Suppressive effects of antigens on the activity of specific activated lymphocytes : A test to define the specificity of activated lymphocytes

Objective：With the regular mixed lymphocytes culture （MLC） to detect the allograft rejection, the reactivity of the activated lymphocytes （primed lymphocytes） of a recipient shows sometimes increase and sometimes decrease against the antigens from the donor, which is inconsistent with the clinical results. In order to establish a convenient method for testing the specificity of the activated lymphocytes in vitro, so as to know the rejection occurred or not by testing the existence of the specific activated lymphocytes against donor＇s HLA antigens in the recipient＇s peripheral blood. Methods： Anti-IL-2 neutralizing monoclonal antibody （anti-IL-2 N-mAb） and immunosuppressors were introduced in this test system in the presence of specific stimulators and activated lymphocytes. Results ： When the activated lymphocytes were chosen from the one-way MLC 4 d to undergo re-stimulation by specific stimulators, the activity of activated lymphocytes in the treatment group was suppressed significantly compared with that in the control group. The result of this test method is consistent with the biopsy in the clinical diagnosis of rejection. Conclusion：h suggests that the activated lymphocytes can be inactivated by specific antigens in certain conditions. This can be a useful tool to define the specificity of the activated lymphocytes.

Mass screening of prostate cancer in a Chinese population:the relationship between pathological features of prostate cancer and serum prostate specific antigen

Aim:To investigate the pathological features of the prostate biopsy through mass screening for prostate cancer in a Chinese cohort and their association with serum prostate specific antigen (PSA).Methods:A total of 12 027 Chinese men in Changchun were screened for prostate cancer by means of the serum total prostate specific antigen (tPSA) test (by Elisa assay).Transrectal ultrasound-guided systematic six-sextant biopsies were performed on those whose serum tPSA value was >4.0 ng/mL and those who had obstructive symptoms (despite their tPSA value) and were subject to subse- quent pathological analysis with the aid of the statistic software SPSS 10.0 (SPSS.Inc.,Chicago.USA).Results:Of the 12 027 cases,158 (including 137 patients whose serum tPSA values were >4.0 ng/mL and 21 patients [serum tPSA <4. 0 ng/mL] who had obstructive symptoms) undertook prostate biopsy.Of the 158 biopsies,41 cases of prostatic carci- noma were found (25.9 %,41/158).The moderately differentiated carcinoma and poorly differentiated carcinoma ac- counted for 61% and 34 %,respectively.A significant linear positive correlation between the serum tPSA and the Gleason scores in the 41 cases of prostatic carcinoma (r=0.312,P<0.01) was established.A significant linear positive correlation between the serum tPSA value of the 41 prostatic carcinoma and the positive counts of carcinoma in sextant biopsies was established (r=0.406,P<0.01),indicating a significant linear relationship between serum tPSA and the size of tumor. Condusion:This study was the first to conduct mass screening for prostate cancer by testing for serum tPSA values and the first to investigate the pathological features of prostate cancer in a cohort of Chinese men.Our results reveal that the moderately differentiated carcinoma is the most common type of prostate cancer.This study also has shown that the serum tPSA value in prostate cancer is associated with the Gleason score and the size of tumor.

Analysis of Protoscoleces-specific Antigens from Echinococcus Granulosus with Proteomics Combined with Western Blot

Objective To establish and optimize the proteomic analysis of protoscoleces-specific antigens from Echinococcus granulosus. To provide a foundation for identifying specific antigens in the soluble proteins of E. granulosus protoscoleces for further research. Methods Brood capsules were collected aseptically from fertile E. granulosus cysts from the livers of an infected patient. The fertile E. granulosus cysts were fractured, and protoscoleces were collected by centrifugation. The soluble proteins of protoscoleces were acquired using the 2D Quant kit according to the manufacturer＇s instructions. We employed two-dimensional electrophoresis （2-DE） combined with immunoblot assay （Western blot） to analyze the soluble components of E. granulosus protoscoleces antigens. The 2-DE and immunoblot maps obtained were analyzed with PDQuest 8.0 image analysis software. Results About 233 soluble protein spots were identified with Coomassie-stained gels. Most of the proteins had a molecular weight of 16 000 Da to 117 000 Da, and an isoelectric point value of 3.0 to 10.0. 2-DE immunoblot was conducted and 57 specific antigen spots were observed, among which 23 spots were identified. Conclusion 2-DE combined with Western blot is the key to successful proteomic analysis and presents a new possibility for searching the specific E. granulosus protoscoleces antigens.

