Automated prostate gland segmentation in challenging clinical cases: comparison of three artificial intelligence methods

OBJECTIVE

Automated methods for prostate segmentation on MRI are typically developed under ideal scanning and anatomical conditions. This study evaluates three different prostate segmentation AI algorithms in a challenging population of patients with prior treatments, variable anatomic characteristics, complex clinical history, or atypical MRI acquisition parameters.

MATERIALS AND METHODS

A single institution retrospective database was queried for the following conditions at prostate MRI: prior prostate-specific oncologic treatment, transurethral resection of the prostate (TURP), abdominal perineal resection (APR), hip prosthesis (HP), diversity of prostate volumes (large ≥ 150 cc, small ≤ 25 cc), whole gland tumor burden, magnet strength, noted poor quality, and various scanners (outside/vendors). Final inclusion criteria required availability of axial T2-weighted (T2W) sequence and corresponding prostate organ segmentation from an expert radiologist. Three previously developed algorithms were evaluated: (1) deep learning (DL)-based model, (2) commercially available shape-based model, and (3) federated DL-based model. Dice Similarity Coefficient (DSC) was calculated compared to expert. DSC by model and scan factors were evaluated with Wilcox signed-rank test and linear mixed effects (LMER) model.

RESULTS

683 scans (651 patients) met inclusion criteria (mean prostate volume 60.1 cc [9.05-329 cc]). Overall DSC scores for models 1, 2, and 3 were 0.916 (0.707-0.971), 0.873 (0-0.997), and 0.894 (0.025-0.961), respectively, with DL-based models demonstrating significantly higher performance (p < 0.01). In sub-group analysis by factors, Model 1 outperformed Model 2 (all p < 0.05) and Model 3 (all p < 0.001). Performance of all models was negatively impacted by prostate volume and poor signal quality (p < 0.01). Shape-based factors influenced DL models (p < 0.001) while signal factors influenced all (p < 0.001).

CONCLUSION

Factors affecting anatomical and signal conditions of the prostate gland can adversely impact both DL and non-deep learning-based segmentation models.

Laser enucleation of the prostate (LEP) vs. simple prostatectomy: an analysis of hospital charges and comparison of practice trends

PURPOSE

Laser enucleation of the prostate (LEP) and simple prostatectomy (SP) are surgical treatment options for large gland Benign Prostatic Hyperplasia. While multiple studies compare clinical outcomes of these procedures, there are limited data available comparing hospital charges in the United States. Here, we present current practice trends and a hospital charge analysis on a national level using an annual insurance claims data repository.

METHODS

The Healthcare Cost and Utilization Project National Inpatient Sample and Nationwide Ambulatory Surgery Sample databases for 2018 were queried. CPT and ICD-10PCS codes identified patients undergoing LEP or SP, who were then compared for practice setting, total hospital charges, and payor. Laser type for LEP and surgical approach for SP could not be differentiated.

RESULTS

The median hospital charge of 5782 LEPs and 973 SPs is $26,689 and $51,250 (p < 0.001), respectively. LEP independently predicts a decreased hospital charge of $16,464 (p < 0.001) per case. Medicare is the primary payor for both procedures. More LEP procedures are completed in the outpatient setting (87.8%) vs. SPs (5.7%, p < 0.001). Median length of stay is longer for SP (LEP: 0, IQR: 0; SP: 3, IQR: 2-4; p < 0.001). In the Western region, LEP is least commonly performed (184, p < 0.001), most expensive ($43,960; p < 0.001), and has longer length of stay (2, p < 0.001).

CONCLUSIONS

LEP should be considered a cost-effective alternative to SP. Regions of the U.S. that perform more LEPs have shorter length of stay and lower hospital charges associated with the procedure.

