The impact of paternal age on cumulative assisted reproductive technology outcomes

Objective

To investigate the impact of paternal age on cumulative live birth rate in ART.

Design

Retrospective single-center cohort study.

Patients

All female patients aged 18-43 years and male patients aged 18-60 years, who performed their first ART cycle between January 2018 and December 2020, were included.

Main outcome measures

The primary outcome, cumulative live birth rate (cLBR), was estimated following fresh or frozen embryo transfers issued from an ART cycle. Secondary outcomes included the cumulative pregnancy rate (cPR) and miscarriage rate. Subgroup analyzes were performed as follows: men <45 and ≥ 45; female <35, 35-38, and > 38 years.

Results

A total of 2,358 couples were included in this study. The sperm quantity of male patients within both age groups was divided in two groups: normal and abnormal, which were found to be in significantly equal proportions. There were significantly fewer current smokers in the male group ≥45. The cPR was 0.5301 in the group <45 and 0.3111 in the group ≥45, with a p-value <0.001. Analysis according to the female age revealed that, in the female group >38, the cLBR rate was 0.26 for men <45 and 0.19 for men ≥45, with a p-value of 0.061. Additionally, the cPR was 0.34 in the male group <45 and 0.21 in the group ≥45, with a p-value <0.001. In the female group between 35 and 38 years of age, the cLBR was 0.44 in the male group <45 and 0.3 in the male group ≥45, with a p-value of 0.031. The cPR was 0.49 in the male group <45 and 0.34 in the group ≥45, p = 0.036. Within the female group <35, we observed non-significant results. The miscarriage rate results were not significantly different for women ≤38.

Conclusion

According to the results from our study, male age ≥ 45 has a significant impact on cumulative ART outcomes.

Ovarian Follicular Response Is Altered by Salpingectomy in Assisted Reproductive Technology: A Pre- and Postoperative Case-Control Study

Objectives: The goal of this study was to assess the effect of unilateral salpingectomy on the number of mature follicles in the ipsilateral ovary during an assisted reproductive technology (ART) stimulation cycle, as compared to the contralateral ovary. Methods: This was a retrospective, single-center, case-control cohort study conducted from 2017 to 2022. Patients from 18 to 43 years old who underwent at least one ART cycle before and after a unilateral salpingectomy were included. The number of recruited follicles, including mature (≥16 mm) and intermediate follicles (13-15.5 mm), on the salpingectomy side (case) were compared to those present on the contralateral ovary (control) during an ART attempt. To take into account the inter-ovarian variability, the comparison was performed on two ART cycles, performed before then after the salpingectomy. Results: Overall, 24 patients were included in our study. While the number of mature follicles was similar in both ovaries before surgery, the mean number of mature follicles was significantly reduced after salpingectomy in the operated side, as compared to the control side, being, respectively 3.00 vs. 5.08 (p = 0.048). There was no significant difference between the intermediate and total recruited follicles. Conclusions: Our study suggests that salpingectomy may impact the follicle recruitment on the ipsilateral side by altering the vascularization during mesosalpinx coagulation. Gynecologists should be mindful of this concept and accurately set surgical indications. Beyond the indication, this emphasizes the critical role of having infertility surgeons sensitive to fertility preservation for optimal management of ART patients. Further studies with larger patient populations are required to confirm these results.

The importance of on-site genetic counseling for prospective assisted reproductive technology patients

PURPOSE

To assess the value of having an onsite genetic counseling service integrated into an assisted reproductive technology (ART) center.

METHODS

Since January 2021, we have offered genetic counseling at our ART center for couples whose medical history suggests risk of transmission of a genetic disorder. The percentage of couples referred for genetic counseling, the distribution of couples according to reasons for consultation, the mode of transmission in cases of Mendelian disorders, and the frequency of mutations for those with identified genetic disorders were determined.

RESULTS

In an 18-month period, 150 of 1340 couples (11.2%) enrolled for ART treatment were referred to the genetic counseling unit. Two-thirds (99/150, 66.0%) were referred for a known genetic risk, a family history of a genetic disorder or chromosomal abnormality, a serious condition of unknown cause, or consanguinity. The remaining couples had a putative genetic risk (diminished ovarian reserve, high incidence of oocyte immaturity, recurrent abortion, or severe male infertility). Of the 99 with known genetic risk, 62 (62.7%), were approved for ART treatment, 23 (23.2%) were recommended prenatal or preimplantation testing, and 14 (14.1%) were referred for further testing before undergoing ART.