INTRATHYMIC INOCULATION OF LIVER SPECIFIC ANTIGEN ALLEVIATES LIVER TRANSPLANT REJECTION

Objective To study the effects of liver specific antigen(LSA)on liver allotransplantation rejection. Methods Orthotopic liver transplantation was performed in this study. GroupⅠ: syngeneic control(Wistar-to-Wistar); GroupⅡ: acute rejection(SD-to-Wistar). GroupIII: thymic inoculation of SD rat LSA day 7 before transplantation. The observation of general condition and survival time, rejection grades and the NF-кB activity of splenocytes were used to analyze severity of acute rejection and immune state of animals in different groups. Results The general condition of groupⅠwas fair post transplantation with no sign of rejection. All recipients of group Ⅱ died within days 9 to 13 post transplantation with median survival time of 10.7 ±1.37 days. As for group III, 5 out of 6 recipients survived for a long period with remarkably better ge-neral condition than that of group Ⅱ. Its rejection grades were significantly lower than groupⅡ(P < 0.05).NF-кB activity was only detected in groupⅠbetween days 5 and 7 after transplantation, whereas highactivity of NF-кB was detected at all points in group Ⅱ and low NF-кB activity was detected in group III which was significantly lower than that of group Ⅱ(P < 0.05). Conclusions LSA is an important transplantation antigen directly involved in the immunorejection of liver transplantation. Intrathymic inoculation of LSA can alleviate the rejection of liver allotransplantation,grafts survive for a period of time thereby, allowing a novel way to liver transplantation immunotolerance.

Intrathymic inoculation of donor liver specific antigen alleviates rejection of liver allotransplantation

Use and effects of liver specific antigen in orthotopic liver transplantations were researched in this study. Group I:syngeneic control (Wistar to Wistar); Group II:acute rejection (SD to Wistar ); Group III: Thymic inoculation of SD rat LSA day 7 before transplantation. The observation of common situation and survival time, rejection grades, NF κB activity of splenocytes and IL 2mRNA expression of grafted liver were used to analyze acute rejection severity and immune state of animals in different groups. The common situation of group I was very well after transplantation and no signs of rejection were found. Recipients of group II lost body weight progressively. All dead within day 9 to day 13 posttransplantation; median survival time was 10.7 ±0.51 days. It was an optimal acute rejection control. As for group III, 5 out of 6 recipients survived for a long time and common situation was remarkably better than that of group II. Its rejection grades were significantly lower than that of group II( P <0.05). NF κB activity was only detected in group I at day 5 and day 7 after transplantation, whereas high activity of NF κB was detected at all time points in groupII and the low NF κB activity detected in group III was significantly lower than that of group II ( P <0.05). No IL 2mRNA expression was detected at any time point in group I,whereas high level expression was detected at all time points in group II and the low level expression only detected at day 3 in group III was significantly lower than that of group II ( P <0.05). Conclusion: LSA is an important transplantation antigen which is involved directly in the immunorejection of liver transplantation. We report here for the first time that intrathymic inoculation of LSA can alleviate the rejection of liver allotransplantation; and that grafts can survive for a long time thereby, thus leading to a novel way to achieve liver transplantation immunotolerance.

Construction of Smac gene-containing and human prostate specific antigen promoter-regulated vector and its expression

To construct an eukaryotic expression vector containing Smac gene and study the expression efficiency and specificity of prostate specific antigen（PSA） enhancer/promoter in a possible targeted gene therapy scheme for prostate cancer. Methods： PSA enhancer （PSAE） and promoter （PSAP） sequences were amplified using PCR method. CMV and T7 promoters were deleted from pcDNA3.1-Smac and replaced by the two specific fragments to generate pPSAE-PSAP-Smac. After transfection into different cell lines, the status of cells was observed. And then, we determined the relative concentration of Smac mRNA in RT-PCR. Results： The recombinant plasmid of pPSAE-PSAP-Smac was successfully constructed. And only the prostate cancer cell line PC-3 was suppressed after transfection with pPSAE-PSAP-Smac. However, other nonprostate lines were not. Moreover, the concentration of Smac mRNA regulated by PSA promoter and enhancer was higher in comparison to the CMV promoter-driven control vectors. Conclusion： An expression vector containing the Smac gene （based on elements of the PSA gene regulatory sequences） has been developed and shown to function in prostate cancer cell lines which provides a solid platform for launching clinical studies.