A Cascaded Deep Learning-Based Artificial Intelligence Algorithm for Automated Lesion Detection and Classification on Biparametric Prostate Magnetic Resonance Imaging

RATIONALE AND OBJECTIVES

Prostate MRI improves detection of clinically significant prostate cancer; however, its diagnostic performance has wide variation. Artificial intelligence (AI) has the potential to assist radiologists in the detection and classification of prostatic lesions. Herein, we aimed to develop and test a cascaded deep learning detection and classification system trained on biparametric prostate MRI using PI-RADS for assisting radiologists during prostate MRI read out.

MATERIALS AND METHODS

T2-weighted, diffusion-weighted (ADC maps, high b value DWI) MRI scans obtained at 3 Tesla from two institutions (n = 1043 in-house and n = 347 Prostate-X, respectively) acquired between 2015 to 2019 were used for model training, validation, testing. All scans were retrospectively reevaluated by one radiologist. Suspicious lesions were contoured and assigned a PI-RADS category. A 3D U-Net-based deep neural network was used to train an algorithm for automated detection and segmentation of prostate MRI lesions. Two 3D residual neural network were used for a 4-class classification task to predict PI-RADS categories 2 to 5 and BPH. Training and validation used 89% (n = 1290 scans) of the data using 5 fold cross-validation, the remaining 11% (n = 150 scans) were used for independent testing. Algorithm performance at lesion level was assessed using sensitivities, positive predictive values (PPV), false discovery rates (FDR), classification accuracy, Dice similarity coefficient (DSC). Additional analysis was conducted to compare AI algorithm's lesion detection performance with targeted biopsy results.

RESULTS

Median age was 66 years (IQR = 60-71), PSA 6.7 ng/ml (IQR = 4.7-9.9) from in-house cohort. In the independent test set, algorithm correctly detected 111 of 198 lesions leading to 56.1% (49.3%-62.6%) sensitivity. PPV was 62.7% (95% CI 54.7%-70.7%) with FDR of 37.3% (95% CI 29.3%-45.3%). Of 79 true positive lesions, 82.3% were tumor positive at targeted biopsy, whereas of 57 false negative lesions, 50.9% were benign at targeted biopsy. Median DSC for lesion segmentation was 0.359. Overall PI-RADS classification accuracy was 30.8% (95% CI 24.6%-37.8%).

CONCLUSION

Our cascaded U-Net, residual network architecture can detect, classify cancer suspicious lesions at prostate MRI with good detection, reasonable classification performance metrics.

Multiresolution Application of Artificial Intelligence in Digital Pathology for Prediction of Positive Lymph Nodes From Primary Tumors in Bladder Cancer

PURPOSE

To develop an artificial intelligence (AI)-based model for identifying patients with lymph node (LN) metastasis based on digital evaluation of primary tumors and train the model using cystectomy specimens available from The Cancer Genome Atlas (TCGA) Project; patients from our institution were included for validation of the leave-out test cohort.

METHODS

In all, 307 patients were identified for inclusion in the study (TCGA, n = 294; in-house, n = 13). Deep learning models were trained from image patches at 2.5×, 5×, 10×, and 20× magnifications, and spatially resolved prediction maps were combined with microenvironment (lymphocyte infiltration) features to derive a final patient-level AI score (probability of LN metastasis). Training and validation included 219 patients (training, n = 146; validation, n = 73); 89 patients (TCGA, n = 75; in-house, n = 13) were reserved as an independent testing set. Multivariable logistic regression models for predicting LN status based on clinicopathologic features alone and a combined model with AI score were fit to training and validation sets.

RESULTS

Several patients were determined to have positive LN metastasis in TCGA (n = 105; 35.7%) and in-house (n = 3; 23.1%) cohorts. A clinicopathologic model that considered using factors such as age, T stage, and lymphovascular invasion demonstrated an area under the curve (AUC) of 0.755 (95% CI, 0.680 to 0.831) in the training and validation cohorts compared with the cross validation of the AI score (likelihood of positive LNs), which achieved an AUC of 0.866 (95% CI, 0.812 to 0.920; P = .021). Performance in the test cohort was similar, with a clinicopathologic model AUC of 0.678 (95% CI, 0.554 to 0.802) and an AI score of 0.784 (95% CI, 0.702 to 0.896; P = .21). In addition, the AI score remained significant after adjusting for clinicopathologic variables (P = 1.08 × 10^-9), and the combined model significantly outperformed clinicopathologic features alone in the test cohort with an AUC of 0.807 (95% CI, 0.702 to 0.912; P = .047).