CONCLUSIONS

Our findings reveal great value in having an on-site genetic counseling unit for referral of ART patients. Such a unit makes the ART process smoother and safer for couples, and it lightens the burden of ART staff by removing responsibilities for which they are neither trained, nor should they have to assume.

Are There Ovarian Responsive Indexes That Predict Cumulative Live Birth Rates in Women over 39 Years?

Objective: Ovarian response indexes have been proposed in assisted reproductive technology (ART) in order to optimize live birth rates (LBR), adjusting ovarian stimulation (OS), and minimizing risks. Gonadotropin doses are commonly adjusted according to ovarian reserve parameters, including antral follicle count (AFC), anti-Mullerian hormone (AMH), and basal follicle stimulating hormone (FSH) levels. The retrospective assessment of ovarian responses allows one to identify three primary indexes: (i) follicular output rate (FORT), the ratio of the number of pre-ovulatory follicles obtained at OS completion over AFC; (ii) follicle oocyte index (FOI), the ratio of oocytes retrieved over AFC; (iii) ovarian sensitivity index (OSI), the ratio of oocytes retrieved over the total gonadotropin dose administered. In recent publications, these indexes were reported to predict ART outcome. In the present study, we assessed the ability of these indexes to predict cumulative ART outcome in women ≥39 years. Materials and Methods: Retrospective cohort study. All patients ≥39 years who performed their first ART cycle with an antagonist protocol in our center between 01/2018 and 04/2020 were included. Patients with basal FSH > 20 IU/l, AMH < 0.1 ng/mL and severe male factors (azoospermia with testicular biopsy) were excluded. All patients received both recombinant FSH and human menopausal gonadotropin (hMG). Cumulative live birth rate (cLBR) was the primary outcome. Secondary outcomes included: the number of MII oocytes, cumulative implantation (cIR), and usable blastulation rates. Logistic regressions were performed to assess the predictive values of FORT, FOI, and OSI in cLBR and embryo culture success. For each parameter, the ability of the logistic regression models to predict embryo culture success was quantified by the area under the ROC curve (AUC). Only the significant findings related to FORT, FOI, and OSI were included in the multiple logistic regression model. Linear regression models were performed between cIR, cLB, FORT, FOI, and OSI. Each statistic model was adjusted for age. Concerning OR for OSI, values were multiplied *100 due to the very low value. Results: 429 patients met the inclusion criteria. There were 298 obtained usable blastocysts after ART treatment. Age-adjusted OSI was significantly associated with cLBR [OR = 17.58 95% CI (5.48−56.40), AUC = 0.707 95% CI (0.651−0.758)) and cIR (beta = 30.22 (SE: 7.88), p < 0.001, R2= 0.060). Both FOI (OR = 6.33 95% CI (3.27−12.25), AUC = 0.725 95% CI (0.675−0.771), R2 = 0.090, p < 0.001) and OSI (OSI*100; OR = 1808.93 95% CI (159.24−19,335.13), AUC = 0.790 95% CI (0.747−0.833), R2 = 0.156, p < 0.001) were independently, when age adjusted, associated with embryo culture success. OSI showed a main performance to explain successful embryo culture than FOI (R2 = 0.156 vs. R2 = 0.090, p < 0.001). In the age-adjusted linear regression model, FOI (R2 = 0.159, p < 0.001), OSI (R2 = 0.606, p < 0.001), and FORT (r2 = 0.030, p < 0.001) were predictive of the number of MII oocytes collected. Furthermore, for OSI (r2 = 0.759, p < 0.001) and FOI (r2 = 0.297, p < 0.001), the correlation with the number of metaphase II oocytes collected was significantly higher in the non-linear regression model. Conclusions: Our findings suggest that the best index, among those analyzed, to predict cIR and cLBR, is OSI. Both OSI and FOI predict embryo culture with success, but OSI is more accurate. OSI, FOI, and FORT are significantly related to the number of MII oocytes obtained.