In vitro and in vivo analyses of a genetically-restricted antigen specific factor from mixed cell cultures of macrophage, T and B lymphocytes

An immunostimulatory factor was identified to be secreted by antigen-pulsed maorophages. This factor was able to induce the generation of antigen specific T helper lymphocytes in vitro as well as in vivo. Further in vitro experiments testing for the genetic restriction of this factor indicated that it is a genetically-restricted antigen specific factor (ASF). The Cunningham plaque assay was used to quantify the generation of T helper lymphocytes by measuring the number of plaque forming cells after sequential incubations of antigen-pulsed maorophages with T lymphocytes, and then spleen cells, and finally the TNP-coated sheep red blood cells.

Prostate specific antigen bounce after intensity-modulated radiation therapy in an Asian population

Objective:Serum prostate specific antigen(PSA)is commonly used to evaluate treatment response after definitive radiation therapy(RT).However,PSA levels can temporarily rise without a clear reason,termed“PSA bounce”,and often engender great anxiety for both patients and physicians.The present study aimed to determine the prevalence and factors that predict“PSA bounce”after intensity-modulated radiation therapy(IMRT),and the relevance to biochemical failure and cancer recurrence in an Asian population.Methods:We retrospectively reviewed 206 patients who received IMRT for prostate cancer from 2004 to 2012 in the National Cancer Centre Singapore.These patients were followed up with regular PSA monitoring.We defined“PSA bounce”as a rise of 0.1 ng/mL,followed by two consecutive falls.Patients with biochemical failure(PSA nadir t 2 ng/mL)were further evaluated for cancer recurrence.Results:Sixty-one patients(29.6%)experienced“PSA bounce”,at a median time of 16 months and lasted for 12 months.Age remained the most consistent predictor of the incidence,duration and extent of“PSA bounce”.Other contributory factors included baseline PSA,Gleason score and PSA nadir.Hormonal therapy and prostate volume did not affect this phenomenon.Sixteen patients(7.8%)developed biochemical recurrence,at median time of 32 months,of which 11 were confirmed to have metastatic disease.The median follow-up time was 71 months.

Early diagnosis of prostate cancer using free/total prostate specific antigen ratio: a population based screening data

Aim: To evaluate the use of free/total prostate specific antigen ratio (fPSA/tPSA ratio) in improving the early diagnosis of prostate cancer. Methods: The fPSA/tPSA ratio in the serum was analyzed in 187 men with tPSA ranging between 4.0 and 20.0 μg/L. All of them underwent ultrasound guided sextant prostatic biopsy. The results were calculated by SPSS 10.0 software. Results: (1) When the tPSA was within the ranges of 4.0 - 10.0 and 10.0 -20.0 μg/L, the prostate cancer detection rate was 18.1 % and 22.5 %, respectively; (2) The area under the curve (AUC) was bigger in fPSA/tPSA than in tPSA (P<0.05) in all the men; (3) When the cut off value of fPSA/tPSA ratio was set at 0.25 and the tPSA at 4.0 - 10.0 μg/L and 10.0 - 20.0 μg/L, the diagnostic sensitivity of tPSA was 90.5 % and 87.5 %, respectively. Thus at the tPSA ranges of 4.0 - 10.0 and 10.0 - 20.0 μg/L, 26.7 % and 11.3 % of biopsies could be avoided, respectively. Conclusion: The use of fPSA/tPSA ratio can improve the prostate cancer detection rate and reduce unnecessary biopsies when tPSA is within the range of 4.0 - 20.0 μg/L.

Contemporary outcomes in the detection of prostate cancer using transrectal ultrasound-guided 12-core biopsy in Singaporean men with elevated prostate specific antigen and/or abnormal digital rectal examination

Objective:Despite being the third commonest cancer in Singaporean men,there is a dearth of basic data on the detection rate of prostate cancer and post-procedure complication rates locally using systematic 12-core biopsy.Our objective is to evaluate prostate cancer detection rates using 12-core prostate biopsy based on serum prostate specific antigen(PSA)levels and digital rectal examination(DRE)findings in Singaporean men presenting to a single tertiary centre.The secondary objective is to evaluate the complication rates of transrectal prostate biopsies.Methods:We retrospectively examined 804 men who underwent first transrectal-ultrasound(TRUS)guided 12-core prostate biopsies from January 2012 to April 2014.Prostate biopsies were performed on men presenting to a tertiary institution when their PSA levels were
4.0 ng/mL and/or when they had suspicious DRE findings.Results:Overall prostate cancer detection rate was 35.1%.Regardless of DRE findings,patients were divided into four subgroups based on their serum PSA levels:0e3.99 ng/mL,4.00 e9.99 ng/mL,10.00e19.99 ng/mL and
20.00 ng/mL and their detection rates were 9.5%,20.9%,38.4% and 72.3%,respectively.The detection rate of cancer based on suspicious DRE findings alone was 59.2% compared to 36.5% based on serum PSA cut-off of 4.0 ng/mL alone.The post-biopsy admission rate for sepsis was 1.5%.Conclusion:In conclusion,using contemporary 12-core biopsy methods,the local prostate cancer detection rate based on serum PSA and DRE findings has increased over the past decade presumably due to multiple genetic and environmental factors.Post-biopsy sepsis remains an important complication worldwide.