CONCLUSION

Patients who are at higher risk of having positive LNs during cystectomy can be identified on primary tumor samples using novel AI-based methodologies applied to digital hematoxylin and eosin-stained slides.

Rapidly Progressing Urothelial Carcinoma Due to a Rare TP53 (p.Arg110Pro) Mutation: A Case Report and Review of the Literature

We present a case of a 69-year-old male patient diagnosed with high grade (T₁ HG) urothelial carcinoma of the bladder who progressed rapidly towards muscle invasive disease and eventually death despite neoadjuvant chemotherapy and radical cystectomy. We postulate that this may be due to a deleterious underlying somatic gene mutation. Molecular pathologic data obtained on the initial, non-muscle invasive tumor and the final cystectomy specimen, revealed the same TP53 mutation (p.Arg110Pro) in both specimens with a variant allele frequency of 44%. The tumor was tested for 50 common gene mutations in urothelial carcinoma and no other identifiable DNA repair mutations were found, suggesting that this specific TP53 aberration, one that has never been reported in the bladder cancer literature, could be particularly deleterious. Knowing that bladder cancer cell lines that lack TP53 are more resistant to cisplatin and because the tumor lacked any other DNA mutation, this patient may have been a candidate for upfront surgery without neoadjuvant chemotherapy. In addition to histological analysis of the tumor, early molecular and cytogenetic characterization of resected tissue is essential in predicting progression and eventual prognosis of the disease based on identifiable gene mutations. Further comparative prospective studies are required to clarify the importance of molecular heterogeneity and subtyping in bladder cancer.

Comprehensive genomic profiling of metastatic collecting duct carcinoma, renal medullary carcinoma, and clear cell renal cell carcinoma

INTRODUCTION AND OBJECTIVE

Unlike clear cell renal cell carcinoma (CCRCC), collecting duct carcinoma (CDC) and renal medullary carcinoma (RMC) are rare tumors that progress rapidly and appear resistant to current systemic therapies. We queried comprehensive genomic profiling to uncover opportunities for targeted therapy and immunotherapy.

MATERIAL AND METHODS

DNA was extracted from 40 microns of formalin-fixed, paraffin-embedded specimen from relapsed, mCDC (n = 46), mRMC (n = 24), and refractory and metastatic (m) mCCRCC (n = 626). Comprehensive genomic profiling was performed, and Tumor mutational burden (TMB) and microsatellite instability (MSI) were calculated. We analyzed all classes of genomic alterations.

RESULTS

mCDC had 1.7 versus 2.7 genomic alterations/tumor in mCCRCC ( = 0.04). Mutations in VHL (P < 0.0001) and TSC1 (P = 0.04) were more frequent in mCCRCC. SMARCB1 (P < 0.0001), NF2 (P = 0.0007), RB1 (P = 0.02) and RET (P = 0.0003) alterations were more frequent in mCDC versus mCCRCC. No VHL alterations in mRMC and mCDC were identified. SMARCB1 genomic alterations were significantly more frequent in mRMC than mCDC (P = 0.0002), but were the most common alterations in both subtypes. Mutations to EGFR, RET, NF2, and TSC2 were more frequently identified in mCDC versus mRMC. The median TMB and MSI-High status was low with <1% of mCCRC, mCDC, and mRMC having ≥ 20 mut/Mb.

CONCLUSION

Genomic alteration patterns in mCDC and mRMC differ significantly from mCCRCC. Targeted therapies for mCDC and mRMC appear limited with rare opportunities to target alterations in receptor tyrosine kinase and MTOR pathways. Similarly, TMB and absence of MSI-High status in mCDC and mRMC suggest resistance to immunotherapies.