Impact of Ovarian Yield-Number of Total and Mature Oocytes Per Antral Follicular Count-On Live Birth Occurrence After IVF Treatment

To assess the relation between oocytes yield including total retrieved oocytes (O)c and total mature oocytes (MII) relative to the antral follicular count (AFC) (3–9 mm in diameter) and relative to anti-müllerian hormone (AMH) ng/mL level: Oc/AFC, MII/AFC, Oc/AMH, and MII/AMH, respectively, and ART outcomes. We included retrospectively 264 IVF cycles after the first embryo transfer (ET) and after the cumulative ET (CET). The implantation rate (IR) and the live birth rate (LBR) after first ET were 31 ± 39% and 32.6%, respectively, and after CET 35 ± 38% and 45.1%, respectively. There was a significantly higher average of Oc/AFC and MII/AFC when live birth (LB) occurred after the first ET (0.82 ± 0.4 vs. 0.71 ± 0.35 and 0.57 ± 0.4 vs. 0.68 ± 0.3, respectively, P < 0.05). We reported a significantly higher average of MII/AFC when LB occurred after CET (0.66 ± 0.3 vs. 0.56 ± 0.30, P = 0.02) in comparison to the group where no LB was obtained. Increased Oc/AFC and MII/AFC ratios were associated with the occurrence of LB and increased IR after first ET (P < 0.05). Increased MII/AFC ratio was associated with the occurrence of LB and IR after CET (P = 0.02 and P = 0.04, respectively). After age-adjusted multivariate analyses, all these trends were confirmed (P < 0.05) except for the effect of MII/AFC ratio on IR after CET. In conclusion, Oc/AMH and MII/AMH ratios have no effect on the occurrence of LBR or on IR after first ET or CET at either age grouping. Ratios Oc/AFC and MII/AFC seem promising indicators to assess ovarian response.

P–793 Validation of French in vitro fertilization (IVF) guideline during Covid–19 pandemic by the research of Sars-Cov–2 RNA in the follicular fluid (FF) after egg retrieval

Study question

Is it possible to find viral Sars-Cov–2 RNA in FF of women undergoing treatment during Covid–19 pandemic that may compromise gamete and embryo safety?

Summary answer

No viral RNA was detected in tested FF of women undergoing IVF in compliance with recommendations. This was reassuring and supported good medical practice.

What is known already

Risks due to SARS-CoV–2 during IVF remain difficult to assess despite the screening recommended by French health authorities based on a symptom questionnaire of the couple (systematic testing by RT-PCR for the virus before egg retrieval (ER) is not mandatory). In this context, this is a real challenge for IVF laboratory to guarantee procedure, patients, gametes and embryos safety. Most studies have reported the absence of virus in sperm. No data are available for FF and only one study looked for the presence of the virus in oocytes of Covid-affected patients (Barragan M et al, 2020).

Study design, size, duration

Between June 17 and September 24, 2020, FF of consenting women were prospectively collected and symptom questionnaire recorded. During this period, women undergoing IVF in our center did not benefit from systematic PCR testing for the virus within 72 hours prior to ER through our health authorities’ recommendations. All collected FF were retrospectively tested to research viral RNA by RT-PCR and patients were recalled to answer an epidemiological follow-up questionnaire.

Participants/materials, setting, methods

For all couples, symptom questionnaires were prospectively recorded and verified at each step of IVF procedure. For all consenting women, a sample of 1 ml of FF was collected the day of ER and stored at –80 °C. After thawing, a Sars-Cov2 multiplex RT-PCR using CFX96 (Biorad*) was performed, after RNA extraction using Nimbus (Seegene*). A comprehensive epidemiological evaluation was made afterwards by phone interview and data were recorded and analyzed.

Main results and the role of chance

A total of 183 women was included out of the 214 treated during this period (85.5%). Retrospective epidemiological evaluation showed that 8 patients contracted Covid more than 2 months before the ER, 6 more than 2 months after and only one patient 1 month after ER (diagnosis based on pathognomonic signs as agueusia and anosmia or/and positive PCR ). We observed a prevalence of symptomatic Covid forms in our IVF population of 8.2% during a 6-month period surrounding their IVF cycle. Moreover, until the introduction of systematic testing by RT-PCR for the virus before ER since the end of September 2020, 3 patients have been cancelled out of the 403 planned for positive PCR despite a negative questionnaire, which represents a prevalence of asymptomatic forms on the day of the ER at 0.7%. All the 183 FF tested did not reveal any viral RNA detection, which was reassuring concerning our medical practice and patient compliance and transparency. The absence of detected viral RNA may be due to several reasons: 1) women were not infected the day of ER 2) women had an asymptomatic form of the disease with low viral load 3) FF is not a virus reservoir.