Analysis of results related to the percent free prostate specific antigen among men without prostate diseases in Xi'an area

To measure the percent of free prostate specific antigen （fPSA） among men without prostate diseases in Xi＇an area, and to study the relationship of percent fPSA with age and pathological grade, clinical stage of prostate cancer （PCa） with percent fPSA, and to analyze the difference between the data in China and the.overseas data to determine appropriate reference range for Chinese male. Methods： A total of 713 participants were enrolled into the study, with PSA, fPSA in serum measured and the percent fPSA calculated. Out of 713 cases, 679 without prostate diseases were divided into 5 groups by age, and then the relationships of PSA, fPSA and percent fPSA with age were studied, respectively. The relationship of pathological grade and clinical stage with percent fPSA of the 34 participants with PCa was also studied. With the help of the related data of men without prostate disease, the appropriate reference range for Chinese male was established. Results： The increases in PSA or fPSA were correlated with age, while there was no significant correlation between age and percent fPSA. The percent fPSA was also correlated with pathological grade and clinical stage of PCa. The percent fPSA of men without prostate disease in Xi＇an area was significandy lower than that in the related overseas data. The reference range of percent fPSA for Chinese male was≥ 15%. Conclusion： Percent fPSA might be more useful than PSA in the detection of prostate cancer. As the percent fPSA is decreased, the pathological grade is decreased, and the clinical stage is increased, the malignant degree is increased. The reference range of ≥15% is more appropriate for Chinese male.

Salvage treatments for prostate-specific antigen relapse of cT3N0M0 prostatic adenocarcinoma after radical prostatectomy combined with neoadjuvant androgen deprivation

Objective The aim of the study was to evaluate the efficiency of salvage treatments for prostate specific antigen(PSA)relapse of cT3N0M0 prostatic adenocarcinoma(PCa)after radical prostatectomy(RP)combined with neoadjuvant androgen deprivation(ADT).Methods A total of 332 patients with cT3N0M0 PCa were enrolled in the prospective study and received RP and pelvic lymph node dissection with neoadjuvant ADT for 3 months.All patients with PSA relapse were treated with salvage external beam radiation therapy(RT)and ADT for 6 months.Results The 5-year postoperative PSA relapse rate was 40.96%(136/332).The patients have been divided into the PSA relapse and PSA relapse-free groups in order to compare patient characteristics.The ratio of patients with Gleason score≥8 and positive surgical margin in the PSA relapse group were significantly higher than those of in the PSA relapse-free group(P=0.01).The mean duration between the start of operative treatment and PSA relapse was 31 months.Salvage treatment to all 136 PSA relapse patients led to favorable outcomes.PSA relapse was not observed after salvage treatment by the end of follow-up.The 5-year overall survival rates of the PSA relapse and PSA relapse-free groups were 94.9%and 93.9%,respectively.Conclusion In pursuit of curative treatment,our study showed that RP combined with neoadjuvant ADT is an aggressive multimodality strategy associated with lower PSA relapse and better survival outcomes for stage cT3N0M0 PCa patients.Patients with PSA relapse after RP may benefit from early aggressive salvage RT combined with short-term ADT.

