护作用可能是通过抑制IL-17/IL-23轴等免疫调节机制而实现。     

Treatment with anti-interferon-gamma monoclonal antibodies modifies experimental autoimmune encephalomyelitis in interferon-gamma receptor knockout mice.

The role of interferon-gamma (IFN-gamma) in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis (EAE) is still controversial. We have studied the function of IFN-gamma and its receptor in the EAE model using two different IFN-gamma receptor knockout (IFN-gamma R(-/-)) mouse types: C57Bl/6x129Sv, with a disruption of the IFN-gamma receptor cytoplasmic domain, and 129Sv, homozygous for a disrupted IFN-gamma receptor gene. Mice were immunized with peptide 40-55 from rat myelin oligodendrocyte glycoprotein. A subgroup of mice was treated with anti-IFN-gamma monoclonal antibodies (mAb) on day 8 postimmunization. Clinical scoring and both histological and immunohistochemical studies were undertaken for all groups. We hereby show that treatment with anti-IFN-gamma mAb worsened the disease course of 129Sv wild-type mice. However, it decreased the mean daily score in IFN-gamma R(-/-) 129Sv and the incidence of the disease down to 50% in C57Bl/6x129Sv IFN-gamma R(-/-) mice. Moreover, after anti-IFN-gamma mAb treatment, oxidative stress levels, metallothionein I and II antioxidant protein expression, and apoptoticneuronal death were increased in wild-type mice while decreased in IFN-gamma R(-/-) mice. These results suggest a putative alternative mechanism of action of this cytokine that works independent of its receptor.     

Experimental autoimmune encephalomyelitis induction in peptidylarginine deiminase 2 knockout mice

During the development of multiple sclerosis the destruction of the myelin sheath surrounding the neurites is accompanied by citrullination of several central nervous system (CNS) proteins, including myelin basic protein and glial fibrillary acidic protein. In experimental autoimmune encephalomyelitis (EAE), a disease induced in animals by immunization with proteins or peptides from the CNS, the animals develop symptoms similar to multiple sclerosis (MS). The increased levels of citrullinated CNS proteins associated with MS are also observed during the development of EAE. To study the role of CNS protein citrullination in EAE development, we induced EAE with a peptide derived from myelin oligodendrocyte glycoprotein (MOG(35-55)) in mice lacking the peptidylarginine deiminase 2 (PAD2) protein, because this enzyme was the most likely candidate to be involved in catalyzing CNS protein citrullination in the diseased state. Even though the PAD2 knockout mice displayed a dramatic reduction in the amount of citrullination present in the CNS, indicating that PAD2 is indeed responsible for the majority of detectable citrullination observed in EAE, the development of EAE was not impaired by genetic deletion of PAD2, suggesting that PAD2 catalyzed citrullination is not essential to the development of EAE.     

IL-10 fails to abrogate experimental autoimmune encephalomyelitis

Mice adoptively-sensitized to develop chronic relapsing experimental autoimmune encephalomyelitis (EAE), a model for the human demyelinating condition, multiple sclerosis (MS), were given injections of recombinant human IL-10 at various timepoints post-sensitization in an attempt to abrogate disease development. IL-10 is a Th2 immunomodulatory cytokine with known down-regulatory effects upon Th1 responses and macrophages. Contrary to a previous report on EAE and the predicted outcome, after repeated experiments, IL-10 was found to elicit a worsening or no effect upon EAE in the mouse. Animals were studied clinically, histopathologically and immunocytochemically. On no occasion was disease ameliorated by IL-10. Pretreatment with IL-10 of lymph node cells used to transfer EAE had no effect upon disease outcome, indicating that the cells were already committed effectors. Administration of anti-IL-10 monoclonal antibody before onset of signs had no effect when given early post-sensitization and caused marked worsening when given immediately before onset of signs. In the context of this autoimmune demyelinating model, these results suggest that IL-10 alone is insufficient to reverse the effector response and indeed may serve to enhance the cascade of events in EAE. © 1996 Wiley-Liss, Inc.     

Radiometric assessment of experimental autoimmune encephalomyelitis in mice

The cell-mediated inflammatory component of experimental autoimmune encephalomyelitis (EAE) in mice is measured by the radioisotopic technique. Mice are challenged with autologous spinal cord homogenate in Freund's complete adjuvant and at various time intervals after such immunization given [125I]5-iodo-2'-deoxyuridine which is incorporated into the mononuclear cell pool. The degree of cell-mediated inflammation is determined by radiometry of the brain and spinal cord tissues. Increased radiolabelling is detected in the brains 2 days prior to the onset of clinical signs of EAE; increased radioactivity of the spinal cord is concomitant with clinical signs. This technique is useful in staging the extent of EAE and may prove to be a powerful tool in studying cell-mediated reactions in other autoimmune diseases.     