Determination of disease severity in COVID-19 patients using deep learning in chest X-ray images

PURPOSE

Chest X-ray plays a key role in diagnosis and management of COVID-19 patients and imaging features associated with clinical elements may assist with the development or validation of automated image analysis tools. We aimed to identify associations between clinical and radiographic features as well as to assess the feasibility of deep learning applied to chest X-rays in the setting of an acute COVID-19 outbreak.

METHODS

A retrospective study of X-rays, clinical, and laboratory data was performed from 48 SARS-CoV-2 RT-PCR positive patients (age 60±17 years, 15 women) between February 22 and March 6, 2020 from a tertiary care hospital in Milan, Italy. Sixty-five chest X-rays were reviewed by two radiologists for alveolar and interstitial opacities and classified by severity on a scale from 0 to 3. Clinical factors (age, symptoms, comorbidities) were investigated for association with opacity severity and also with placement of central line or endotracheal tube. Deep learning models were then trained for two tasks: lung segmentation and opacity detection. Imaging characteristics were compared to clinical datapoints using the unpaired student's t-test or Mann-Whitney U test. Cohen's kappa analysis was used to evaluate the concordance of deep learning to conventional radiologist interpretation.

RESULTS

Fifty-six percent of patients presented with alveolar opacities, 73% had interstitial opacities, and 23% had normal X-rays. The presence of alveolar or interstitial opacities was statistically correlated with age (P = 0.008) and comorbidities (P = 0.005). The extent of alveolar or interstitial opacities on baseline X-ray was significantly associated with the presence of endotracheal tube (P = 0.0008 and P = 0.049) or central line (P = 0.003 and P = 0.007). In comparison to human interpretation, the deep learning model achieved a kappa concordance of 0.51 for alveolar opacities and 0.71 for interstitial opacities.

CONCLUSION

Chest X-ray analysis in an acute COVID-19 outbreak showed that the severity of opacities was associated with advanced age, comorbidities, as well as acuity of care. Artificial intelligence tools based upon deep learning of COVID-19 chest X-rays are feasible in the acute outbreak setting.

Artificial intelligence for the detection of COVID-19 pneumonia on chest CT using multinational datasets

Chest CT is emerging as a valuable diagnostic tool for clinical management of COVID-19 associated lung disease. Artificial intelligence (AI) has the potential to aid in rapid evaluation of CT scans for differentiation of COVID-19 findings from other clinical entities. Here we show that a series of deep learning algorithms, trained in a diverse multinational cohort of 1280 patients to localize parietal pleura/lung parenchyma followed by classification of COVID-19 pneumonia, can achieve up to 90.8% accuracy, with 84% sensitivity and 93% specificity, as evaluated in an independent test set (not included in training and validation) of 1337 patients. Normal controls included chest CTs from oncology, emergency, and pneumonia-related indications. The false positive rate in 140 patients with laboratory confirmed other (non COVID-19) pneumonias was 10%. AI-based algorithms can readily identify CT scans with COVID-19 associated pneumonia, as well as distinguish non-COVID related pneumonias with high specificity in diverse patient populations.

Long-term Functional and Oncologic Outcomes of Partial Adrenalectomy for Pheochromocytoma

OBJECTIVE

To evaluate the recurrence and functional outcomes in a primarily hereditary cohort of patients undergoing partial adrenalectomy for pheochromocytoma.

METHODS

A retrospective review from a prospectively managed database of patients undergoing partial adrenalectomy from 1995 to 2018 at the National Cancer Institute was performed. Local recurrence was defined as imaging evidence of a recurrent or de novo lesion on the operative side. Steroid dependency was defined as requiring daily steroid replacement at time of last follow-up.

RESULTS

One hundred and twenty-four partial adrenalectomies, removing 162 tumors, were performed in 107 patients. Most patients had a known hereditary predisposition to develop bilateral, multifocal, and recurrent pheochromocytoma. Median tumor size was 2 cm (interquartile range (IQR) 1.5-2.8). Median follow-up was 60 months (IQR 13-131). Local recurrence occurred in 17 patients (15.8%) and were managed with active surveillance or surgery. A single patient (1/106, 0.9%) developed metastatic spread of pheochromocytoma approximately 14 years after his first of 2 partial adrenalectomies and remains alive under active surveillance. Median time to recurrence was 71 months (IQR 26-127) with 10 patients (9.3%) requiring daily steroid replacement at time of last follow-up.