Limitations, reasons for caution

Not all patients were included (85.5%). Post-diagnosis stays uncertain because PCR tests at the beginning of the epidemic were not mandatory and hardly available.

Wider implications of the findings: The absence of viral RNA in FF of women only screened through a symptom questionnaire is reassuring concerning the safety of IVF during Covid pandemic.

Trial registration number

Not applicable

The Mare: A Pertinent Model for Human Assisted Reproductive Technologies?

Although there are large differences between horses and humans for reproductive anatomy, follicular dynamics, mono-ovulation, and embryo development kinetics until the blastocyst stage are similar. In contrast to humans, however, horses are seasonal animals and do not have a menstrual cycle. Moreover, horse implantation takes place 30 days later than in humans. In terms of artificial reproduction techniques (ART), oocytes are generally matured in vitro in horses because ovarian stimulation remains inefficient. This allows the collection of oocytes without hormonal treatments. In humans, in vivo matured oocytes are collected after ovarian stimulation. Subsequently, only intra-cytoplasmic sperm injection (ICSI) is performed in horses to produce embryos, whereas both in vitro fertilization and ICSI are applied in humans. Embryos are transferred only as blastocysts in horses. In contrast, four cells to blastocyst stage embryos are transferred in humans. Embryo and oocyte cryopreservation has been mastered in humans, but not completely in horses. Finally, both species share infertility concerns due to ageing and obesity. Thus, reciprocal knowledge could be gained through the comparative study of ART and infertility treatments both in woman and mare, even though the horse could not be used as a single model for human ART.

Is there a link between plasma progesterone 1-2 days before frozen embryo transfers (FET) and ART outcomes in frozen blastocyst transfers?

OBJECTIVE

To study the efficacy of combined administration of subcutaneous and vaginal progesterone for priming frozen blastocysts transfers, looking at progesterone levels and ART outcome.

DESIGN

Retrospective study.

SETTING PATIENTS

Three hundred and twenty frozen blastocyst transfer cycles conducted in 213 women aged up to 42 years, BMI between 18 and 30 kg/m², with anatomically normal uterus who underwent frozen embryo transfers (FETs) from February 2019 to December 2019 with a combined luteal-phase support (LPS) associating subcutaneous and vaginal progesterone. Patients with recurrent pregnancy loss (RPL) were excluded.

RESULTS

When using combined vaginal and subcutaneous LPS, SPL >10.50 ng/mL in 95% of cases, with a minimum value of 7.02 ng/mL. CPR, OPR, and global miscarriage rates were 38.4%, 30.9%, and 19.5%, respectively. Analyzing results per quartiles, revealed that miscarriage rates were significantly inferior, and IR were higher in the upper two quartiles of serum progesterone (>21.95 ng/mL) on the day before FET, while there was no difference in CPR and OPR.

CONCLUSIONS

We report ART outcome of frozen blastocyst transfers performed using a combination of vaginal and subcutaneous progesterone for LPS. ART results were honorable and SPL favorable 1-2 days before FET in 99% of cases.

Utilization of in vitro maturation in cases with a FSH receptor mutation

PURPOSE

To identify the FSH receptor (FSHR) variant and efficacy of in vitro maturation (IVM) in a 28-year-old woman with secondary amenorrhea, primary infertility, and ovarian resistance to FSH, and to analyze the genotype-to-phenotype relationship in cases of FSHR mutation for the development of an IVM algorithm for use in patients with gonadotropin resistance syndrome (GRS).

METHODS

Oocytes retrieved after menstruation induction with norethisterone, followed by daily estrogen and an ovulatory trigger, underwent IVM, ICSI, and culture in a time-lapse (TL) incubator. Embryo transfers were performed on day 2, and after thawing on day 5. Genes associated with disorders of sex development were sequenced for both the patient and her parents. All reported cases of FSHR mutation were analyzed to investigate genotype/phenotypic relationships.

