High-Resolution, 3D Imaging of the Zebrafish Gill-Associated Lymphoid Tissue (GIALT) Reveals a Novel Lymphoid Structure, the Amphibranchial Lymphoid Tissue

The zebrafish is extensively used as an animal model for human and fish diseases. However, our understanding of the structural organization of its immune system remains incomplete, especially the mucosa-associated lymphoid tissues (MALTs). Teleost MALTs are commonly perceived as diffuse and scattered populations of immune cells throughout the mucosa. Yet, structured MALTs have been recently discovered in Atlantic salmon (Salmo salar L.), including the interbranchial lymphoid tissue (ILT) in the gills. The existence of the ILT was only recently identified in zebrafish and other fish species, highlighting the need for in-depth characterizations of the gill-associated lymphoid tissue (GIALT) in teleosts. Here, using 3-D high-resolution microscopy, we analyze the GIALT of adult zebrafish with an immuno-histology approach that reveals the organization of lymphoid tissues via the labeling of T/NK cells with an antibody directed to a highly conserved epitope on the kinase ZAP70. We show that the GIALT in zebrafish is distributed over at least five distinct sub-regions, an organization found in all pairs of gill arches. The GIALT is diffuse in the pharyngeal part of the gill arch, the interbranchial septum and the filaments/lamellae, and structured in two sub-regions: the ILT, and a newly discovered lymphoid structure located along each side of the gill arch, which we named the Amphibranchial Lymphoid Tissue (ALT). Based on RAG2 expression, neither the ILT nor the ALT constitute additional thymi. The ALT shares several features with the ILT such as presence of abundant lymphoid cells and myeloid cells embedded in a network of reticulated epithelial cells. Further, the ILT and the ALT are also a site for T/NK cell proliferation. Both ILT and ALT show structural changes after infection with Spring Viraemia of Carp Virus (SVCV). Together, these data suggest that ALT and ILT play an active role in immune responses. Comparative studies show that whereas the ILT seems absent in most neoteleosts ("Percomorphs"), the ALT is widely present in cyprinids, salmonids and neoteleosts, suggesting that it constitutes a conserved tissue involved in the protection of teleosts via the gills.

The use of whole-body fluorine-18-fluorodeoxyglucose positron emission tomography integrated with computed tomography for accurate staging and surveillance in the case of mucosa-associated lymphoid tissue

We present the case of a 79-year-old male, who was initially treated for mucosa-associated lymphoid tissue lymphoma (MALT lymphoma) of the right eyelid, and later for disease relapse in the stomach. During follow up, he was noted to have developed left arm nodules just medial to the proximal biceps muscle, which were found to be multiply enlarged lymph nodes on subsequent ultrasound imaging. Excisional biopsy of these nodes revealed MALT lymphoma. He was initially referred for consideration of radiation, but a restaging F-18 fluorodeoxyglucose positron emission tomography integrated with computed tomography (F-18 FDG PET/CT) further identified a focus of suspicious uptake in left calf, which was later also biopsy proven to be MALT lymphoma. His disease was upstaged as the result of this later finding, and the overall recommendation for treatment changed to favor systemic treatment with Rituximab.

Can benign lymphoid tissue changes in 18F-FDG PET/CT predict response to immunotherapy in metastatic melanoma?

BACKGROUND

An association between immune-related adverse events (irAEs) caused by immunotherapeutic agents and the clinical benefit of immunotherapy has been suggested. We retrospectively evaluated by means of 18F-FDG PET/CT lymphoid tissue changes in the mediastinal/hilar lymph nodes and the spleen in response to ipilimumab administration in metastatic melanoma.

METHODS

A total of 41 patients with unresectable metastatic melanoma underwent 18F-FDG PET/CT before the start of ipilimumab (baseline PET/CT), after two cycles (interim PET/CT) and at the end of treatment (late PET/CT). Data analysis was focused on the mediastinal/hilar lymph nodes and the spleen. The patients' best clinical response (BCR) was used as reference.

RESULTS

According to the BCR reference, 31 patients showed disease control (DC) and 10 patients showed progressive disease (PD). Mediastinal/hilar lymph node evaluation revealed that in total 4 patients in the interim or late PET/CT (10%) demonstrated a 'sarcoid-like lymphadenopathy' as response to treatment (LN-positive). All LN-positive patients responded to ipilimumab with DC. On the other hand, no significant differences between the DC and PD groups regarding both semi-quantitative and quantitative 18F-FDG PET spleen-related parameters at baseline and as response to treatment were detected.

CONCLUSION

Based on our findings, 10% patients in the interim or late PET/CT showed 'sarcoid-like lymphadenopathy' as response to treatment. All these patients showed disease control, implying a relation between the appearance of sarcoid-like lymphadenopathy and the clinical benefit of anti-CTLA-4 therapy. On the other hand, quantitative 18F-FDG PET analysis of the spleen showed a poor performance in predicting clinical benefit to ipilimumab.

18F-FDG PET/MR imaging of lymphoma nodal target lesions: Comparison of PET standardized uptake value (SUV) with MR apparent diffusion coefficient (ADC)

To compare positron emission tomography (PET) standardized uptake value (SUV) with magnetic resonance (MR) apparent diffusion coefficient (ADC) of nodal target lesions in patients with F-fluoro-2-deoxyglucose (FDG)-avid lymphomas by simultaneous PET/MR.Patients with histologically proven Hodgkin and non-Hodgkin lymphoma underwent PET/MR limited field of view of FDG-avid target nodal lesions. For PET images, a region of interest (ROI) was drawn around the target nodal lesion and the SUVmax and SUVmean was measured. For MR ADC measurements a ROI was placed over the target nodal lesion on diffusion-weighted imaging (DWI) and ADCmin and ADCmean (mean ADC) values within the ROI were recorded.Thirty-nine patients (19 women, 20 men; 13 patients with Hodgkin lymphoma and 26 with non-Hodgkin lymphoma) were included in the analysis. Sixty-six nodal lesions detected by PET/CT (19 PET-negative and 47 PET-positive) were analyzed by PET/MR. PET/MR quantitative assessments showed that ADCmin and ADCmean were accurate for discriminating positive from negative nodal lymphoma, with an AUC of 0.927 and 0.947, respectively. The ROC curve analysis of ADCmean versus SUVmax and SUVmean was not statistically significant (difference=0.044, P = .08 and difference = 0.045, P = .07; respectively). A substantial inverse association was observed between ADCmean with SUVmean and SUVmax (rho = -0.611; -0.607; P < .0001, respectively). A moderate inverse association was found between ADCmin with SUVmean and SUVmax (rho = -0.529, -0.520; P < .0001, respectively). Interobserver variability of quantitative assessment showed very good agreement for all variables (ICC>0.87).A significant correlation between ADCs and SUVs is found in FDG avid lymphomas. ADCmean is not inferior to PET SUV in discriminating positive and negative nodal lymphomas. Further larger studies are warranted to validate quantitative PET/MR for lymphoma patient management.