CONCLUSION

Partial adrenalectomy offers excellent oncologic and functional outcomes, sparing most patients from lifelong steroid replacement therapy. Recurrences can be easily managed with repeat surgery or active surveillance via functional work-up and imaging. Partial adrenalectomy remains the recommended surgical management for patients pre-disposed to development of bilateral, multifocal and recurrent pheochromocytoma.

Emphysematous pyelonephritis: the impact of urolithiasis on disease severity

Background

Emphysematous pyelonephritis is a severe infection of the kidney associated with formation of gas in the renal parenchyma and/or collecting system. The purpose of this study was to evaluate outcomes of patients with emphysematous pyelonephritis in a contemporary cohort and to evaluate the impact of urolithiasis on disease severity.

Methods

A search of all imaging reports at University of California San Francisco (UCSF) for the term “emphysematous pyelonephritis” was undertaken from 2003–2014. Patients were included if there was clinical evidence of infection, no recent urologic instrumentation, and computerized tomography (CT) demonstrating gas in the renal parenchyma or collecting system. Clinical and laboratory variables were obtained from medical records.

Results

A total of 14 cases were identified. The majority of patients (57%) had gas confined to the collecting system. Three patients (21%) had gas in the renal parenchyma and 3 patients (21%) had gas extending into perirenal tissues. A total of 8 patients (57%) had concomitant urolithiasis. Seven patients (50%) were managed with antibiotic therapy alone while 6 patients (43%) required percutaneous drainage. No patients required immediate nephrectomy. There were no deaths. Patients with urolithiasis had less severe emphysematous pyelonephritis than patients without urolithiasis (P<0.05).

Conclusions

The majority of patients in this study had gas contained within the collecting system and were treated successfully with antibiotics alone. Percutaneous drainage was successfully utilized in patients with more advanced disease. No patients required emergent nephrectomy. Emphysematous pyelonephritis in patients with urolithiasis was less severe than in patients without urolithiasis.

Urethral Stricture Score is Associated with Anterior Urethroplasty Complexity and Outcome

PURPOSE

Several surgical techniques are available to treat anterior urethral stricture. The choice of surgical technique largely depends on the severity of stricture disease. The U-score (urethral stricture score) is based on urethral stricture characteristics, namely length (1 to 3 points), number (1 or 2 points), location (1 or 2 points) and etiology (1 or 2 points), which are tallied to provide a total score of 4 to 9 points. Our aim was to identify whether the U-score system is predictive of the surgical complexity and outcome of anterior urethroplasty.

MATERIALS AND METHODS

We retrospectively reviewed the records of all patients who underwent anterior urethroplasty from 2002 to 2012 by examining our prospectively collected urethroplasty database. We calculated the U-score and looked for an association with surgical complexity, recurrent stricture and time to recurrence. We defined recurrent stricture as the need for a secondary procedure.

RESULTS

There were 341 patients who underwent low complexity urethroplasty (anastomotic, buccal mucosal graft and augmented anterior urethroplasty) with a mean U-score of 4.7 while 48 underwent high complexity urethroplasty (double buccal mucosal graft, flap and graft/flap combination) with a mean score of 6.9. Higher U-score was predictive of higher surgical complexity (p <0.001). U-score was also significantly associated with recurrence. There was a consistent increase in the risk of recurrence with each additional U-score point. However, there was no association of U-score with time to recurrence.

CONCLUSIONS

We confirmed the validity of U-score to predict the complexity of surgery for anterior urethral strictures. For the first time to our knowledge we report an association between higher U-score and anterior urethroplasty outcome. The U-score could be used to risk stratify patients and help with perioperative counseling.

