动物模型,慢性肠道炎症 z-bo 2020-12-02 471

　　Inflammation animal model: The intestine is a highly complex organ that requires complex animal models to study its function and disease. The different cell populations in the intestine contribute to this complexity. In addition, the intestine contains digested food components and aerobic, anaerobic and facultative anaerobes that keep the environment rich. These bacteria usually have a significant impact on the intestine, and physiological and immune functions. It is necessary to determine the mechanism of intestinal damage, and to prevent disease by developing mitigation strategies. Research using infected human tissue samples provides the most reliable data; however, there are indeed difficulties in obtaining human tissue research, including: the ethics of the use of human tissues. Usually small samples, obvious genetic variation between different individuals. Various mammalian models have been used to study acute and chronic intestinal inflammation. Mice are considered a good animal model because their gut development is relatively similar to that of humans, and they have many of the same immune responses and genes. The rat model has a greater advantage than the mouse and can acquire larger samples for analysis. Invertebrates, including nematodes and fruit flies, have also been used in intestinal research, mainly to investigate mechanisms related to innate immune mechanisms. Zebrafish is widely used to study innate immunity and adaptive immune response. Pigs are commonly used monogastric mammal models because their intestinal function and morphology are similar to humans. Non-human primates (NHPs) provide the best and most comparable data to humans due to the high genetic and physiological similarity of their intestines. The use of non-human primates (NHP) has considerable disadvantages, namely the high cost of research, ethical considerations, and potential dangers, carrying highly pathogenic zoonotic diseases. Other mammals have also been used to investigate intestinal inflammation, including rabbits and guinea pigs. Dogs develop IBD and show gene functions similar to those of human CD patients. Many studies have used animal models to identify IBD biomarkers of inflammatory bowel disease. In general, the above models can be used to determine the mechanism of the occurrence and development of intestinal diseases. In addition, relatively complex surgical models, such as enteric circulation techniques, have been developed to further clarify the mechanism. Although no single animal model is perfect, for studying all the components of intestinal inflammation, each has a unique function to explore various aspects of intestinal injury and disease.

　　Mice: Mice are the most commonly used animal model for intestinal research. Genetically engineered mice are particularly important in studying intestinal inflammation. IL-10 knockout mice C3H and BALB/c are known to be more prone to spontaneous colitis than wild-type C57BL/6 mice. In addition, C57BL/6 mice are more likely to induce Th2 cell-mediated colitis than BALB/c and C3H/HeJ mice. C57BL/6 mice with TCRα chain defects are more likely to induce colitis than BALB/c and C3H/HeJ mice. In addition, it is known that the chemical reagents used to induce chronic intestinal inflammation can be affected by the genetic background of mice. For example, trinitrobenzene sulfonic acid (TNBS) and chemical reagents are used to stimulate CD-like symptoms in mice, which largely depend on genetic background; SJL/J, C3HeJ and BALB/c mice can be modeled with TNBS. CD intestinal lesions in mice, while C57BL/6 mice remained relatively unaffected under the same conditions. Similarly, Swiss Webster and C3H/HeJ dextran sodium sulfate (DSS) mice developed UC-like lesions after administration, but C57BL/6 mice showed less tissue damage after DSS treatment. Most genetically engineered rodent models have been developed, which are only used for research purposes and many gene knockout models are designed to regulate the loss of gene function or overstimulation of pro-inflammatory effector molecules. Immunodeficiency is very effective in clinical research on immune response induced by colitis. The immunocompromised mouse models include severe combined immunodeficiency (SCID) and mice combined with CD4 + CD45RBhigh. Naive T cells lack the ability to produce functional B lymphocytes and T lymphocytes. In these models, supplemented naive T cells interact with antigens and activate them to become T cells, leading to chronic transmural inflammation of the small and large intestines. Other qualities such as the similarity between the mouse and human microbiome, immune response, and the anatomical structure of the monogastric are important considerations when selecting mice to study intestinal injury. Mice share many gut-specific genes with humans. Comparative studies on mouse genomes and genomics have shown that 90% of human and mouse genes are shared, and about 80% of mouse genes are homologous to human genes. In addition, human and mouse intestinal communities show the same species diversity in Firmicutes, Bacteroides, and Proteobacteria. The gastrointestinal tract of mice is also anatomically and functionally similar to humans. More importantly, mice and humans have many similar adaptive immune response functions, such as B cells, T cells, and antibodies. There are some obvious shortcomings in studying human intestinal inflammation in mice and other rodent models. Importantly, people with IBD intestinal lesions are different from mice with intestinal damage observed when exposed to chemicals. For example, although the government's decision supports DSS mice to induce chemical damage to the intestinal epithelium to mimic mucosal damage. But the severity of the disease is different from that of humans. In addition, there are also differences in the expression of TLR2, TLR3, TLR4 and TLR9 between mouse and human. When these cells are exposed to bacterial LPS, the mouse model shows a strong macrophage Toll-like receptor mRNA gene expression pattern.