小鼠实验性自身免疫性脑脊髓炎的病理变化

目的用髓鞘少突胶质细胞糖蛋白多肽(MOG35-55)诱发实验性自身免疫性脑脊髓炎(experi-m ental autoimmune encephalomyelitis,EAE)小鼠模型。方法应用MOG35-55抗原加完全弗氏佐剂免疫C57BL/6小鼠,利用光镜、电镜观察小鼠组织学改变。结果光镜下可见小血管周围炎细胞浸润,呈袖套状改变、血管周围明显脱髓鞘及神经元变性,B ieschowsky银染显示大量轴索肿胀和轴索卵形体的形成,电镜下可见髓鞘结构松散、断裂或融合,包括不同程度的髓鞘重建,脊髓病变广泛,程度重于脑部。结论EAE的病理改变为血管周围炎性细胞浸润、白质脱髓鞘及髓鞘重建。     

Bladder dysfunction in mice with experimental autoimmune encephalomyelitis

The vast majority of patients with multiple sclerosis (MS) develop bladder control problems including urgency to urinate, urinary incontinence, frequency of urination, and retention of urine. Over 60% of MS patients show detrusor-sphincter dyssynergia, an abnormality characterized by obstruction of urinary outflow as a result of discoordinated contraction of the urethral sphincter muscle and the bladder detrusor muscle. In the current study we examined bladder function in female SWXJ mice with different defined levels of neurological impairment following induction of experimental autoimmune encephalomyelitis (EAE), an animal model of central nervous system inflammation widely used in MS research. We found that EAE mice develop profound bladder dysfunction characterized by significantly increased micturition frequencies and significantly decreased urine output per micturition. Moreover, we found that the severity of bladder abnormalities in EAE mice was directly related to the severity of clinical EAE and neurologic disability. Our study is the first to show and characterize micturition abnormalities in EAE mice thereby providing a most useful model system for understanding and treating neurogenic bladder.     

Behavioral investigation of mice with experimental autoimmune encephalomyelitis

Multiple sclerosis is a neuroinflammatory disease that results in serious neurological disability. Besides physical impairment, behavioral symptoms are also common in patients with multiple sclerosis. Experimental autoimmune encephalomyelitis (EAE) is considered to be a model of multiple sclerosis and mimics the main features of the disease, such as demyelination and motor impairment. In this work, we aimed to study behavioral parameters in animals with EAE using the MOG(35-55) model in C57BL/6 mice. We analyzed memory and anxiety in animals using the elevated plus maze, the step down inhibitory avoidance task and the memory recognition test. No differences in any tests were found when comparing controls and animals induced with EAE. Therefore, we conclude that behavioral changes in animals with EAE induced with MOG(35-55) are probably subtle or absent.     

Experimental autoimmune encephalomyelitis relapses are reduced in heterozygous golli MBP knockout mice

Increased golli MBP (golli) expression has been observed in the peripheral immune system of mice in the relapsing phase of EAE, raising the possibility that golli MBP expression in the periphery may contribute to relapses. Here we describe the generation of golli MBP-deficient mice and a comparison of the clinical course of EAE between heterozygous (golli(+/-)) and wild-type (golli(+/+)) mice. There was no difference between the two groups in incidence of disease, severity of the first episode of disease, or remission after the first episode. However, there was a significant reduction in relapses in golli(+/-) mice vs. controls, suggesting a role for golli proteins in the relapses in EAE.     

实验性自身免疫性脑脊髓炎小鼠的磁共振研究

目的研究动物模型实验性自身免疫性脑脊髓炎(experimental autoimmune encephalomyelitis,EAE)小 鼠中枢神经系统的MR表现。方法使用PLP139-151免疫接种雌性SJL／J小鼠诱导EAE。分别取复发期和缓解期 的EAE小鼠行脑和脊髓常规MR及Gd—DTPA增强MR扫描,并做组织病理学检查。结果PLP139-151能较好的诱 导出慢性复发-缓解型EAE模型,Gd-DTPA增强MR检查能充分显示血脑屏障的破坏,反映脑和脊髓的病灶,而且 显示的病灶相对信号强度复发期明显高于缓解期,在病灶处均可见炎症细胞浸润,髓鞘脱失,病灶周围或远离病灶 处炎症反应轻微。结论Gd—DTPA增强MR检查能准确反映血脑屏障的破坏,病变累及部位及病变程度,为今后使 用药物干预EAE判断疗效、指导进行较准确的病变部位取材时提供了一种更为客观的手段。     