RESULTS

After ovum pickup, seven of 16 oocytes matured and all fertilized. After unsuccessful day 2 transfer, our patient delivered with a thawed day 5 blastocyst, the sole embryo without abnormal TL phenotypes. Genetic analysis revealed a new composite heterozygous FSHR variant. Analysis of our patient case with published cases of GRS revealed associations among FSHR variant genotype, location on the FSHR, functionality of tested variants, and type of amenorrhea. An algorithm for application of IVM for GRS patients was developed.

CONCLUSIONS

We report two novel variants of the FSHR. Although IVM successfully matured some oocytes, only one resulted in an embryo with normal TL phenotypes. We recommend FSHR genetic testing in GRS patients, which will help guide their suitability for IVM.

Signal processing for the detection of multiple imperfection echoes drowned in the structural noise

In this work, we propose to develop algorithms based on the split spectrum processing method associated with the multi-steps method based on "Group delay moving entropy" (GDME) allowing detecting and locating multiple imperfection echoes drowned in the structural noise of materials. In fact, GDME is based on the fact that defect echoes have a constant group delay while the noise has a random group delay. The investigation is performed with 4 known defect echoes with different characteristics (position, center frequency and bandwidth). The defect echo frequency is varied around the frequency of the input signal in order to evaluate, by signal to noise ratio calculation, the robustness of the detection method. The grain noise signal is generated first, by a simple clutter model which consider the noise, in the time domain, as the superimposed of signal coming from backscaterers in the medium and second, experimentally by a material with coarse grains.

Hemodynamic and echocardiographic effects of hemofiltration performed during cardiopulmonary bypass

OBJECTIVE

To evaluate the effects of hemofiltration performed during rewarming before emergence from cardiopulmonary bypass on hemodynamic and echocardiographic parameters.

DESIGN

Prospective randomized study; blind analysis of echocardiographic parameters and hemodynamic parameters.

SETTING

Single-center study performed in a university hospital.

PARTICIPANTS

Two groups of 13 adult patients undergoing coronary artery bypass graft surgery.

INTERVENTION

Patients were randomized to conventional procedure or hemofiltration performed with a polysulfone hemofilter. Hemofiltration, started at the time of rewarming on cardiopulmonary bypass, was performed with a flow rate adjusted to achieve an ultrafiltrate volume of 15 mL/kg on completion of rewarming.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic (systemic mean arterial pressure, right atrial pressure, heart rate) and echocardiographic parameters (shortening fraction, segmental kinetic score, cardiac output, systemic vascular resistance) were measured before and after hemofiltration and on arrival in the intensive care unit. Heart rate and cardiac index were increased significantly in both groups during the postoperative period. In the control group, systemic vascular resistance was decreased significantly, and cardiac index was increased during the postoperative period, together with significant alterations of segmental kinetic score and shortening fraction. In the hemofiltration group, systemic vascular resistance remained unchanged, associated with a significantly improved segmental kinetic score compared with the control group.

CONCLUSIONS

Hemofiltration performed during rewarming before emergence from cardiopulmonary bypass is associated with stability of hemodynamic parameters and improved segmental myocardial kinetics.

Correlation of flow cytometry to clinical factors, hormone receptors, and histopathological grade in stage I and II invasive breast carcinoma

DNA index (ploidy) and S-phase fraction (SPF) were measured by flow cytometry in 131 invasive stage I and II breast carcinomas. Ploidy showed a strong correlation with SPF (p = 0.0001), with aneuploid tumors having a high SPF. Both cytometric parameters correlated with tumor size and hormonal receptor status. Smaller tumors tended to be diploid and have low SPF. Nodal status did not demonstrate an association with cytometric findings. There was a highly significant connection between tumor grade, especially nuclear grade, and SPF (p = 0.0001). The study demonstrates the relationship between conventional prognostic factors, DNA content, and proliferative activity of breast tumors.

Does pathologic node status affect local control in patients with carcinoma of the head and neck treated with radical surgery and postoperative radiotherapy?

PURPOSE

To evaluate the effect of pathologic lymph node status and nodal stage on local control at the primary site in patients with advanced squamous cell carcinomas of the head and neck, treated with radical surgery and postoperative irradiation.