　　Rat: The rat is also often used as an animal model to study intestinal injury and disease. Many chemicals used to stimulate acute inflammation in mouse models are also useful in rat models. Interestingly, as an example, the TNBS model originally started with rats, which are currently widely used other organisms, such as mice and zebrafish. In addition, other chemical stimuli such as DSS can also induce colonic damage similar to the tissue damage observed in mice. One of the most commonly used transgenic rat models is the HLA-B27 colitis transgenic model, which spontaneously develops gastrointestinal inflammation including gastroduodenitis and colitis, as well as arthritis and spondylitis. Finally, another rat model of acute inflammation was also established by using the biostimulant Campylobacter jejuni, indicating that the animal model of rat colitis induced by chemical and biological agents is useful. Rats are often used in nutrition research. For example, researchers used a rat model to study the effect of a diet rich in fiber on the structure of the gut microbial community. For the changes in community structure observed in the rat feeding experiment, it is important that their observations are similar to those of pigs. This shows that the study of enteral nutrition in rats can be compared with other non-rodent monogastric animal models. Although rats and mice are thought to mainly ferment through the cecum, recent studies have shown that a significant amount of fermentation occurs in the rat colon. Therefore, rats can be used as a model to examine changes in the colon associated with intestinal inflammation or tumors. It has been shown that mutations in the APC gene spontaneously cause tumor development in the intestines of rodents. Interestingly, mutations in the APC gene in rats can cause local tumor development in the colon and rectum. Unlike mice, tumor development is generally limited to the small intestine. Therefore, the murine model of APC gene mutation will be a better choice for studying the pathophysiology of human colorectal cancer than the mouse model. Compared with mice, another advantage of rats is their relatively large body size and larger intestines. For example, the larger size of rats allows better experiments with the chemical stimulus TNBS, and rectal administration of TNBS induces more obvious intestinal damage. Compared to mice, this procedure is easier to perform in larger rat models. The larger intestines of rats can also collect more tissue and allow more data to be collected. Zebrafish: Zebrafish (Danio rerio) has been used as a human intestinal model for many years. Although this is a non-mammalian vertebrate model, it is a highly flexible model that provides researchers with options to study innate immunity and adaptive immunity reaction. Zebrafish are considered by many to be excellent invertebrate models because they have a larger organ and exhibit pathological changes. Similar to nematodes, they have a transparent embryo and larva, relatively simple feeding requirements, and very high yield. The zebrafish intestine has cell types similar to mammals such as intestinal absorption, endocrine cells and goblet cells, brush borders with microvilli function, and constant shedding to luminal epithelial cells. Zebrafish does not have a defined stomach, so its advantage as a nutritional model is limited because most protein and fat absorption occurs in the lower intestine, rather than in the small intestine. Despite this limitation, the zebrafish model has proven useful for studying the loss of intestinal neurons through mutations in intestinal motility and peristalsis. Most studies on inflammation in zebrafish use chemical irritants such as TNBS and DSS. The zebrafish model has been well established to study host-microbe interactions and immune responses caused by bacteria. The establishment of a sterile zebrafish model has enhanced its ability to be applied to microbial research and researchers have used sterile fish to understand and compare the abundance of microbial communities. It takes about 3 weeks for the adaptive immune response of zebrafish to develop and mature. Using zebrafish within 3 weeks of age or younger allows researchers to study the innate immune response without interference from the adaptive immune response. Zebrafish have the functions of innate immunity and adaptive immune response, and their combination with larger animal models can clarify the role of intestinal flora in intestinal diseases. The application of the zebrafish model is very useful for further understanding the effects of acute and chronic inflammation on intestinal cells. It is expected that the model will be used more and more once more biomolecular technologies are developed. The zebrafish's intestine has the additional advantage that it has structural homology with the human intestinal structure. The use of direct real-time imaging technology to observe epithelial cells during infection in real time has significantly increased the effectiveness of this model.