IL-33 blockade suppresses the development of experimental autoimmune encephalomyelitis in C57BL/6 mice

IL-33 is a recently described member of the IL-1 family that has been reported to have a pathogenic role in several inflammatory diseases. In this study, we evaluated the role of IL-33 in a murine model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). We showed that the expression of IL-33 and its receptor, ST2, was markedly elevated in the spinal cord of mice during myelin oligodendrocyte glycoprotein (MOG)(35-55) peptide-induced EAE. Administration of a blocking anti-IL-33 antibody in mice of EAE during the induction phase significantly inhibited the onset and severity of EAE and reduced MOG(35-55)-induced IFN-γ and IL-17 production. In contrast, treatment with recombinant IL-33 worsened the disease course of EAE in association with increased induction of both IFN-γ and IL-17. Furthermore, anti-IL-33 treatment caused a remarkable decrease in expression of IL-17, IFN-γ, T-bet and RORγt, and an upregulation of IL-10 and TGF-β in the spinal cord of EAE mice. These results demonstrate that endogenous IL-33 plays a pivotal role in the pathogenesis of EAE and indicate that blockade of IL-33 has a significant protective effect against EAE.     

B cells from glatiramer acetate-treated mice suppress experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) thought to be primarily mediated by T cells. However, emerging evidence supports an important role for B cells in the pathogenesis and inhibition of MS. Glatiramer acetate (GA), a Food and Drug Administration-approved drug for the treatment of MS, has a good safety profile. But GA's mechanism of action in MS is still elusive. In this study, we showed that B cells from GA-treated mice increased production of IL-10 and reduced expression of co-stimulatory molecules viz.: CD80 and CD86. B cells from GA-treated mice also diminished proliferation of myelin oligodendrocyte glycoprotein (MOG_35-55) specific T cells. Purified B cells transferred from GA-treated mice suppressed experimental autoimmune encephalomyelitis (EAE) in recipient mice compared with B cells transferred from mice treated with PBS or ovalbumin. The treatment effect of GA in EAE was abrogated in B cell-deficient mice. Transfer of B cells from GA-treated mice inhibited the proliferation of autoreactive T cells as well as the development of Th1 and Th17 cells but promoted IL-10 production in recipient mice. The number of peripheral CD11b⁺ macrophages in recipient mice also decreased after transfer of B cells from GA-treated mice; however, the number of dendritic cells and regulatory T cells remained unaltered. These results suggest that B cells are important to the protective effects of GA in EAE.     

他汀类药物对EAE小鼠RhoA表达的影响

目的探讨他汀类药物能否抑制小鼠实验性自身免疫性脑脊髓炎(EAE)模型RhoA蛋白表达及其对小鼠发病情况的影响。方法随机将雌性C57BL/6小鼠分为EAE组、他汀治疗组和佐剂组3组。EAE组和他汀治疗组用髓鞘少突胶质细胞糖蛋白多肽(MOG_(35-55))免疫小鼠建立EAE模型,佐剂组以生理盐水替代MOG_(35-55)同样方法注射;他汀治疗组自免疫后第3天始按体质量10 nag/(kg·d)予阿托伐他汀灌胃。观察3组小鼠发病情况及病理变化并测定脑组织中RhoA蛋白表达。结果与佐剂组相比,EAE组小鼠脑组织中RhoA蛋白表达明显增多(P0.01)。他汀治疗组脑组织RhoA蛋白表达及临床神经功能评分均较EAE组下降(P0.01)。结论 EAE小鼠RhoA蛋白表达上调。他汀类药物可能通过抑制RhoA蛋白表达治疗EAE。     

Niaspan treatment improves neurological functional recovery in experimental autoimmune encephalomyelitis mice

We investigated the treatment of experimental autoimmune encephalomyelitis (EAE) in mice with Niaspan, an agent used to elevate high-density lipoprotein (HDL). EAE mice were treated with Niaspan starting on the immunization or clinical onset day. Neurological functional recovery was significantly increased in the Niaspan treated mice (100 mg/kgbw) compared to the controls. Inflammatory infiltrates were significantly reduced in the Niaspan treatment group compared to the EAE controls. HDL level, intact myelin area, newly formed oligodendrocytes, regenerating axons, gene and protein levels of sonic hedgehog (Shh)/Gli1 were significantly increased in the Niaspan treated mice compared to EAE controls. These data indicate that Niaspan treatment improved functional recovery after EAE, possibly, via reducing inflammatory infiltrates and demyelination areas, and stimulating oligodendrogenesis and axonal regeneration. Niaspan-mediated activation of Shh/Gli1 pathway may promote functional recovery post-EAE.     