Combined Detection of Serum Heat Shock Protein-90<i>α</i>and Prostate Specific Antigen for Prostate Cancer Diagnosis

Objective: To explore the relationship between heat shock protein-90α (HSP-90α) and occurrence of prostate cancer, and clinical value of combined detection of serum HSP-90α and prostate specific antigen (PSA) in the diagnosis of prostate cancer. Method: A total of 30 patients with prostate cancer, 30 patients with benign prostatic hyperplasia (BPH) and 30 healthy men (control group) were selected from September 2018 to September 2019, then to detect levels of serum HSP-90α, total PSA and free PSA (FPSA) by ELISA, serum testosterone level by radioimmunoassay, prostate cancer tissue was removed by operation, and relative expression of tissue HSP-90α protein by Western blot. Results: The levels of serum HSP-90α and total PSA in prostate cancer group were significantly higher than other two groups, and testosterone level was lower than other two groups (P < 0.05);there was no difference of serum FPSA level between the three groups (P > 0.05). It was found by Pearson test that serum HSP-90α was positively correlated with total PSA level (r = 0.659, P = 0.005), while negatively correlated with testosterone level (r = -0.549, P = 0.006). According to TNM stage of prostate cancer, there were 17 cases of stage I - II, 13 cases of stage III - IV, 6 cases of Gleason score 1 - 4, 13 cases of 5 - 7, 11 cases of 8 - 10, tumor diameter range from 0.8 to 6.2 cm, with average of (3.9 ± 1.5) cm. The relative expression of HSP-90α protein in tumor tissue was closely related to TNM stage, Gleason score and tumor diameter (P < 0.05). By ROC analysis, it was found that accuracy of combined detection of serum HSP-90α and PSA levels for prostate cancer diagnosis was 0.896, and that of single PSA detection was 0.852. Conclusion: Higher expressions of HSP-90α in prostate cancer tissue and serum may be closely related to occurrence and development of prostate cancer, and combined detections of serum HSP-90α and PSA levels are of great significance in improving early diagnosis of prostate cancer.

Anti-tumor effects induced by gene vaccines co-expressing truncated human prostate specific membrane antigen gene and mouse 4-1BBL

Objective To investigate the influence of m4-1BBL on anti-tumor effects induced by truncated human prostate specific membrane antigen ( tPSMA ) gene in mice. Methods A eukaryotic expression plasmid encoding tPSMA and m4-1BBL ( pDC316-tPSMA-IRES m4-1BBL) ,pDC316-tPSMA and pDC316 were constructed.

Inhibitory Effect of Matrine on the Expression of PSA and AR in Prostate Cancer Cell line LNCaP

In order to investigate the inhibitory effect of matrine on the expression of prostate specific antigen （PSA） and androgen receptor （AR） in prostate cancer cell line LNCaP in vitro, LNCaP cells were treated with matrine at different concentrations （0.5, 1.0, 1.5, 2.0 g/L） for 12-36 h. The growth activities of cancer cells were determined by MTT colorimetric assay. The AR level was measured by Western blotting. The expression of PSA was detected by using AXSYM system-chemical luciferase methods. The results showed that matrine could effectively inhibit the growth of androgen-dependent prostate cancer cell line LNCaP in vitro in a time-and dose-dependent manner （P〈0.05）. It could obviously decrease the level of AR （P〈0.01） and inhibit the expression of PSA in a dose-dependent manner （P〈0.05） in LNCaP cells. It was concluded that matrine could significantly suppress the growth of LNCaP cells and inhibit the expression of PSA and AR of prostate cancer cells.

A phase 3,double-blind,randomized placebo-controlled efficacy and safety study of abiraterone acetate in chemotherapynaı¨ve patients with mCRPC in China,Malaysia,Thailand and Russia

Objective:This double-blind,placebo-controlled phase 3 study was designed to compare efficacy and safety of abiraterone acetate+prednisone(abiraterone)to prednisone alone in chemotherapy-naı¨ve,asymptomatic or mildly symptomatic metastatic castrationresistant prostate cancer(mCRPC)patients from China,Malaysia,Thailand and Russia.Methods:Adult chemotherapy-naı¨ve patients with confirmed prostate adenocarcinoma,Eastern Cooperative Oncology Group(ECOG)performance status(PS)grade 0e1,ongoing androgen deprivation(serum testosterone<50 ng/dL)with prostate specific antigen(PSA)or radiographic progression were randomized to receive abiraterone acetate(1000 mg,QD)t prednisone(5 mg,BID)or placebo t prednisone(5 mg,BID),until disease progression,unacceptable toxicity or consent withdrawal.Primary endpoint was improvements in time to PSA progression(TTPP).Results:Totally,313 patients were randomized(abiraterone:n Z 157;prednisone:n Z 156);and baseline characteristics were balanced.At clinical cut-off(median follow-up time:3.9 months),80% patients received treatment(abiraterone:n Z 138,prednisone:n Z 112).Median time to PSA progression was not reached with abiraterone versus 3.8 months for prednisone,attaining 58%reduction in PSA progression risk(HR=0.418;p<0.0001).Abirateronetreated patients had higher confirmed PSA response rate(50%vs.21%;relative odds=2.4;p<0.0001)and were 5 times more likely to achieve radiographic response than prednisonetreated patients(22.9%vs.4.8%,p=0.0369).Median survival was not reached.Most common(≥10% abiraterone vs.prednisone-treated)adverse events:bone pain(7%vs.14%),pain in extremity(6%vs.12%),arthralgia(10%vs.8%),back pain(7%vs.11%),and hypertension(15%vs.14%).Conclusion:Interim analysis confirmed favorable benefit-to-risk ratio of abiraterone in chemotherapy-naı¨ve men with mCRPC,consistent with global study,thus supporting use of abiraterone in this patient population.