　　Pig: The pig is an excellent mammalian model for studying the mechanisms involved in acute and chronic intestinal injury and inflammation, because the anatomical structure and function of the small intestine are similar to the human intestine. The anatomical structure of the porcine gastrointestinal tract, especially the stomach and small intestine, is similar to the structure of the human gastrointestinal tract, except that only the spiral direction of the porcine colon and the lack of appendix. Nevertheless, the main intestinal functions, such as nutrient and water absorption and microbial fermentation, are still comparable to human intestines. In addition, pig intestinal digestive enzymes, secreted proteins and microorganisms are similar to humans, which facilitates the examination of the relationship between microbial community, diet and intestinal health. The pig model is also widely used to replicate the human microbiome in the pig’s intestine through a fecal transplant procedure. Some studies have also examined the pre-implantation of piglets with probiotic strains commonly found in the human microbiome, and concluded that these strains have a protective effect on subsequent infections by pathogens. Many immune cells, innate immune and adaptive immune system processes, that is, the recognition of activators by human mucosal and intestinal epithelial B and T lymphocytes and innate immune (ie lipopolysaccharide and nucleic acid) phagocytic cells are also the same as human intestinal Immunity is similar. Non-human primates: Non-human primates (NHPs) are considered to be the best animal models to study the mechanisms involved in acute and chronic inflammation, and have irrefutable similarities to human intestinal physiological functions, immunity and intestinal tract microorganism. Monkeys and marmosets are the most common animals used to study the pathogenesis of intestinal diseases and treat them. Monkeys often induce spontaneous colitis and colon cancer after prolonged confinement. For example, Gozalo et al. showed that marmosets develop terminal spontaneous ileitis for an average of 100 months, and initially show chronic diarrhea 3-6 months before diagnosis. Other studies have shown that marmosets can spontaneously develop chronic colitis around 2 years old. Studies have shown that the depression of marmosets and the temperature of the environment in which they are held may contribute to the development of colitis. Although many of the cellular mechanisms involved in the development of spontaneous colitis remain unclear. Ramesh et al. studied the production of cytokines in the gut-associated lymphoid tissue (GALT) of macaques that exhibited persistent diarrhea. Enterocolitis marmosets have higher levels of TNF-α and IL-1α in the intestinal and non-intestinal lymphatic tissues, which are consistent with necrotizing enterocolitis in human patients. Non-human primates have also been used to study the influence of microorganisms on the development of intestinal inflammation, and it has been proven that intestinal bacteria can affect the pathogenesis of diseases. Importantly, the microbiomes of non-human primates, zebrafish and humans all have one thing in common, and imbalances can lead to intestinal diseases. Not only the population of the bacterial community can maintain the intestinal homeostasis, but the intestinal archaea species also help maintain a good microbiome. Investigations have found that the species of methanogenic archaea and sulfate-reducing bacteria (SRB) collectively produce metabolic by-products that affect health and function. In addition, the severity of the disease increases by a large amount of SRB. As the number of these bacteria increases, the concentration of hydrogen sulfide in the colon also increases. It suggests the relationship between methanogenic archaea and SRB and intestinal health. In addition, the genus Rhesus has been used to detect the pathophysiological mechanism of Campylobacter jejuni infection. The results showed that neutrophils and lymphocytes infiltrate the mucosa, accompanied by bloody stools and watery diarrhea. Observe tissue changes caused by acute colitis caused by human Campylobacter. Finally, the macaque population also showed that Helicobacter pylori infection caused specific colitis. Shigella infection in macaques is associated with mucosal invasion, marked by a significant imbalance of electrolyte transport, similar to human bacillary dysentery. The environment of the intestine is in a constantly changing state, in an immune static or activated state. It is already clear that changes in these states can affect the brain function and the body's mental health. Therefore, researchers are now using animal models to study the impact of the gut on mental health. Non-human primates can be used to study the relationship between intestinal flora, the enteric nervous system, and the impact on host health. The gut-brain axis is the functional connection between the intestine and the autonomic nervous system, and is the advanced function of the brain. The innervation of the autonomic nervous system indicates that the intestinal flora affects brain function and behavior, leading to changes in feeding behavior, anxiety-like behavior, stress, depression, and pain. Patients suffering from IBD and IBS can observe many functional changes. Although mice have also been used to study certain aspects of the brain-gut axis, NHPs may be the best model for studying human nervous system activity. Many NHPs are typically able to develop deeper social relationships and display higher levels of human intelligence behavior, making them more suitable for investigating brain-related animal models than mice and pigs. The use of NHPs seems to be the most representative animal model to simulate human intestinal inflammation. However, this model has considerable disadvantages. Most notably, the ethics of the use of highly intelligent animals that are closely related to humans are controversial, resulting in sharp discussions between scientific groups involved in animal research and the public. Many people also believe that NHPs such as the endangered African great ape species should be banned for scientific research. NHPs also need to have specialized, expensive and safe basic animal house facilities, as well as complex equipment that enriches the environment. In addition, several species of NHPs are relatively large (gorillas, chimpanzees and orangutans) and potentially tricky and dangerous animals, requiring trained animal care personnel and veterinarians for feeding and disease control. In addition, NHPs may carry zoonotic pathogens, are highly pathogenic and easily transferred to humans. The most famous and potentially deadly pathogen is the monkey B virus. Although it is relatively harmless to monkeys, exposure to viral secretions can cause