乌司他丁对实验性自身免疫性脑脊髓炎小鼠神经的保护作用

目的 研究乌司他丁(UTI)对实验性自身免疫性脑脊髓炎(EAE)髓鞘再生及脑源性神经营养因子(BDNF)表达的影响.方法 24只C57BIZ6雌性小鼠随机分成UTI组(U组)、对照组(S组)和正常组(N组),每组8只,以髓鞘染色观察腰髓髓鞘脱失情况,采用Western blot技术检测并比较各组脑组织BDNF、髓鞘碱性蛋白(MBP)、2',3'-环核甘酸-3'-磷酸水解酶(CNPase)表达浓度.结果 U组小鼠神经功能评分(第12、13、14、22、23、31、33、34、35天时分别为0、0.25、0.38、0.63、0.63、0.40、0.40、0.40和0.40分)明显低于S组(相同时点分别为0.55、0.88、1.00、1.75、2.25、1.00、1.00、1.00和1.00,U=16.00、15.00、14.50、7.50、0.00、14.0、14.50、12.00和14.50,均P＜0.05).U组小鼠髓鞘脱失程度较S组轻.Western blot结果显示U组脑组织BDNF、MBP、CNP(1.96±0.29、2.67±0.48和1.75±0.20)较S组(0.80±0.15、1.36±0.38和1.06±0.18)表达增高,差异具有统计学意义(LSD法,P＜0.05).结论 UTI对EAE具有神经保护作用,其机制可能是通过促进脑组织BDNF表达,保护少突胶质细胞、神经元及促进髓鞘再生.

Abstract：

Objective To investigate the effect of ulinastatin (UTI) on the expression of brainderived neurotrophic factor ( BDNF ) and remyelination in mice with experimental autoimmune encephalomyelitis ( EAE).Methods Twenty-four C57BL/6 mice were randomly divided into UTI group (U),normal saline treated group (S) and normal control group (N,n = 8,respectively).Demyelinations in the spinal cord were observed by solochrome cyanin staining.The expression of BDNF,myelin basic protein (MBP),and 2',3 '-cyclic nucleotide 3'-phosphodiesterase (CNP) in brain tissue of each group were evaluated by Western blot.Results Average clinical scores in group U at the 12,13,14,22,23,31,33,34 and 35 days were 0,0.25,0.38,0.63,0.63,0.40,0.40,0.40 and 0.40 respectively.They were significantly lower than group S at the same time ( U= 16.00,15.00,14.50,7.50,0.00,14.50,14.50,12.00 and 14.50,all P ＜0.05).Solochrome cyanin staining showed that demyelination of spinal cord in group U was also significantly improved than group S.Expressions of BDNF ( 1.96 ± 0.29),MBP (2.67 ± 0.48 ) and CNP ( 1.75 ± 0.20) in group U were all significantly higher than group S ( There were 0.80 ± 0.15,1.36 ± 0.38 and 1.06 ± 0.18 respectively,all P ＜ 0.05).Conclusions UTI has protective effect on EAE.The possible mechanism is that it could promote remyelination,and protect oligodendrocytes and neurons in EAE model by increasing BDNF expression in brain.     

IL-21 receptor expression determines the temporal phases of experimental autoimmune encephalomyelitis

The IL-21 receptor (IL-21R) consists of a unique subunit and a common gamma chain (gamma(c)) that is shared with other cytokines including IL-2, IL-4, IL-7, and IL-15. The interaction between IL-21 and IL-21R results in significant effects on both innate and adaptive immune responses. In this study we examined the influence of IL-21R deficiency (IL-21R(-/-)) on the development of experimental autoimmune encephalomyelitis (EAE), an animal model of human multiple sclerosis (MS). IL-21R(-/-) mice developed EAE earlier and more severe neurological impairment than control mice, yet those mice could effectively recover from neurological deficits. The impact on EAE initiation by IL-21R deficiency was associated with a defect of CD4(+)CD25(+) T regulatory (Treg) cells and a down-regulated expression of Foxp3. The recovery from IL-21R(-/-) EAE was correlated with an expansion of Treg cells as well as an organ-specific redistribution of NK cells. These results suggest that a temporal influence of IL-21 on the activity of immunoregulatory circuits can be important in the modulation of the course of the autoimmune disease.     