[18F]-Fluorodeoxyglucose Uptake in Lymphoid Tissue Serves as a Predictor of Disease Outcome in the Nonhuman Primate Model of Monkeypox Virus Infection

Real-time bioimaging of infectious disease processes may aid countermeasure development and lead to an improved understanding of pathogenesis. However, few studies have identified biomarkers for monitoring infections using in vivo imaging. Previously, we demonstrated that positron emission tomography/computed tomography (PET/CT) imaging with [18F]-fluorodeoxyglucose (FDG) can monitor monkeypox disease progression in vivo in nonhuman primates (NHPs). In this study, we investigated [18F]-FDG-PET/CT imaging of immune processes in lymphoid tissues to identify patterns of inflammation in the monkepox NHP model and to determine the value of [18F]-FDG-PET/CT as a biomarker for disease and treatment outcomes. Quantitative analysis of [18F]-FDG-PET/CT images revealed differences between moribund and surviving animals at two sites vital to the immune response to viral infections, bone marrow and lymph nodes (LNs). Moribund NHPs demonstrated increased [18F]-FDG uptake in bone marrow 4 days postinfection compared to surviving NHPs. In surviving, treated NHPs, increase in LN volume correlated with [18F]-FDG uptake and peaked 10 days postinfection, while minimal lymphadenopathy and higher glycolytic activity were observed in moribund NHPs early in infection. Imaging data were supported by standard virology, pathology, and immunology findings. Even with the limited number of subjects, imaging was able to differentiate the difference between disease outcomes, warranting additional studies to demonstrate whether [18F]-FDG-PET/CT can identify other, subtler effects. Visualizing altered metabolic activity at sites involved in the immune response by [18F]-FDG-PET/CT imaging is a powerful tool for identifying key disease-specific time points and locations that are most relevant for pathogenesis and treatment.IMPORTANCE Positron emission tomography and computed tomography (PET/CT) imaging is a universal tool in oncology and neuroscience. The application of this technology to infectious diseases is far less developed. We used PET/CT imaging with [18F]-labeled fluorodeoxyglucose ([18F]-FDG) in monkeys after monkeypox virus exposure to monitor the immune response in lymphoid tissues. In lymph nodes of surviving monkeys, changes in [18F]-FDG uptake positively correlated with enlargement of the lymph nodes and peaked on day 10 postinfection. In contrast, the bone marrow and lymph nodes of nonsurvivors showed increased [18F]-FDG uptake by day 4 postinfection with minimal lymph node enlargement, indicating that elevated cell metabolic activity early after infection is predictive of disease outcome. [18F]-FDG-PET/CT imaging can provide real-time snapshots of metabolic activity changes in response to viral infections and identify key time points and locations most relevant for monitoring the development of pathogenesis and for potential treatment to be effective.

Core-Shell-Shell NaYbF4:Tm@CaF2@NaDyF4 Nanocomposites for Upconversion/T2-Weighted MRI/Computed Tomography Lymphatic Imaging

To circumvent the defects of different bioimaging techniques, the development of multifunctional probes for multimodality bioimaging is required. In the present study, a lanthanide-based core-shell-shell nanocomposite NaYbF4:Tm@CaF2@NaDyF4 composed of an ∼9.5 nm NaYbF4:Tm nanocrystal as the core, ∼2 nm CaF2 as the middle layer, and 1-2 nm NaDyF4 as the outermost shell was designed and synthesized. Following surface modification with the ligand, citrate acid, this nanocomposite was hydrophilic, emitted intense upconversion luminescence (UCL), and displayed a high X-ray computed tomography (CT) value of ∼490 Hounsfield units (HU) and excellent r2 relaxivity of 41.1 mM(-1) s(-1). These results confirmed that the introduction of a middle CaF2 layer was necessary as a barrier to reduce cross-relaxation and the surface quenching effect, thus enhancing the upconversion emission of Tm(3+). This citrate-modified NaYbF4:Tm@CaF2@NaDyF4 nanocomposite was used as a multifunctional contrast agent for trimodal lymphatic bioimaging with T2-weighted magnetic resonance imaging (MRI), CT, and UCL imaging. The concept of fabricating a core-multishell nanostructure and the introduction of a Dy(3+)-based host as an outer layer is a useful strategy and can be used to develop a novel multifunctional nanoprobe for multimodality bioimaging.

Clinical and radiological feature of lymphoepithelial cyst of the pancreas

A lymphoepithelial cyst (LEC) of the pancreas is a rare benign lesion. Because patients with LEC of the pancreas have a good prognosis, it is important that these lesions are accurately differentiated from other more aggressive pancreatic neoplasms for an appropriate treatment strategy. Previous studies have reported that a definitive diagnosis of LEC often cannot be obtained based solely on the findings of preoperative imaging (e.g., Computed tomography or Magnetic resonance imaging). In this study, we reviewed four cases of pancreatic LECs to investigate the feature of LECs. We reviewed these cases with regard to symptoms, imaging findings, surgical procedures, and other clinical factors. We found that LEC was associated with unique characteristics on imaging findings. A preoperative diagnosis of LEC may be possible by comprehensively evaluating its clinical and imaging findings.