　　Human fatal viral encephalomyelitis.

　　Thinking about ethics, biosafety, and biosafety: The use of animals is allowed, and only when research promises to help understand basic biological principles, or the development of knowledge, can reasonably be expected and benefit human or non-human animals. Only when non-animal substitutes do not exist, select experimental animals. In the study of inflammation, the research must involve the use of animal models (i.e. mimic the complex interactions of host pathogenic microorganisms). Animals used in inflammation models must provide a way to maintain their physical comfort and mental health and must demonstrate the potential value of research animals before research. The hallmark of inflammation is pain, so pain or pain is accompanied by inflammation studies. The extent of the intrusion and implementation procedures must be specified and evaluated in advance. Investigational learning inflammation usually belongs to the internally aggressive category C (ie, mild pressure or short duration of pain) and D (ie, moderate to severe pain or discomfort). However, in rare cases, the study may fall into the aggressive category E (ie, severe pain close to or above the pain threshold in non-anaesthetized awake animals). Since pain must be minimized in intensity and duration, there is no strong reason why studies classified as invasive E will not be approved. Quantitative pain assessment applications are mandatory. Any animal that is observed to experience extreme relentless pain or discomfort must be humanely terminated. Inflammation usually involves the use of enteritis biostimulants (such as pathogens), and research must also meet all necessary biosafety standards to ensure safety.

　　 Choosing the right animal model: Determining the best animal model to study intestinal inflammation is an important consideration. It requires a thorough understanding of the advantages and disadvantages of each model, because there are many factors to consider. Animal models have intestinal anatomy comparable to humans (monogastric and ruminants). Function and microorganisms are the best models for checking intestinal inflammation; pigs, mice, zebrafish, and humans have many common features. In addition, animal models can be genetically engineered and have a human-like genome. Researchers can investigate specific genes related to intestinal diseases. Most certainly, genetically modified mice have become a tool for inflammation research due to their ability to manipulate the phenotypic characteristics of specific genes. The availability of biotechnology and analytical tools is a necessary factor for studying intestinal function and inflammation, and it is also an important consideration for choosing a suitable animal model.

　　 Similar to selecting the best animal model to investigate specific aspects of intestinal inflammation. The selection of the most effective chemical substances and biological agents to induce intestinal inflammation must also be carefully considered.

　　 Chemical stimulants: In animal models of inflammation, chemicals are often used as a quick, economical and effective strategy to induce intestinal tissue damage. Animal models of colitis use DSS or frequent trinitrobenzene sulfonic acid (TNBS) to cause inflammation. Acetic acid, oxazolone, and azomethane oxide (AOM) are also used, but they are smaller than DSS and TNBS. The effectiveness of chemical agents in inducing tissue damage after application varies, depending on the molecular weight, concentration, manufacturer, and batch of chemical substances. In addition, species, gender, and genetic background of animal models also affect the degree of tissue damage. The method of use also affects the induction and severity of the disease. After some chemical substances are ingested, inflammation can be induced well. It functions best when used directly on the site of infection, such as rectal administration. In addition, the microbes in the intestine interact with chemical stimuli to interfere with their ability to induce tissue damage. In general, chemical irritants induced tissue damage can effectively represent clinical symptoms of intestinal inflammation.