Differentiation of lethal and non lethal prostate cancer： PSA and PSA isoforms and kinetics

Prostate-specific antigen （PSA） testing for the early diagnosis of prostate cancer has led to a decrease in cancer mortality. However, the high prevalence of low-grade prostate cancer and its long natural history, competing causes of death in older men and treatment patterns of prostate cancer, have led to dramatic overtreatment of the disease. Improved markers of prostate cancer lethality are needed to reduce the overtreatment of prostate cancer that leads to a reduced quality of life without extending life for a high proportion of men. The PSA level prior to treatment is routinely used in multivariable models to predict prostate cancer aggressiveness. PSA isoforms and PSA kinetics have been associated with more aggressive phenotypes, but are not routinely employed as part of prediction tools prior to treatment. PSA kinetics is a valuable marker of lethality post treatment and routinely used in determininE the need for salva=e theraov.

Prostate chronic inflammation type Ⅳ and prostate cancer risk in patients undergoing first biopsy set:Results of a large cohort study

Objective:In prostate specimens,chronic inflammatory infiltrate(CII)type Ⅳ has been detected,but its association with prostate cancer(PCa)is controversial.The aim of the present study is to investigate on associations of CII with PCa detection in patients undergoing prostate first biopsy set.Methods:Ultrasound transrectal-guided biopsies by the transperineal approach were retrospectively evaluated in 441 consecutive patients.The study excluded patients who were in active surveillance,prostate specific antigen(PSA)
30 ng/mL,re-biopsies,incidental PCa after transurethral resection of the prostate(TURP),less than 14 cores or metastatic.Analysis of population and subpopulations(with or without PCa)was performed by statistical methods which included ManneWhitney(U test),KruskaleWallis test,Chi-squared statistic,logistic regression.Multivariate logistic regression models predicting mean probability of PCa detection were established.Results:PCa detection rate was 46.03%.Age,PSA,prostate volume(PV),prostate intraepithelial neoplasia(PIN)and CII were the significant independent predictors of PCa detection.PV(OR Z 0.934)and CII(OR Z 0.192)were both negative independent predictors.CII was a significant negative independent predictor in multivariate logistic regression models predicting the mean probability of PCa detection by age,PSA and PV.The inverse association of CII with PCa does not necessary mean protection because of PSA confounding.Conclusion:In a population of patients undergoing prostate first biopsy set,CII was a strong negative independent predictor of PCa detection.CII type Ⅳ should be considered as an adjunctive parameter in re-biopsy or active surveillance protocols.

Molecular mechanism of modulating the liquefaction epididymal protease inhibitor of human semen

Aim： To study the molecular mechanism of epididymal protease inhibitor （Eppin） modulating the process of prostate specific antigen （PSA） digesting semenogelin （Sg）. Methods： Human Sg cDNA （nucleotides 82-849） and Eppin cDNA （nucleotides 70-423） were generated by polymerase chain reaction （PCR） and cloned into pET-100D/TOPO. Recombinant Eppin and Sg （rEppin and rSg） were produced by BL21 （DE3）. The association of Eppin with Sg was studied by far-western immunoblot and radioautography. In vitro the digestion of rSg by PSA in the presence or absence of rEppin was studied. The effect of anti-Q20E （N-terminal） and C-terminal of Eppin on Eppin-Sg binding was monitored. Results： Eppin binds Sg on the surface of human spermatozoa with the C-terminal of Eppin （amino acids 75-133）. rSg was digested with PSA and many low molecular weight fragments were produced. When rEppin is bound to rSg, then digested by PSA, incomplete digestion and a 15-kDa fragment results. Antibody binding to the N-terminal of rEppin did not affect rSg digestion. Addition of antibodies to the C-terminal of rEppin inhibited the modulating effect of rEppin. Conclusion： Eppin protects a 15-kDa fragment of rSg from hydrolysis by PSA.