METHODS AND MATERIALS

Fifty-seven patients with advanced squamous cell carcinomas of the oral cavity, oropharynx, hypopharynx, larynx, and supraglottic larynx were analyzed. All patients underwent resection of the primary lesion, neck dissection, and postoperative radiotherapy. Minimum follow-up was 2 years. The median dose to the primary tumor bed was 60.4 Gray (range 39.7-72.0). Besides pathologic nodal status (pN0 vs. pN+) and nodal stage, the following factors were analyzed for their impact on local control: age, gender, T stage, tumor grade, resection margins, interval from surgery to irradiation, dose to the primary site, and overall treatment time.

RESULTS

The 3-year actuarial local control rate was 78%. When all patients were analyzed, nodal status (pN0 vs. pN+) did not affect control at the primary site (71% vs. 82%, p = 0.42). Nodal stage (pN0-N2a va. pN2b-N2c) was also not a significant factor for local control (74% vs. 82%, p = 0.57). When only patients with negative margins were analyzed, nodal status again did not impact on local control (79% vs. 90% for pN0 vs. pN+, p = 0.39). On univariate analysis, only tumor grade, margin status, and elapsed days were significant factors for local control. Local control was 85% for patients with negative margins vs. 60% for those with positive margins (p = 0.016). For patients with moderately and poorly differentiated tumors, local control was 86% as compared to 50% for patients with well-differentiated tumors (p = 0.007). When radiotherapy was completed within 50 days, local control was 93% as opposed to 63% for > 50 days (p = 0.016). On multivariate analysis, only margin status (p = 0.002) and tumor grade (p = 0.007) remained significant.

CONCLUSION

We conclude that neither the presence of pathologically positive nodes nor nodal stage is a prognostically significant factor for local control in patients who have undergone radical surgery and postoperative radiotherapy for advanced squamous cell carcinomas of the head and neck. We do not recommend a change in treatment philosophy, such as an increase in dose to the primary site, based on the pathologic status of the neck.

Prognostic factors for local control and survival in T1 squamous cell carcinoma of the glottis

PURPOSE

To evaluate the effect of host, tumor, and treatment-related variables on local control and survival in patients with T1N0M0 squamous cell carcinoma of the glottis.

MATERIALS AND METHODS

Ninety-one patients with T1N0M0 squamous cell carcinoma of the glottic larynx were analyzed. Median follow-up was 9 years (range 2-25). Patients were treated with daily fractions of 180 cGy to 220 cGy to doses of 5925-7000 cGy (median 6400). The following factors were analyzed: age, sex, histologic grade, disease extent, beam energy, field size, total dose, dose per fraction, and elapsed treatment days.

RESULTS

The 5-year actuarial local control was 80%. On univariate analysis, only elapsed treatment days and dose per fraction were significant factors for local control. Local control was 100% if treatment was completed within 42 days, 91% for 43-46 days, 74% for 47-50 days, 65% for 51-54 days, and 50% for 55-66 days (p = 0.0001). In patients treated at < 200 cGy per fraction, local control was 62% as compared to 87% for > or = 200 cGy per fraction (p = 0.006). On multivariate analysis, only elapsed treatment days was a significant factor for local control (p = 0.0001). The 5-year actuarial survival for the whole group was 92%. Elapsed treatment days was the only variable affecting survival. Survival was 100% if treatment was delivered within 42 days, 96% for 43-46 days, 94% for 47-50 days, 91% for 51-54 days, and 67% for 55-66 days (p = 0.02). The 5-year actuarial disease-specific survival was 95%, with treatment duration again being the only significant prognostic factor. Disease-specific survival was 97% for treatment completed within 39-54 days versus 80% for 55-66 days (p = 0.02). Only three (3.3%) patients experienced moderate or severe complications. None of the evaluated parameters impacted significantly on complications.

CONCLUSION

We conclude that elapsed days is the most prognostically significant factor for local control and survival in patients treated with radiotherapy for T1 squamous cell carcinoma of the glottis. We recommend that these patients be treated with 210 cGy daily fractions to 6300 cGy.