The Decline of Inpatient Penile Prosthesis over the 10-Year Period, 2000-2010

Introduction

Across all specialties, economic pressure is driving increased utilization of outpatient surgery when feasible.

Aims

Our aims were to analyze national trends of penile prosthesis (PP) surgery and to examine patient and hospital characteristics, and perioperative complications in the inpatient setting.

Methods

We analyzed data from National Inpatient Sample. Patients in NIS who underwent PP insertion between 2000 and 2010 were included.

Main Outcome Measures

Our main outcomes were the number of inpatient PP procedures, type of prosthesis, patient demographics, comorbidities, hospital characteristics, and immediate perioperative complications.

Results

There was a progressive and dramatic decline by nearly half in the number of both inflatable (IPP) and noninflatable (NIPP) inpatient insertions performed from 2000 to 2010 (P = 0.0001). The overall rate of inpatient complications for PP insertion was 13.5%. Patients with three or more comorbidities were found to have a higher risk of complications than patients with no comorbidities (OR = 1.45, 95% CI = 1.18–1.78) (P = 0.0001). Surgeries performed in high‐volume hospitals (10 or more PP cases per year) were associated with reduced risk of complications (OR = 0.6) (P < 0.0001). There was a dramatic decrease in inpatient setting for PP placement in high‐volume hospitals (32% in 2000 compared with 6% in 2010; P < 0.0001), and when compared with lower volume hospitals. NIPP was more likely performed in younger patients and in community hospitals, and less likely in white patients. Medicaid health insurance was associated with much higher rate of NIPP insertion than other types of insurance.

Conclusions

The number of PP procedures performed in the inpatient setting declined between 2000 and 2010, likely reflecting a shift toward increasing outpatient procedures. Our data also suggest a better outcome for patients having the procedure done at a high‐volume center in terms of inpatient complications. Alwaal A, Harris CR, Hussein AA, Sanford TH, McCulloch CE, Shindel AW, and Breyer BN. The decline of inpatient penile prosthesis over the 10‐year period, 2000–2010. Sex Med 2015;3:280–286.

Outcomes and timing for intervention of partial adrenalectomy in patients with a solitary adrenal remnant and history of bilateral phaeochromocytomas

OBJECTIVE

To evaluate the outcomes and timing of intervention for adrenal-sparing surgery in patients left with a solitary adrenal remnant after bilateral adrenal surgeries.

PATIENTS AND METHODS

Patients were included in the study if they had undergone bilateral adrenal surgery as a treatment for phaeochromocytoma and were left with a solitary adrenal remnant. Perioperative, functional and oncological outcomes were evaluated in 21 patients who met the inclusion criteria.

RESULTS

There was minimal perioperative morbidity and no perioperative mortality. After a median (range) follow-up of 21 (3-143) months, there were two cases of persistent disease. Ten patients (48%) required steroid supplementation upon discharge, with four subsequently discontinuing this treatment. Patients were more likely to require steroid supplementation after surgery if they underwent simultaneous adrenalectomy and contralateral partial adrenalectomy, rather than staged procedures (86 vs 40%, P = 0.02). Patients who underwent surgery for tumours > 4 cm were more likely to require long-term steroids than patients who underwent surgery for lesions < 4 cm (75 vs 18%, P = 0.05).

CONCLUSIONS

Patients left with a solitary adrenal remnant after bilateral adrenal surgery have low surgical morbidity, reasonable functional outcomes and low rates of recurrence at an intermediate follow-up period. A staged approach could decrease the immediate postoperative need for steroids, and intervention before the largest tumour reaches 4 cm could decrease the rate of long-term steroid dependence.