Jugular lymphatic sacs in first-trimester fetuses with normal nuchal translucency

OBJECTIVE

To assess the ultrasonographic appearance of the jugular lymphatic sacs (JLS) in first-trimester fetuses with a normal nuchal translucency (NT).

METHODS

Seventy-five fetuses with a normal NT thickness (< 95(th) percentile) were examined weekly between 11 and 17 weeks of gestation. After measurement of the NT thickness, the neck region was examined using both transvaginal and transabdominal ultrasonography for the presence of JLS. If present, their dimensions were measured in three directions and the volume was calculated using the formula for a spheroid. Data were analyzed using multilevel analysis.

RESULTS

Seventy-five fetuses were evaluated and a total of 243 ultrasound examinations of the neck region were performed. In 25 (33%) of the 75 fetuses, the JLS could be observed once or more than once. In 19 fetuses JLS were visualized once, in five fetuses twice and in one fetus three times. In total, the JLS were visualized 32 times (n = 15 bilaterally, n = 15 only the left JLS and n = 2 only the right JLS). Relatively greater NT thickness was associated with a higher probability of the presence of JLS, although this was not statistically significant (NT < 1 mm, probability 0.07; NT 1-2 mm, probability 0.15, P = 0.10; NT > 2 mm, probability 0.20, P = 0.08). Gestational age was predictive for the presence of JLS, with the highest probability between 13 and 15 weeks of gestation (P < 0.01). No relationship was found between gestational age and the volumes of the left and right JLS.

CONCLUSION

The JLS can be visualized on ultrasound examination in a significant proportion of fetuses with normal NT, most often between 13 and 15 weeks of gestation, and this does not seem to be associated with any abnormality in these fetuses.

Lymphoepithelial cyst of the pancreas tail. Case report and review of the literature

CONTEXT

Lymphoepithelial cyst of the pancreas is a lesion that comprises a stratified squamous epithelial lining atop dense lymphoid tissue.

CASE REPORT

We report our case of a 56-year-old man presented with recurrent abdominal pain. A CT scan showed a cystic lesion between the spleen and the pancreas. A distal pancreatectomy with splenectomy was performed. All pancreatic tissue was submitted for histologic examination. The patient recovered on the ward. On postoperative day two, the patient started eating an advanced diet. He was discharged on postoperative day four. The cyst is comprised of benign stratified squamous epithelium atop dense lymphoid tissue, which was consistent with cyst.

CONCLUSION

Good preoperative radiological anatomical mapping, good communication and good cooperation between the pathologist and the surgeon are essential to resect the lymphoepithelial cyst and exclude malignancy.

Blunt abdominal trauma: current imaging techniques and CT findings in patients with solid organ, bowel, and mesenteric injury

Imaging plays a critical role in the evaluation of patients with blunt abdominal trauma. In most institutions, computed tomography (CT) is the modality of choice when evaluating such patients. The purpose of this review is to highlight current techniques in trauma imaging and to review CT findings associated with solid organ, bowel, mesenteric, and diaphragmatic injury. In particular, emphasis is placed on the use of multidetector CT technology (MDCT), especially 64-row detector CT. The role of various techniques, including the use of oral and intravenous contrast, as well as the potential benefit of delayed imaging, is discussed.

The lymphatic territories of the upper limb: anatomical study and clinical implications

BACKGROUND

Current understanding of the pattern of lymph channels is largely dependent on the anatomical studies of Sappey performed in the nineteenth century, when mercury was injected into human cadavers and the lymphatics were dissected. These studies have not been repeated because the use of mercury is now prohibited as a result of its toxicity. The aim of this study was to reappraise the gross lymphatic anatomy and lymph node connections using a radiologic technique. A period of 3 years was required for development of a new method.

METHODS

The definitive technique used hydrogen peroxide to identify lymphatic vessels and to inflate them. The individual channels were injected with a radiopaque lead oxide mixture and recorded on x-ray film. Each channel was dissected meticulously under the surgical microscope and its course examined in relation to the regional lymph nodes. This method was then applied to 14 human cadaver upper limbs obtained from 10 different cadavers.

RESULTS

The authors found that the superficial lymphatic vessels course within the subcutaneous fat in close proximity to the main subcutaneous veins. Communication between the superficial and the deep lymphatic systems was not identified in these studies.

CONCLUSIONS

Most lymph vessels were seen to flow into one main (sentry) lymph node in the axillary region; however, some of the lymph vessels ran along the posterior forearm, bypassing the "sentry" node to reach other smaller nodes.

Diffuse Lung Cysts in Lymphoid Interstitial Pneumonia

Lymphoid interstitial pneumonia is part of a spectrum of pulmonary lymphoproliferative disorders that range from benign, small, and airway-centered cellular infiltrates (follicular bronchiolitis, nodular lymphoid hyperplasia) to low-grade malignant lymphoma. Most of the cases occur in patients with underlying autoimmune disease or immunodeficiency. The characteristic high-resolution computed tomography findings consist of diffuse ground-glass opacities, ill-defined centrilobular nodules, bronchovascular thickening, interlobular septal thickening, and scattered thin-walled cysts. The cysts may be seen in up to 80% of the patients and are typically few in number and measure less than 3 cm in diameter. This case illustrates extensive cysts as the predominant high-resolution computed tomography finding of idiopathic lymphoid interstitial pneumonia in a 64-year-old man who underwent unilateral lung transplant. Such extensive cystic disease and lung transplantation treatment has not been previously described.