Characterization of the b99 allotype of rabbit immunoglobulin kappa 1 light chain

A previously undetected allotypic specificity, A99, was found in a wild rabbit (Oryctolagus cuniculus) population in Portugal. The A99 allotype cross-reacted with anti-b6 and anti-b96 sera, but carried its own antigenic determinants and was therefore distinct from the known allotypes of the b series. The A99 determinants were located on the kappa 1 light chain of IgG molecules and were inherited as allotypic determinants of the b series. Taken together, these data provide evidence that A99 is encoded by an allele at the b locus, tentatively designated b99. The great similarity between the b6, b96 and b99 allotypes suggests that they derived from a common ancestor.

Mouse monoclonal antibodies against rabbit b6 allotype and their use for characterization of light-chain subpopulations

Mouse anti-allotypic hybridomas directed against different antigenic determinants of the b6 rabbit allotype have been raised. The fine specificity of these monoclonal antibodies (mAbs) was determined by radioimmunoassay and it was possible to classify them into three groups, each directed against distinct epitopes of the b6 allotype. Hare "b6" IgG were tested with anti-b6 mAb and no reaction was found indicating that the number of allotopes present on b6 molecules is greater than the three detected by the mAb. Comparative analysis by precipitation in gel of IgG from homozygous b6/b6 rabbits using mouse mAb and rabbit anti-b6 antibodies suggested that at least two categories of molecules can be discriminated. The observation of b6 subpopulations was confirmed by isolation of a minor subpopulation of IgG on a mouse monoclonal immunoadsorbent.

Structural studies of a wild rabbit immunoglobulin light chain constant region

The amino acid sequence of a wild rabbit light chain constant region of allotype b95 was nearly completely determined by manual and automated Edman degradation procedures. The comparison of the b95 primary structure with the other b allotypes reveals about 20% substitutions between b95 and b4, b5 and b6, and 36% between b95 and b9. The substitutions are clustered in parts of the chain in agreement with our sequence data for b5 and b6. The presence in b95 of the characteristic cysteine residue at position 170 and the tryptophane residue at position 147 is in agreement with the serological similarity of these various rabbit kappa light chains. The examination of the rate of amino acid substitutions between the b95 chains and the other b allotypes shows that b95 is closer to b4, b5 and b6 than to b9.

A second rabbit kappa isotype

Immunoglobulin G (IgG) from the rabbit strain Basilea was previously shown to contain two distinct populations of molecules one with light chain belonging to the known lambda isotype and the others to a new kappa-like L chain type. Alloantisera prepared against the Basilea IgG are directed against the kappa-like light chain (anti-bas antisera). All Basilea rabbits express kappa-like chains recognized by anti-bas sera, but IgG from other domestic rabbits did not react with these antisera. Genetic studies of wild rabbits belonging to different populations show that the bas+ phenotype could be found in heterozygous rabbits as well as those homozygous at the b locus. The gene encoding the bas+ light chain is closely linked to the b locus. Moreover, antigenic determinants recognized by anti-bas antibodies and antigenic determinants recognized by antibodies directed against allotypic determinants of the b series are located on distinct IgG molecules. These results show that there are two rabbit kappa isotypes: the kappa 1 isotype, bearing allotypic determinants of the b series, and the kappa 2 isotype, for which bas+ chain is one of the allotypic forms. The kappa 1 and kappa 2 isotypes are controlled by closely linked genes.

BASILEA rabbits express two types of immunoglobulin light chains: lambda and kappa-like

In the variant rabbit strain BASILEA, immunoglobulin G were shown to contain two distinct populations of IgG molecules whose light (L) chains belonged to the known lambda isotype and to a new kappa-like type. These two L chains differed from each other by electrophoretic, chemical, and antigenic properties. The kappa-like L chain fraction showed (i) an acid-labile Asp-Pro bond at the end of the joining region and (ii) a tryptic peptide, whose amino acid sequence of the NH2-terminal 15 residues was identical to the homologous constant (C) region sequence of b9 kappa chain with the exception of the residue in position 70, which is asparagine in the kappa-like chain instead of the characteristic half-cystine residue in all L chains of kappa B type expressing b4, b5, b6, or b9 allotypes. The data suggest that the kappa-like L chain component does not contain the C region half-cystine residue involved in the formation of the extra variable (V) region-C region disulfide bridge in L chains of the kappa B [Rejnek, J., Appella, E., Mage, R. G. & Reisfeld, R. A. (1969) Biochemistry 8, 2712-2718]. The partial NH2-terminal amino acid sequence of the C region of the kappa-like L chain was shown to be markedly different from b4, b6, or b9 region sequences and from rabbit lambda C region sequence. Taken together, the chemical data suggest that the kappa bas component represents a new subtype of kappa chain. A rabbit alloantiserum made against bas IgG and adsorbed with IgG fractions showing b4, b5, b6, b95, and b96 L chain allotypes appeared to be directed against the kappa-like L chain component of BASILEA IgG exclusively. All BASILEA animals expressed IgG molecules containing kappa-like chains; in contrast, IgG molecules derived from the standard domestic rabbit did not react with this antiserum.

