B cell receptor (BCR) is a key molecule involved in B cell specific recognition and the binding of antigens to produce adaptive humoral immune response. Gene rearrangement and high frequency mutation during B cell differentiation are the main mechanisms of BCR diversification. The enormous diversity and unique molecular structure of BCR determine the diversity and specificity of antigen recognition, shaping complex B cell repertoire with extensive collections of antigen specificities. Therefore, BCR antigen-specific information is vital to understanding the adaptive immune characteristics of different diseases. Our ability to connect BCR repertoire and antigen specificity has been enhanced with the development of B cell related research technologies, such as single cell sorting techniques, high-throughput sequencing (HTS), linking B cell receptor to antigen specificity through sequencing (LIBRA-seq). It could help researchers to better understand humoral immune responses, identify disease pathogenesis, monitor disease progression, design vaccines, and develop therapeutic antibodies and drugs. We summarizes recent studies on antigen-specific BCR of infections, vaccinations, autoimmune diseases and cancer. By analyzing autoantibody sequences of SLE as a case, the identification of autoantigens has become potentially possible due to this characterization.
Receptors, Antigen, B-Cell/metabolism* ; B-Lymphocytes/metabolism* ; Lymphocyte Activation ; High-Throughput Nucleotide Sequencing/methods*

OBJECTIVE： To study the effect mechanism of iridoid glycosides extracted from Scrophularia ningpoensis inhibiting cardiomyocytes apoptosis in myocardial infarction model rats. METHODS： The male Wistar rats were randomly divided into sham operation group， model group and S. ningpoensis iridoid glycosides low-dose， medium-dose and high-dose groups， with 10 rats in each group. Myocardial infarction models were established by ligating the left anterior descending coronary artery of the rats， and sham operation group was only threaded without ligation. After the model was established， each administration group was given S. ningpoensis iridoid glycosides suspension intragastrically at three different doses of 50，100，200 mg/kg （by the amount of total glycosides extract） with 10 mL/time， twice a day， for consecutive 7 days. Sham operation group and model group were given constant volume of normal saline intragastrically with same method. The changes of S-T segment of lead ECG Ⅱ were recorded before， after and during 7 days of administration. Cardiac function of rats was examined. The serum levels of LDH， CK-MB， cTnⅠ， NT-pro BNP and TNF-α were determined by colorimetry， immunosuppression or ELISA. The apoptosis of myocardial cells was observed by TUNEL method. SOD activity and MDA content in cardiac myocytes were detected by colorimetry. The expressions of Bcl-2， Bax， Cyt C， Caspase-8， Caspase-9， Caspase-12， Caspase-3 and Calpain in cardiac myocytes were detected by ELISA， enzymolysis colorimetry or enzymatic fluorescence assay. RESULTS： Compared with sham operation， electrocardiogram S-T segment was significantly elevated and the left ventricular end-diastolic diameter and left ventricular end-systolic diameter were significantly increased in the model group； left ventricular ejection fraction and short axis shortening rate decreased significantly； serum levels of LDH， CK-MB， cTnⅠ， NT-pro BNP and TNF-α were increased significantly； there were a large number of yellow-brown apoptotic cells in myocardial tissue； the activity of SOD in myocardial tissue was significantly decreased while the content of MDA was significantly increased； the protein expression level of Bcl-2 and Bcl-2/Bax were significantly decreased， while the levels of Bax， Cyt C， Caspase-3， Caspase-8， Caspase-9， Caspase-12 and Calpain were significantly increased （P＜0.05 or P＜0.01）. Compared with model group， above indexes and pathological changes of myocardial tissue were improved significantly in administration group； the level of Bcl-2 and Bcl-2/Bax in cardiomyocytes increased significantly， while the levels of Bax， Cyt C， Caspase-3， Caspase-8， Caspase-9， Caspase-12 and Calpain decreased significantly （P＜0.05 or P＜0.01）. CONCLUSIONS： S. ningpoensis iridoid glycosides can inhibit the activation of Caspase-3 by inhibiting three apoptotic pathways related to Caspase-8， Caspase-9 and Caspase-12， and then inhibit the apoptosis of cardiomyocytes.