Benign lymphoepithelial parotid lesions in vertically HIV-infected patients

Benign lymphoepithelial parotid lesions (BLL) are frequently reported in HIV-infected patients, although their clinical and prognostic significance in HIV infection has not been clearly defined. Ultrasonography (USG) has been shown to be a reliable method in monitoring the progression of such lesions. The purpose of this study was to describe the spectrum of sonographic and Doppler findings and to monitor any clinically evident physical change of parotid glands in a cohort of congenitally HIV-infected patients taking antiretroviral therapy. USG findings-based on their severity-have been grouped in three different patterns (0, 1, 2). Our cohort consisted of 51 patients with HIV in various Centers for Disease Control (CDC) stages and being given different antiretroviral protocols. The median USG follow-up was 36 months. The most frequent USG pattern was aspecific parotid gland enlargement (type 0, 45,1%). Patients with either lower CD4+ % (p < 0.20) and higher absolute and percent CD8+ cell count (p < 0.001 and p < 0.003) presented more frequently a type 2 USG pattern. None of them had any symptoms ascribed to "sicca syndrome" and only one patient developed non-Hodgkin's lymphoma during the follow-up, although his USG pattern at baseline was type 0. In summary, the spectrum of USG findings of BLL in vertically HIV-infected patients is broad. Because of the reported, although rare, possible malignant transformation of BLL in HIV-infected children, it is advisable to perform-even in asymptomatic patients-USG at least once per year or in concomitance with any physical modification of the parotid lesions.

Kinetics and dynamic evaluation of specific immunotherapy

Specific immunotherapy (SIT) is frequently used in the treatment of allergic diseases. However, the mechanisms by which SIT achieves clinical improvement remained unclear. We decided to study the in vivo kinetics of this therapy, using a nuclear medicine approach (leukocytes labelled with 99mTc-HMPAO) in patients on maintenance doses of specific immunotherapy with confirmed clinical efficacy.

MATERIAL AND METHODS

We studied 13 allergic patients grouped according to different treatment schedules: subcutaneous aqueous allergenic extract (3 latex and 2 hymenoptera venom), subcutaneous depot extract (2 house dust mite and 2 pollens), subcutaneous modified allergens (2 pollens), sublingual extract (2 house dust mites). The control group included two allergic patients submitted to subcutaneous injections of bacterial extract (1 patient--positive control), and aqueous solution (1 patient). At the same time that the therapeutic allergen was administered subcutaneously, the autologous labelled white cells were injected intravenously in a peripheral vein in the contralateral arm. A thoracic dynamic acquisition of 60 mins, 64x64 matrix, 2 frame/min, in anterior view was performed. Static acquisition for 256x256 matrix, during 5 mins each at 60, 90, 120, 180, 240, 300 and 360 mins after the administration of the radiolabelled leukocytes, in thoracic (anterior and posterior), and abdominal view were performed. During the examination, the local erythema was monitored. A similar procedure was undertaken for Sublingual administration of immunotherapy.

RESULTS

The inflammatory activity at the site of SIT injection (aqueous depot extract) started in the first hour and the increase was time related. For modified allergen extract and sublingual SIT the activity was present since the beginning of the administration. The ascendant lymphatic drainage, which was directed to the homolateral axillary region, to the lymphoid tissue of the upper mediastinum and to the anterior region of the neck began earlier. Thoracic focalisations were present for all the patients, whereas bowel focalisations were only observed for the subcutaneous route of administration. Sublingual SIT did not induce axillary or intestinal inflammatory focalisations, even though the patients had swallowed the allergenic extract. The uptake coefficient in individualized areas corrected to the uptake coefficient background was also studied.

CONCLUSIONS

For the subcutaneous route of administration, except for glutaraldehyde-modified allergen, the local inflammatory activity at the allergenic injection site was significantly higher in depth and was time dependent, maintaining activity even after complete disappearance of the erythema and/or wheal. These results express a prompt inflammatory involvement of the immune system with this allergenic therapy, which was unexpected until now. We also observed differences concerning allergic diseases, the type of allergenic extracts and routes of administration.

Lymphatic drainage of the skin

A successful sentinel lymph node biopsy (SLNB) in melanoma patients requires an accurate map of the pattern of lymphatic drainage from the primary site. Lymphoscintigraphy (LS) can provide such a map. LS needs an understanding of lymphatic physiology, an appropriate small-particle radiocolloid, high-resolution collimators, and imaging protocols that detect all sentinel nodes (SNs). Patterns of lymphatic drainage from the skin are not clinically predictable. Unexpected drainage has been found from the skin of the back to SNs in the triangular intermuscular space (TIS) and the paraaortic, paravertebral, and retroperitoneal areas. It can also occur from the base of the neck up to nodes in the occipital or upper cervical areas or from the scalp down to nodes at the neck base, bypassing many node groups. Upper limb drainage can be to SNs above the axilla. Interval nodes not uncommonly can be SNs, especially on the trunk. Lymphatic drainage may involve SNs in multiple nodal fields, and drainage across the midline of the body is quite common. Because micrometastatic disease can be present in any SN regardless of its location, all true SNs must be biopsied. LS is an important first step to ensure this goal is achieved.

A pilot study of the use of 2-[18F]-fluoro-2-deoxy-D-glucose-positron emission tomography to assess the distribution of activated lymphocytes in patients with systemic lupus erythematosus

OBJECTIVE

The 2-[(18)F]-fluoro-2-deoxy-D-glucose-positron emission tomography (FDG-PET) technique provides information on uptake and metabolism of glucose in various tissues. Compared with resting cells, activated lymphocytes take up radioactively labeled glucose analog at a higher rate, which makes it possible to identify lymphoid organs with higher concentrations of activated lymphocytes. This study was undertaken to compare the pattern of PET images and quantitative FDG uptake in lymphoid organs of patients with active systemic lupus erythematosus (SLE) versus patients with inactive SLE and to correlate these findings with peripheral blood lymphocyte phenotypes.

METHODS

Ten patients with active SLE and 9 patients with inactive SLE were studied. FDG-PET images were obtained from the inguinal region to above the ear, starting at 60 minutes after injection of FDG. Standardized uptake values using lean body mass were determined over areas of interest.

RESULTS

Both patients with active lupus and those with inactive lupus had increased FDG uptake in lymph nodes when compared with healthy volunteers, and there was no statistically significant difference between the 2 groups of lupus patients. Thymic uptake was demonstrated in 5 of 10 patients with active lupus compared with 0 of 9 patients with inactive disease. Three of the 5 patients with active SLE who were over 29 years of age had thymic uptake. Of the activation markers tested, only the CD3/CD71 population of cells was significantly different between the patient groups, with an increased percentage in the active disease group (P = 0.0247).