Rabbit immunoglobulin allotypes: cross-reactivities of the b95 and b96 allotypic specificities with the allotypes of the b series present in domestic rabbits

In a population of wild rabbits originating from the Island of Zembra (Tunisia), several unknown allotypic specificities of the b series have been detected and two of them, b95 and b96, have already been described. In order to learn about their relationship with other allotypes of the same series and present in the domestic rabbit, a study of b95 and b96 cross-reactions with heterologous antisera was undertaken. From the data presented in this paper, it can be concluded that the b96 allotype is very closely related to the b6 allotype, which suggests that they are encoded by real structural genes at the b locus as presumed for b4 and b4var allotypes; the b95 allotype, which behaves as an intermediate form, can be considered as an ancestral allotype.

An 8th rabbit b allotype (b92) detected by a genetic study

Genetic study of the progeny of a Spanish wild rabbit has revealed 2 unknown allotypic specificities that behave as encoded by alleles at the b locus. One of these A92 is described in this paper. This specificity is located on immunoglobulin light chains and cross-reacts with anti-b4 and presumably with anti-b9 sera. These data indicate that A92 is a "new" allotype of the b series and is thus designated b92.

An 8th rabbit b allotype (b92) detected by a genetic study

Genetic study of the progeny of a Spanish wild rabbit has revealed 2 unknown allotypic specificities that behave as encoded by alleles at the b locus. One of these A92 is described in this paper. This specificity is located on immunoglobulin light chains and cross-reacts with anti-b4 and presumably with anti-b9 sera. These data indicate that A92 is a "new" allotype of the b series and is thus designated b92.

B 96, a seventh allele at the rabbit kappa chain b locus

A previously undetected allotypic specificity, A96, was observed in the wild rabbit population of Zembra (Tunisia). The A96 allotype is inherited as a b allotype, and its antigenic determinants are located on the kappa light chains of immunoglobulins. Although cross-reacting with b6, the A96 allotype carries its own allotypic determinants, and is therefore distinct form the known allotypes of the b series (b4, b5, b6, b9, b4var and b95). The data indicate that A96 is encoded by an allele at the b locus, tentatively designated b 96.

A and b allotypy in Oryctolagus and Lepus species

It had been previously shown by the description in wild rabbits Oryctolagus cuniculus of unknown allotypic specificities belonging to the a series and the b series, that the genetic polymorphism found in domestic rabbits was only a part of the genetic polymorphism of the species O. cuniculus. To the known a1, a2 and a3 allotypic specificities have been added in the last years a100 and a101 which are under the control of allelic genes at the a locus. Studies of cross-reactivities in the a system is a way to detect variants of a given allotypic specificity. The phylogenetic studies in the hare Lepus capensis demonstrate that a2 and a3 determinants are allotypic, apparently without polymorphism in this species; indeed, all the tested hares have either a2 or a3 determinants or both. Four presumably "new" allotypic specificities of the b series, A93, A94, A95 and A96 have been found in a population of wild rabbits O. cuniculus from an Island in Tunisia. A95 allotypic specificities against which specific antisera have been prepared, shows cross-reactivities with b4, b5 and b6 allotypes of domestic rabbit. Genetic data demonstrate that A95 is indeed under the control of an allele at the b locus. If schematic mechanisms involving duplication and mutations of genes are suitable to understand the presence of variants and their cross-reactivities, one has to understand how so many genes are involved in allotypy and how it remains stable during evolution.