　　 dextran sodium sulfate (DSS): dextran sodium sulfate can be used alone or in combination with other chemicals to induce inflammation. By adjusting the concentration and duration of the use of DSS decision support treatment, the mechanism of acute and chronic inflammation can be studied. For example, chronic inflammation in mice can be achieved by using DSS. Within two months, use DSS for 1 week, rest for 2 weeks, and circulate. In contrast, the oral concentration of 1.5% DSS is about 1 week, causing acute inflammation in the intestine. In general, DSS induces inflammation by breaking the epithelial barrier, exposing the lamina propria to luminal contents and bacterial antigens to cause vascular and mucosal damage. This exposure triggers the activation of inflammatory pathways and leads to increased production of inflammatory cytokines, TNF-α, IL-1β, IL-6, IL-10, IL-12 and IFN-γ. Studies have also shown that after the use of DSS, Increase the expression of integrin-α M (ITGAM), integrin-α X (ITGAX) and IL-17. Long-term use of DSS can increase the expression of IL-4 and IL-5, indicating that DSS-induced colitis is mediated by Th1 and Th2 immune mechanisms. In addition, the factors involved in innate immunity are also affected by DSS.

　　 After using DSS, it can change the expression of MyD88, TLR4 and TLR9, and has a slight impact on the innate immunity, which contributes to epithelial cell damage and subsequent intestinal inflammation. Many factors influence the tendency of DSS to induce inflammation in different animal models. The bacterial population in the colon is a key factor that regulates the severity of the tissue response caused by DSS. It was observed that sterile mice treated with DSS can develop severe colitis with 1% DSS. The ability to induce intestinal inflammation after using DSS is also affected by the genetic background of the animal species. For example, C3H/HeJ mice are sensitive to DSS, while C57BL/6 mice are more tolerant. For example, compared with C57BL/6 mice, C3H/HeJ mice experienced more bloody diarrhea, epithelial ulcers, inflammation, and weight loss after using DSS. In addition to mice, pigs have been used to examine intestinal inflammation caused by DSS. Young et al. observed that the expression of TNF-α, IL-6, IFN-γ, and IL-17A in pigs after using DSS increased, similar to the characteristics of IBD in clinical patients. Other studies in pigs reported increased lymphocyte infiltration in mucosal tissues, mucosal erosion and crypt destruction after the use of DSS. These tissue changes are similar to human intestinal lesions with IBD.

　　 Azomethane Oxide (AOM): The severity of inflammation can be enhanced by applying a combination of an inflammatory chemical stimulus and another chemical inducer of inflammation. Long-term administration of the combination of AOM and DSS induces chronic inflammation of the intestine, which often develops into CRC. It is worth noting that the intestinal pathology induced by AOM and DSS is consistent with the changes in the intestine of UC patients. The combined use of these two chemicals changes the cytokines in mouse tissues and leads to increased expression of IL-4 and IFN-γ, similar to those in UC patients. In addition, the use of DSS and AOM is necessary to strengthen DSS-induced colorectal cancer development. It is occasionally seen in patients with UC. Therefore, the combined use of these two chemicals is ideal to investigate the pathophysiology of intestinal inflammatory diseases and colorectal tumors. Trinitrobenzene sulfonic acid (TNBS): Trinitrobenzene sulfonic acid is mainly used to establish animal models of acute intestinal inflammation, but it can also be used to induce chronic chronic diseases in rodents, pigs, rabbits, mice and non-human primates. Inflammation. TNBS needs to be dissolved in ethanol to become an active chemical, and this TNBS ethanol mixture induces intestinal inflammation to change the host protein through the covalent bonding of hapten and TNBS. This process stimulates immune-mediated inflammation. The TNBS ethanol mixture produces self-antigen-modified haptens that are recognized by the host immune system and cause acute intestinal inflammation. In addition, ethanol also acts as an irritant, causing damage to the epithelial barrier. Ethanol-treated TNBS can produce intestinal lesions, representing human intestinal lesions with IBD. It has also been proved that rectal administration of TNBS dissolved in 40-50% ethanol leads to colon shortening, intestinal bleeding, epithelial necrosis and crypt destruction, and increased Th1 immune response in the colon leads to transmural inflammation.