CONCLUSION

Increased FDG uptake in lymph nodes of both patients with active SLE and patients with inactive SLE suggests that metabolic, and probably immunologic, activity is enhanced not only in active, but also in clinically quiescent, disease. The increased thymic uptake observed only in patients with active disease suggests that the thymus plays an important role during periods of disease activity.

Technetium-99m scintigraphy to visualize T-cell homing in vivo: a preclinical study

The knowledge of lymphocyte distribution is very usefulness in monitoring therapeutic treatments. We present here a method employed in clinical practice, the scintigraphy, to study in the rat the physiologic lymphocyte traffic. Rat T cells labeled with 99mTc were injected in syngeneic animals, and their fate was studied by serial scintigraphic scanning. Sorted naïve CD4+ CD45RC(bright) T cells homed to lymphoid organs and accumulated in spleen. CD4+ CD45RC(dim) memory lymphocytes first reached the liver and the lungs and recirculated. The results obtained by using the scintigraphic method to in vivo study the lymphocyte homing in rats are comparable to those obtained with previously used experimental methods. We consider the scintigraphic method a useful tool to in vivo track lymphocytes and to address therapeutic treatment in men.

Follicular cholangitis: another cause of benign biliary stricture

The case of a 57-year-old woman with a benign biliary stricture is described. Radiological examinations showed granularly elevated lesions in the common hepatic duct and severe stenosis at the hepatic hilum. Under a tentative diagnosis of hepatic hilar bile duct cancer, the patient underwent extended right hepatectomy with bile duct resection. However, pathological and immunohistochemical studies revealed a benign stricture with remarkable formation of lymph follicles with germinal centers, which could be termed "follicular cholangitis". This is the first case report of this uncommon presentation of inflammatory changes of the bile duct. Its etiology was unknown, and more investigation is encouraged to clarify its relationship to systemic disorders and malignancies. As difficulty remains in discriminating between benign and malignant strictures by nonsurgical modalities at present, surgical resection without complications provides a feasible approach to such a benign lesion.

[Bronchial-associated lymphoid tissue lymphoma]

Two cases of non-Hodgkin's endobronchial or bronchial-associated lymphoid tissue lymphoma are reported; such cases are either extremely rare or underestimated. We emphasize the need to perform endoscopic examination in patients with lymphoma and clinical findings that suggest bronchial disease.

Features of 'CD4-exploders', HIV-positive patients with an optimal immune reconstitution after potent antiretroviral therapy

OBJECTIVE

To identify crucial immunological characteristics of a group of patients, defined 'CD4-exploders', who were able to fully reconstitute their immune system after receiving highly active antiretroviral therapy (HAART).

PATIENTS

Among a population of 540 HIV-positive patients treated with HAART, six individuals were identified who experienced a nadir of less than 85 x 106 CD4+ cells/l, had major opportunistic infections (four out of six), started HAART in 1996 or 1997, and showed a rapid and relevant CD4+ lymphocyte increase (mainly due to virgin cells), in some cases regardless of virological control.

METHODS

Enzyme-linked immunosorbent assay for the determination of interleukin (IL)-7 plasma levels; flow cytometry to analyse surface antigens and CD127 (IL-7 receptor alpha-chain) expression; quantitative-competitive (QC) PCR for detecting cells containing T-cell receptor rearrangement excision circles (TREC); chest-computed tomography (CT) to analyse thymus volume and content.

RESULTS

In 'CD4-exploders', high levels of TREC+ lymphocytes were found among CD4+ T cells, which also contained a high percentage of naive cells. However, CT revealed a dramatic depletion of intrathymic lymphoid tissue. Plasma levels of IL-7 were significantly high. Most CD4+ and CD8+ T lymphocytes expressed CD127, whose level was similar to that of healthy donors. CD127 expression on CD8+ lymphocytes was markedly higher than in HIV-positive individuals treated with the same therapy or in patients with AIDS.

CONCLUSION

In 'CD4-exploders', HAART-induced reconstitution of the T-cell compartment is independent from thymus volume, and is favoured by the upregulation of the IL-7/IL-7 receptor system.

Bronchus-associated lymphoid tissue (BALT) lymphoma of the lung showing mosaic pattern of inhomogeneous attenuation on thin-section CT: a case report

The authors present a case of histologically proven bronchus-associated lymphoid tissue (BALT) lymphoma of the lung in a patient with primary Sjögren's syndrome that manifested on thin-section CT scan as a mosaic pattern of inhomogeneous attenuation due to mixed small airway and infiltrative abnormalities

Management of benign lymphoepithelial lesions of the parotid gland in human immunodeficiency virus-positive patients

The diagnosis and radiotherapeutic treatment of these HIV-associated benign lymphoepithelial lesions in the parotid gland are discussed. As an example of these lesions, a case is presented involving a 43-year-old HIV-infected man with a 2-year history of enlargements in both parotid glands. After evaluation by computer tomography and cytology, the diagnosis of benign lymphoepithelial lesions was made. Treatment by low-dose radiotherapy (15 Gy) caused regression of both lesions. The lesion on the left regressed completely, but the one on the right side responded only partially. A second course of high-dose radiotherapy (24 Gy) to the right lesion caused regression to a cosmetically acceptable size.

Lymphoepithelial cysts of the pancreas: demonstration of lipid component using CT and MRI

We present two cases of surgically proven lymphoepithelial cyst (LEC) of the pancreas that had a lipid component visualized by CT and MRI. Identification of this component in a pancreatic cystic lesion is a key to favor the diagnosis of LEC or splenic epidermoid cyst over other cystic lesions when the lesion is noted in an elderly patient.

[Bronchial casts associated with pulmonary lymphatic anomalies]

We report a case of a patient who presented with bronchial moulds. The classic causes, particularly bronchopulmonary aspergillosis could not be found. The pulmonary radiology and CT of thorax revealed an alveolar syndrome. Lymphography and lymphoscintigraphy showed evidence of lymphatic anomalies including the non-visualisation of the thoracic canal. In the absence of evidence for other diseases, we would suggest that these anomalies were responsible for the symptomatology.