Bone marrow stromal cells reduce axonal loss in experimental autoimmune encephalomyelitis mice

We investigated the ability of human bone marrow stromal cell (hBMSC) treatment to reduce axonal loss in experimental autoimmune encephalomyelitis (EAE) mice. EAE was induced in SJL/J mice by injection with proteolipid protein (PLP). Mice were injected intravenously with hBMSCs or PBS on the day of clinical onset, and neurological function was measured daily (score 0-5) until 45 weeks after onset. Mice were sacrificed at week 1, 10, 20, 34, and 45 after clinical onset. Bielshowsky silver was used to identify axons. Immunohistochemistry was performed to measure the expression of nerve growth factor (NGF) and MAB1281, a marker of hBMSCs. hBMSC treatment significantly reduced the mortality, the disease severity, and the number of relapses in EAE mice compared with PBS treatment. Axonal density and NGF(+) cells in the EAE brain were significantly increased in the hBMSC group compared with the PBS group at 1, 10, 20, 34, and 45 weeks. Disease severity was significantly correlated with decreased axonal density and decreased NGF, and increased axonal density was significantly correlated with reduced loss of NGF expression after hBMSC treatment. Most of the NGF(+) cells are brain parenchymal cells. Under 5% of MAB1281(+) cells colocalized with NG2(+), a marker of oligodendrocyte progenitor cells. Nearly 10% of MAB1281(+) cells colocalized with GFAP, a marker of astrocytes, and MAP-2, a marker of neurons. Our findings indicate that hBMSCs improve functional recovery and may provide a potential therapy aimed at axonal protection in EAE mice, in which NGF may play a vital role.     

Time-dependent fate of transplanted neural precursor cells in experimental autoimmune encephalomyelitis mice

Transplanted Neural Precursor Cells (NPCs) are capable of long-distance migration inside the inflamed CNS, but exhibit limited myelinating capacities in animal models of Multiple Sclerosis (MS). Inflammation seems to be both beneficial for the recruitment and migration of NPCs and restrictive for their terminal differentiation. In the present study, a set of transplantation experiments was applied in order to investigate the migratory potential, the differentiation pattern and long-term survival of NPCs in Experimental Autoimmune Encephalomyelitis (EAE) mice, the animal model of MS. The in vitro differentiation potential of NPCs in the presence of either pro- (TNFa, INFγ) or anti- (TGFb) inflammatory cytokines was also analyzed. According to the in vivo results obtained, at the acute phase of EAE only a small fraction of transplanted NPCs succeed to differentiate, whereas at chronic phase most of them followed a differentiation process to glial cell lineage along white matter tracts. However, this differentiation was not fully completed, since 8 months after their transplantation a number of NPCs remained as pre-oligodendrocytes. Glial differentiation of NPCs was also found to be inhibited or promoted following their treatment with TNFa or TGFb respectively, in vitro. Our findings suggest that inflammation triggers migration whereas the anti-inflammatory component is a prerequisite for NPCs to follow glial differentiation thereby providing myelinating oligodendrocytes. It is speculated that the fine balance between the pro- and anti-inflammatory determinants in the CNS may be a key factor for transplanted NPCs to exhibit a better therapeutic effect in EAE and MS. This article is part of a Special Issue entitled "Interaction between repair, disease, & inflammation."     

Enriched environment regulates thymocyte development and alleviates experimental autoimmune encephalomyelitis in mice

Environmental and social factors have profound impacts on immune homeostasis. Our work on environmental enrichment (EE) has revealed a novel anti-obesity and anticancer phenotype associated with enhanced activity of CD8⁺ cytotoxic T lymphocytes in secondary lymphoid tissues. Here we investigated how an EE modulated thymus and thymocyte development. EE decreased thymus mass and cellularity, decreased the double positive thymocyte population, increased the proportion of CD8⁺ T cells, reduced the CD4:CD8 ratio, and downregulated CD69 expression in T cells. In a model of multiple sclerosis: experimental autoimmune encephalomyelitis (EAE), EE alleviated symptoms, inhibited spinal cord inflammation through regulation of type 1 T-helper cells mediated by glucocorticoid receptor signaling, and prevented EAE-induced thymic disturbance. Our mechanistic studies demonstrated that hypothalamic BDNF activated a hypothalamic-pituitary-adrenal axis mediating the EE’s thymic effects. Our results indicate that a lifestyle intervention links the nervous, endocrine, and adaptive immune system, allowing the body to adapt to internal and external environments.