　　 Trinitrobenzene sulfonic acid can be used as both acute inflammation stimulus and chronic inflammation stimulus. In mice with acute inflammation, primary immune response, accompanied by inflammatory Th1 response, increases the expression of IL-12, IFN-γ and TNF-α. Although the use of TNBS as a chemical stimulant for intestinal inflammation has been established in rodents, pigs, and monkeys. There is evidence that mice are the best model for studying TNBS ethanol-induced colitis. When using TNBS to induce tissue damage to select the most suitable mouse, the genetic background and phenotype of the mouse are important factors to consider. As an example, C57BL/6 and DBA/2 strains are tolerant to TNBS, while SJL/J, C3Hej and BALB/c mice have obvious tissue damage after exposure to TNBS.

　　 Oxazolone: Oxazolone is an alternative chemical agent that can be used to produce hapten protein in the host intestine to cause acute intestinal inflammation. Its use leads to intestinal damage mediated by Th2 immune response. Tissue lesions are similar to those of UC lesions in mice after exposure. Most lesions cause mucosal ulcers, submucosal edema and tissue bleeding. The use of oxazolone in mice caused weight loss, diarrhea, ulcers, and damage to large intestinal epithelial cells. Compared with other chemical agents, the advantage of using oxazolone is to induce tissue damage through changes in tissue structure. In fact, oxazolone produces relatively rapid tissue damage, making mice an ideal candidate for studying UC-like diseases. Similar to the use of TNBS and DSS, the choice of mouse type will affect the effect of oxazolone treatment. As an example, treatment of BALB/C and c57bl/6 mice with the same dose of oxazolone showed increased BALB/C tissue damage. Oxazolone is an effective inducer of acute inflammation, and its effectiveness in inducing chronic inflammation is still uncertain.

　　 Biological stimulants: As a substitute for chemical stimulants, biological stimulants are also used to study common intestinal inflammatory diseases. Biological irritants can be bacteria, viruses, protozoa, or worms, which can cause acute and chronic inflammation. We review the most commonly used biologics to induce intestinal inflammation in animal models.

　　 Bacteria: The host intestine contains a rich flora of 1013-1014 species of bacteria. The species usually include Bacteroides, Firmicutes, Actinomycetes, Spirobacteria, and Proteobacteria. The interaction between the host and intestinal microbes is in a steady state, and changes in bacterial species abundance may cause intestinal inflammation. The investigation found that symbiotic bacteria play an important role in preventing the overgrowth of pathogenic bacteria and maintaining intestinal health, helping to regulate and maintain a static intestinal immune system. An uncontrolled immune response of a symbiotic bacteria can cause intestinal damage. Increased exposure to probiotics can increase abnormal immune responses. Changes in the structure of the gut microbial community can cause diseases. A good characteristic model for acute inflammation studies includes the installation and colonization of bacteria in the cecum and large intestine of mice.

　　 worms: Parasites (such as flukes, tapeworms, roundworms) can cause extensive intestinal inflammation and damage, mainly used to study Th2 cell-mediated intestinal inflammation. Parasites mainly induce Th2 (IL-4, IL-5, IL-13 expression) and regulatory T cell factors (IL-10, TGF-β) to associate with eosinophil-related inflammation tissues. Nematodes (such as roundworms) are the most commonly used worm models to study intestinal diseases, and Trichuris murine is the most commonly used nematode that can cause intestinal inflammation in rodents. The acute immune response induced by the T. muris mouse model is characterized by the loss of the barrier function of the cecum and proximal colon. In mouse models such as C57BL/6 and BALB/c mice, infection leads to the up-regulation of IL-4, IL-5 and IL-13 secretion by Th2 cells, which increases the turnover and penetration of epithelial cells. Interestingly, the parasite mainly produces Th2 immune response in the small intestine of mice.

　　 Protozoa: Toxoplasma gondii has also been used in a mouse model to induce intestinal inflammation. Toxoplasma susceptible mice can produce a powerful Th1 cell-related inflammatory response in the small intestine. This microorganism has three pathogenic bacteria, two of which are pathogenic to humans and can cause a strong Th1 type cytokine response, thereby increasing the expression of IL-12 and IFN-γ.