Multilocular thymic cysts in children with human immunodeficiency virus infection: clinical and pathologic aspects

BACKGROUND

Children with human immunodeficiency virus (HIV) infection have an increased susceptibility to severe and unusual infections, malignancies, and disorders characterized by abnormal lymphoproliferation (e.g., lymphoid interstitial pneumonitis). We report a novel disease entity associated with pediatric HIV infection that is characterized by massive enlargement of the thymus as a result of lymphoid hyperplasia and multicystic changes.

METHODS

Eight patients with HIV infection and cystic enlargement of the thymus are subject of this report. The status of their HIV disease and its clinical and radiologic manifestations at the time of diagnosis of the mediastinal mass are described. Tissue specimens were obtained from six patients and examined by microscopy and immunohistochemistry. The specimens were also evaluated for the evidence of HIV and Epstein-Barr virus by in situ hybridization.

RESULTS

Patients were between 2.1 and 12.1 years of age, with CD4+ cell counts between 102 and 733 cells/mm3. In all eight cases an anterior mediastinal mass was discovered incidentally on radiography of the chest, and computed tomography of the chest revealed a multicystic appearance. Histologic examination demonstrated distortion of the thymic architecture by focal cystic changes, lymphoid follicular hyperplasia, diffuse plasmacytosis, and multinucleated giant cells. In situ hybridization revealed HIV particles on the surface of follicular dendritic cells. Further, results of in situ hybridization for EBV were positive in lymphoid cells from biopsy samples of four patients. The patients were followed between 8 months and 4.8 years. In five patients the mass either decreased in size or resolved completely.

CONCLUSIONS

We describe a series of children with HIV infection and multilocular thymic cysts. We hypothesize that aberrant immunoregulation in these HIV-infected children leads to follicular hyperplasia and multicystic changes in the thymus, causing massive enlargement. EBV infection might also contribute to the pathogenesis of this process. Because none of our patients had symptoms from the mass, and there was no evidence of malignancy in the examined biopsy samples, it seems prudent to manage such children with careful follow-up examinations.

Clinical and radiological presentation of 95 orbital lymphoid tumors

BACKGROUND

Although most orbital lymphoid tumors are characterized by a slow, painless onset and a mass that molds to orbital structures, different presentations may occur. Intensity on T2-weighted MRI is a possible means for differentiating lymphoid tumors (hyperintense) from pseudotumors (hypointense). In addition, it is generally assumed that 75% of orbital lymphomas are at stage I on presentation.

METHODS

The clinical, CT, and MRI presentation of 95 primary and secondary orbital lymphoid tumors (63 non-Hodgkin lymphomas and 32 lymphoid hyperplasias) and their histological grade and staging were reviewed. Immunohistochemistry and PCR were used to determine clonality.

RESULTS

No significant differences were found between non-Hodgkin lymphomas and lymphoid hyperplasias, except for the mean age of the patients (6.3 years older in non-Hodgkin lymphomas). In both groups the most common presentation was a mass with an indolent course; visual impairment was seen in 13%, conjunctival redness in 25%, pain in 12%, and acute orbital inflammation in 15% of the patients. In most cases, the CT showed one or more lobulated or rounded masses, molding to adjacent structures, or a wedge-shaped enlargement of the lacrimal gland. Intramuscular lymphomas were rare and always associated with extramuscular masses. On T2-weighted MRI, only 35% of lymphoid tumors were hyperintense. Only 49% of lymphomas were at stage I on presentation.

CONCLUSION

An inflammatory presentation is not uncommon in orbital lymphoid tumors. Shape, molding and multiple masses can help radiological diagnosis, whereas MRI T2 intensity is unreliable. Accurate staging can disclose systemic disease in more than 50% of cases of non-Hodgkin lymphoma.

Whole body positron emission tomography imaging of simian immunodeficiency virus-infected rhesus macaques

Pathogenesis of simian immunodeficiency virus (SIV) infection in rhesus macaques begins with acute viremia and then progresses to a distributed infection in the solid lymphoid tissues, which is followed by a process of cellular destruction leading to terminal disease and death. Blood and tissue specimens show the progress of infection at the cellular level but do not reveal the pattern of infection and host responses occurring throughout the body. The purpose of this investigation was to determine whether positron emission tomography (PET) imaging with intravenous 2-18F-2-deoxyglucose (FDG) could identify activated lymphoid tissues in a living animal and whether this pattern would reflect the extent of SIV infection. PET images from SIV-infected animals were distinguishable from uninfected controls and revealed a pattern consistent with widespread lymphoid tissue activation. Significant FDG accumulation in colon along with mesenteric and ileocaecal lymph nodes was found in SIV infection, especially during terminal disease stages. Areas of elevated FDG uptake in the PET images were correlated with productive SIV infection using in situ hybridization as a test for virus replication. PET-FDG images of SIV-infected animals correlated sites of virus replication with high FDG accumulation. These data show that the method can be used to evaluate the distribution and activity of infected tissues in a living animal without biopsy. Fewer tissues had high FDG uptake in terminal animals than midstage animals, and both were clearly distinguishable from uninfected animal scans.

Local and systemic effects of water-soluble contrast media and barium in rats with chronic small bowel obstruction

RATIONALE AND OBJECTIVES

The local effects on the small intestine and systemic changes produced by different contrast media in small bowel obstruction, with time courses of 4 days, were evaluated.

MATERIALS AND METHODS

Four groups, each with 10 normal rats and another four groups (also each with 10 rats) that had ligation of the terminal ileum (obstructed rats) for 4 days were given 3 mL of barium, meglumine sodium diatrizoate, iohexol, or saline (control animals). Radiographs were taken immediately, 1 and 4 hours after administration of contrast media. Immediately before sacrifice, blood samples were taken to determine the hematocrit (Hct), hemoglobin (Hb), white blood cell count (WBC), red blood cell count (RBC), and serum sodium, and potassium and chloride concentrations. Specimens of small bowel were taken for histologic and morphometric analysis.