Detection of interleukin-1, interleukin-6, and tumor necrosis factor-alpha in the uterus during the second half of pregnancy in the mouse

This study demonstrated interleukin-1 (IL-1), IL-6, and tumor necrosis factor-alpha (TNF alpha) in the mouse uterus during the second half of pregnancy (days 9-18). High concentrations of IL-1 alpha mRNA and bioactive IL-1 were detected between days 12-17. IL-1 bioactivity decreased to very low levels as pregnancy approached parturition. IL-6 mRNA was detected from days 9-18, and IL-6 bioactivity approximately paralleled IL-1 bioactivity. High levels of IL-1 and IL-6 bioactivity, but not IL-1 or IL-6 mRNA, were detected in the placenta between days 12-17. Placental IL-1 and IL-6 also decreased to low levels near parturition. TNF alpha was expressed from days 9-17, and a peak of TNF alpha bioactivity was detected during the period immediately before parturition. TNF alpha mRNA and TNF alpha bioactivity were not detected in the placenta. On day 18, the day of parturition, the concentrations of IL-1, IL-6, and TNF alpha mRNA were very low relative to those on other pregnancy days. Immunocytochemistry with antibodies to IL-1, IL-6, and TNF alpha was used to confirm the presence of all three cytokines in uterine cells throughout the second half of pregnancy. Those data showing the kinetics of cytokine production during fetal development raise the possibility that cytokines and cytokine-induced mediators modulate cellular events during the late stages of pregnancy in the mouse.

Characterization of cells comprising murine thymocyte multicellular complexes

Characterization of complexes between thymocytes and thymic stromal cells was facilitated in the present study by demonstrating that complexes would reform if cells were incubated for 1.5 to 2 h in vitro at ambient temperature. Several immunologic approaches were used to determine the phenotype of complexed cells. Bound T cells were 97% double-positive (CD4 and CD8), 3% double-negative and greater than 99% CD3 positive by using immunoperoxidase immunohistology on cytospins. Five percent expressed the TCR beta-chain and 1 to 2% were IL-2R positive. The percentages were the same whether complexes were preformed in vivo or formed in vitro. Despite the apparent absence of single positive cells in complexes, when isolated CD4 or CD8 positive cells were tested for their ability to bind to adherent thymic macrophages, each subpopulation contained some cells which were capable of complex formation. When thymocytes were fractionated by density, steroid sensitivity or peanut agglutinin positivity then allowed to form complexes, cells with an immature phenotype had a greater propensity for complex formation. Central stromal cells all were class II MHC gene product (I-A and I-E) positive, expressed macrophage-associated Ag (B23.1 and MAC-1), were negative for cytokeratin but positive for vimentin, were reactive with a polyclonal antimacrophage serum, but did not express dendritic cell Ag (33D1). The data demonstrate that immature thymocytes bind exclusively to class II MHC gene product positive thymic macrophages. This binding step may play a role in the acquisition of T cell function in the thymus.

Characterization of cells comprising murine thymocyte multicellular complexes

Characterization of complexes between thymocytes and thymic stromal cells was facilitated in the present study by demonstrating that complexes would reform if cells were incubated for 1.5 to 2 h in vitro at ambient temperature. Several immunologic approaches were used to determine the phenotype of complexed cells. Bound T cells were 97% double-positive (CD4 and CD8), 3% double-negative and greater than 99% CD3 positive by using immunoperoxidase immunohistology on cytospins. Five percent expressed the TCR beta-chain and 1 to 2% were IL-2R positive. The percentages were the same whether complexes were preformed in vivo or formed in vitro. Despite the apparent absence of single positive cells in complexes, when isolated CD4 or CD8 positive cells were tested for their ability to bind to adherent thymic macrophages, each subpopulation contained some cells which were capable of complex formation. When thymocytes were fractionated by density, steroid sensitivity or peanut agglutinin positivity then allowed to form complexes, cells with an immature phenotype had a greater propensity for complex formation. Central stromal cells all were class II MHC gene product (I-A and I-E) positive, expressed macrophage-associated Ag (B23.1 and MAC-1), were negative for cytokeratin but positive for vimentin, were reactive with a polyclonal antimacrophage serum, but did not express dendritic cell Ag (33D1). The data demonstrate that immature thymocytes bind exclusively to class II MHC gene product positive thymic macrophages. This binding step may play a role in the acquisition of T cell function in the thymus.