Nature. Chen Huan and others revealed the mechanism of action of the intestinal lymphatic tissue birth center in mice under physiological conditions.

As the largest and most complex part of the human immune system, the intestinal mucosal system is challenged by tens of millions of antigens, including pathogens, food proteins and intestinal symbionts, every day. The intestinal mucosal immune system consists of gut associated lymphoid tissue (GALT).among them, the organized lymphoid tissue represented by the Peyer's patches (PPS) is the inductive site of the intestinal mucosal immune system, which is responsible for initiating the immune response in the intestinal mucosa and is not only the first line of defense against intestinal pathogen infection, It also plays an important role in the establishment and maintenance of mucosal homeostasis between host and environment.germinal centers (GC) are short-lived tissue structures formed during immune response to antigen stimulation. They are places for clonal expansion and affinity maturation of B lymphocytes. They produce high affinity antibodies against pathogens.different from most secondary lymphoid organs, panchian node of the small intestine forms a constructive GC due to its persistent stimulation by symbiotic flora in the intestinal tract under the physiological conditions without invasion of external pathogens.how these innate germinal centers work, whether they have B-cell clone proliferation, B-cell receptor specific screening and affinity maturation, are all outstanding issues in the field of intestinal immunity.it has been pointed out in the literature that the intrinsic hair growth centers of Pan's node in mice and humans may be different from those in ordinary hair centers, but they can be used as places for nonspecific amplification and diversification of B cells, as seen in birds and other mammals [1].on May 6, 2020, Frederick W. ALT team from Harvard Medical School / Boston Children's Hospital published BCR selection and affinity matching in Peyer's patch geriatric centers (the first author is Dr. Chen Huan, and Yuxiang Zhang and Adam Yongxin ye are co authors).in this paper, we found that a series of antibodies appeared in many mice, which were called public antibodies It is the first time to reveal the role of B lymphocyte clone proliferation, B cell receptor specific screening and affinity maturation in the innate germinal center of the small intestine.because the complexity of potential antigens in small intestine is much higher than that of germinal center reaction induced by pathogens reported in previous literatures, it is necessary to study the B cell receptor group Library of mouse small intestine Pan's node germinal center, and to be able to analyze the affinity maturation process.building such a technology has become the first highlight of this article.the team led by Dr. Chen Huan developed a high-throughput sequencing technology of B-cell receptor group library called "rep SHM SEQ", which can not only measure the full-length V (d) J sequence of B-cell receptor heavy chain (IGH) and light chain (IGL), so as to analyze the CDR3 (complementary determining region 3) of each B-cell receptor, At the same time, we can also use the non productive rearrangement sequence in B cells to construct the somaclonal high frequency mutation (SHM) spectrum when each variable (V) gene is not screened, so as to find the high-frequency mutation screened by the antigenic by Bayesian model, and realize the analysis of affinity maturation process.using this technique, the researchers compared the B-cell receptor group library and the Na ï ve B cell receptor group Library in the pan's node germinal center of wild-type C57BL / 6 mice, In SPF) mice, a series of specific B cell receptor clones were observed to proliferate in the germinal center of Pan's node of small intestine in several mice.some of the B cell receptor clones were still prevalent in germ free (GF) mice, indicating that they were not related to the symbiotic flora, while the other part was from the antigen stimulation produced by the symbiotic flora.the feces of SPF mice were fed by oral gavage to GF mice, and the researchers re observed that the clonal type of B cell receptor induced by symbiotic bacteria increased significantly in the small intestine of multiple mice.by analyzing the high-frequency mutation spectrum of these B-cell receptor clones, the researchers found several high-frequency mutations, all of which appeared in the complementary determining region and led to amino acid sequence changes.these findings suggest that clonal proliferation of B lymphocytes, specific screening of B cell receptors, and affinity maturation do exist in the innate germinal center of the small bowel's node.in order to explore the target antigens of these intestinal common B cell receptor clones and further explain the role of affinity maturation in the innate germinal center of the small intestine, the researchers cloned and expressed the antibodies encoded by these B cell receptor clones in vitro, and carried out bacterial surface polysaccharide microarray screening (bacterial glycan) The antibody induced by symbiotic bacteria has strong affinity to specific bacterial surface polysaccharide antigen. when the high frequency mutations in these antibodies were reduced to the non mutated sequences, their affinity and specificity for binding to specific bacterial surface polysaccharide antigens were greatly reduced, which directly indicated that affinity maturation played an important role in the innate germinal center of Pan's node in mice. the V (d) J rearrangement mechanism of B cell receptor in mice can produce up to 1011 different B cell receptors [2], while the total number of circulating B cells in each mouse under steady state is 108 [3], which means that not every mouse can produce all possible B cell receptors. under this premise, why are these B cell receptor clones found in the natural hair center of the small intestine of multiple mice? The original B cell receptor group library was used to model the V (d) J rearrangement mechanism. It was found that not every B cell receptor was generated with equal probability. The common intestinal B cell receptor clones identified in this paper were generated at high frequency during the V (d) J rearrangement process, indicating that the V (d) J rearrangement mechanism may have been affected by the antigen environment during the process of V (d) J rearrangement. in conclusion, the clonal type of common B-cell receptor in the innate germinal center of Pan's node in mice is a comprehensive result of internal V (d) J rearrangement mechanism bias and external antigen-specific screening. this study shows that the nature and mechanism of action of the intrinsic germinal center in the small intestine of mice is consistent with that of the common transient germinal center. the common antibody phenomenon found in this paper suggests that some antigens should be screened intensively. the non bacterial antigens may come from food type antigens or self antigens. this study is currently being extended from mice to humans, which may have implications for the mechanism of food allergy, inflammatory bowel disease (IBD) and autoimmune diseases. the sequencing technology of B cell receptor group library constructed in this paper has been successfully used in the development of HIV vaccine, and will soon be applied in the development of covid-19 vaccine. Reboldi, A. & amp; cyster, J. g. Peyer's patches: organizing B-cell responses at the internal frontier. Immune. Rev. 271, 230 – 245 (2016). 2. Janeway, C. J., Travers, P., walport, M. & amp; shlomchik, M. Immunobiology: The Immune System in Health and Disease. Garland Science (2005)3. Osmond, D. G. The turnover of B-cell populations. Immunol. Today 14, 34–37 (1993).