RESULTS

In obstructed rats, the image quality with iohexol improved on final radiographs despite being diluted in the great intestinal contents. There was an improvement in the serum electrolyte concentrations in the obstructed animals that were given any one of the contrast media, the best improvement being in the iohexol groups. A shortening of the length of epithelial cells when any one of the contrast media was administered was observed, as was an increase in the lymphatic space area in the diatrizoate group in normal rats. In the bowel proximal to the obstruction, the lymphatic space area was increased in the diatrizoate group and the size of the epithelial cells was higher in the diatrizoate and iohexol groups compared to the barium and saline groups.

CONCLUSION

Our results suggest that iohexol offers good radiologic efficacy and excellent systemic and local tolerance in small bowel obstruction.

Bronchus associated lymphoid tissue (BALT) in human lung: its distribution in smokers and non-smokers

BACKGROUND

Bronchus associated lymphoid tissue (BALT) is a normal component of the lung's immune system in many animals and may be analogous to gut associated lymphoid tissue (GALT). This study aimed at assessing the nature and extent of BALT in human lung and determining whether its expression is induced within the human airway in response to smoking.

METHODS

Paraffin embedded, formalin fixed full thickness bronchial wall sections were examined from 31 whole lung specimens derived from both smokers and non-smokers. Samples were taken from throughout the bronchial tree to include main stem bronchi, lobar bronchi and segmental bronchi, as well as first to third generation carinae. Standard 4 microns step sections were stained by haematoxylin and eosin and immunocytochemical methods to show foci of BALT.

RESULTS

Examination of 256 airway sites detected 46 foci of BALT. These differed from those described in other mammals in being distributed throughout the bronchial tree, in being found in relation to bronchial glandular epithelium as well as luminal bronchial epithelium, and in lacking any accompanying M cells. Analysis by smoking status showed that the expression of BALT was significantly more common in smokers than non-smokers (82% (14/17) v 14% (2/14) respectively).

CONCLUSIONS

The findings support the view that BALT in humans is an integral feature in a comparatively small proportion of lungs from non-smokers while being significantly more prominent in lungs from smokers. The tissue shows several important differences from that described in other mammals.

Joint uptake and body distribution of a technetium-99m-labeled anti-rat-CD4 monoclonal antibody in rat adjuvant arthritis

Joint uptake and body distribution of a 99mTc-labeled monoclonal antibody (Mab) to the rat CD4 molecule (W3/25; IgG1) were investigated after intravenous injection in normal rats and in animals with experimentally induced adjuvant arthritis. An isotype-matched Mab with irrelevant specificity (anti-human carcino-embryonic-antigen) was used as control. A 4 hr sequential gamma-camera imaging revealed that both anti-CD4 and control Mab accumulated to a higher degree in arthritic than in normal ankle joints; the accumulation was comparable for the two Mabs. In contrast to the inflamed joints, a specific accumulation of the anti-CD4 Mab was found in organs rich in CD4-positive cells, i.e. spleen, bone marrow and lymph nodes, as assessed by direct well counter measurements 16 hr after injection. The control Mab displayed no preferential organ accumulation in either normal or diseased animals. These results indicate that a specific accumulation of anti-CD4 Mabs occurs in CD4-positive-cell-rich tissues in both normal and diseased animals and that immunoglobulins accumulate preferentially in inflamed joints regardless of their antibody specificity.

Lymphocyte targeted ricin as a potential therapy for lymphoid malignancy. I. Targeting efficiency

Lymphocytes were studied as vehicles to target the plant toxin ricin, to lymphoid tissue in rats. Ricin-loaded thoracic duct lymphocyte (TDL) migrated normally into lymph nodes (LN) at 0.5 h, but this process was arrested by 3 h after injection. Ricin was successfully targeted to lymphoid tissue as evidenced by a 4-fold increase in ricin-associated radioactivity in LN, a 10-fold increase in the Peyers patches, a doubling in the spleen and a 35% reduction of radioactivity in the liver compared with free ricin. Nevertheless this represented a considerable shortfall in the expected targeting efficiency. The main problem was found to be high in vivo elution of ricin from TDL (70% within 0.5 h of i.v injection). This and other aspects relevant to maximising targeting efficiency are discussed.

Migration of 99mTc-labelled syngeneic lymphocytes in the rat. Biological and theoretical models predict radiation damage and poor scintigraphic detectability

The possibility of obtaining useful scintigrams of secondary lymphoid organs after infusion of syngeneic lymphocytes labelled with technetium-99m (99mTc) was explored in a rat model. Thoracic duct lymphocyte (TDL) accumulation in various organs was measured with both 99mTc and 51Cr labelled cells, the latter processed with a method that has been shown not to damage lymphocytes. 99mTc labelled TDL did not localize properly in the lymph nodes and spleen. We could not visualize lymph nodes in scintigrams, neither could we demonstrate any difference between normal and hyperplastic spleens. Our conclusion is that radiation from the 99mTc label readily influences lymphocyte migration so that useful scintigraphy in rats and other small experimental animals becomes impossible. This was supported by results from culture experiments with 99mTc labelled, radiosensitive mouse haemopoietic progenitor cells. Theoretical considerations, including the calculations of lymphocyte self-irradiation and signal/noise ratios during scintigraphy of rat tissues, supported our conclusion that scintigraphy in small animals, to disclose the physiological migration of lymphocytes, may be impossible with the present sensitivity of gamma cameras.

Lymphoid follicular hyperplasia in excluded colonic segments: a radiologic sign of diversion colitis

Double-contrast barium enema (DCBE) studies showed lymphoid follicular hyperplasia (LFH) in excluded colonic segments after colostomy in 12 of 40 patients. In most patients with LFH, more than 80% of the excluded colon was affected. In eight patients, regression of LFH was demonstrated with DCBE studies after reanastomosis. This work suggests that LFH is the most common DCBE study finding in diversion colitis.

Colonic lymphoid follicles associated with colonic neoplasms

In 3,399 patients more than 40 years of age undergoing air-contrast enema examinations a prospective evaluation was done for the presence of colonic lymphoid follicles. In 3,315 patients there was no evidence of lymphoid follicles. Colonic neoplasms were diagnosed in 8.47% of these individuals. Eighty-four patients were found to have radiographically identifiable follicles. Fifty-eight of these 84 patients (69%) with lymphoid follicles had a synchronous (n = 19) or previous (n = 14) colonic neoplasm or a synchronous (n = 24) or previous (n = 1) colonic polyp. There were no consistent clinical or radiographic features that distinguished the patients with and without a neoplastic association. However, 90% of men with lymphoid follicles had associated neoplasms, whereas only 58% of women did. Because of the frequent association, detection of colonic lymphoid follicles in patients in this age group should lead to a vigorous search for subtle colonic neoplasms that may not be apparent because of technical limitations of the study.

Effect of pretransplant graft irradiation on canine intestinal transplantation

This study was done to define the tolerance of ex vivo administered irradiation to intestinal allograft and to assess the effect of irradiation on the incidence and severity of rejection and graft versus host disease after intestinal transplantation in dogs. Excessive intestinal damage was produced by 2,500 rads, but 750 and 1,500 rads produced no detectable acute or chronic damage in dogs observed from 100 days to two years. Using cyclosporine for postoperative immunosuppression, 1,500 rads reduced the incidence of acute (p = 0.05) and chronic rejection (p = 0.08), yet did not impair intestinal absorption of cyclosporine. The greatest improvement in survival occurred with 750 rads (p = 0.02). Histologic evidence of graft versus host disease appeared in the native small intestine in two of four long term surviving dogs receiving a nonirradiated graft but in none of the dogs receiving irradiated grafts. Irradiation of the graft may be a promising adjunct in the search for a clinically applicable method of intestinal transplantation.

Corticosteroid treatment for pulmonary lymphoid hyperplasia in children with the acquired immune deficiency syndrome

Five children with positive serology for human immunodeficiency virus (HIV) infection by enzyme-linked immunosorbent assay and Western blot were followed for chronic pulmonary disease. Lung biopsies were performed in all patients, and confirmed the diagnosis of pulmonary lymphoid hyperplasia. All children demonstrated progressive hypoxia and increasing alveolar capillary oxygen gradients over at least 1 year of follow-up. All children were on periodic intravenous gamma globulin treatment for a B-cell defect prior to the initiation of corticosteroid therapy. Prednisone was initially given at a dose of 2 mg/kg daily and was subsequently tapered to an alternate day regimen. All children showed improvement in oxygenation. No deterioration in immune function was noted, and there was no increase in bacterial infection. This study indicates that corticosteroids can successfully reverse the severe hypoxia that may result from pulmonary lymphoid hyperplasia in pediatric AIDS patients.

Nasopharyngeal lymphoid hyperplasia following treatment of patients with Hodgkin's disease

Nasopharyngeal tomography was performed in 64 patients following treatment of Hodgkin's disease. Symmetric soft tissue mass involving roof and lateral walls of the nasopharynx was revealed in 33 cases, of which 24 underwent biopsies from the nasopharynx. Histology of biopsy specimens detected characteristic lymphoid hyperplasia. Its frequency was found to be influenced by the mode of previous treatment. Its occurrence was more frequent amongst those having received total nodal irradiation (TNI) as to those with extended fields irradiation (EFI), the difference proved to be statistically significant. This finding supports our hypothesis that nasopharyngeal lymphoid hyperplasia is a compensatory mechanism evoked by damage of lymphoid tissue due to previous therapy. Nasopharyngeal biopsy or a close follow-up is proposed, depending on the shape of nasopharyngeal mass and the condition of cervical lymph node area.

Primary lymphoma of Waldeyer's ring. Clinicopathologic study of 68 cases

The clinical and pathologic findings were studied in 68 patients with primary lymphoma of Waldeyer's ring (WR). The initial sites included: tonsil (51%; 9% bilateral), nasopharynx (35%), base of tongue (9%), and multiple areas (4%). The mean age was 58 years, with a male to female ratio of 1.1:1.0. Tonsillar and base of tongue lesions presented with sore throat and dysphagia, whereas nasopharyngeal lymphomas most commonly presented with nasal, auditory, and cranial nerve sympatomatology. A neck mass was the sole presenting symptom in 12% of patients. Work-up showed 42% Stage I, 47% Stage II, 4% Stage III, and 7% Stage IV. All were non-Hodgkin's lymphomas. Diffuse architecture predominated (71%) and 70% had a histiocytic or large cell morphology (diffuse histiocytic 51%, nodular histiocytic 19%). The National Cancer Institute (NCI) Working Formulation grades were 13% low, 81% intermediate, and 6% high. In difficult cases, detection of monoclonal immunoglobulin, absence of keratin staining, and lack of epithelial features by electron microscopy were useful adjuncts aiding in diagnosis. Following complete remission, 28 patients relapsed, 75% of these within 2 years (median, 10 months). Thirty-seven (54%) patients died with disease (median survival, 27 months). Of these, 89% had disseminated lymphoma. Local-regional disease was the direct cause of death in 13%. Recurrence or persistence of disease in WR occurred in 9% of cases, most with initial clinical evidence of soft tissue extension. Stage I patients had a significantly better median survival (67 months) than Stage II patients (20 months) (P = 0.03). Prognostically favorable histologic parameters included lower NCI Working Formulation grade and follicular architecture. Ten patients (15%) developed extranodal disease, eight involving the gastrointestinal (GI) tract, and all died within 1 year of its occurrence. The findings indicate that stage and certain histologic parameters are important prognostic factors in WR lymphoma. The study confirms the association of primary WR lymphoma with other extranodal disease, particularly involving the GI tract, and emphasizes the poor prognosis of patients in whom this occurs.

Diffuse lymphoid follicles of the colon associated with colonic carcinoma

In four patients aged 59-75 years, colonic carcinoma was associated with diffuse lymphoid follicles in the colon. In one case, the prominence and distribution of the lymphoid follicles corresponded to the progression and regression of the tumor bulk. It is extremely unusual to demonstrate lymphoid follicles, particularly diffuse, on barium enema in patients in this age range. The colonic carcinomas and lymphoid follicles are directly related, possibly representing an immune response.

Total lymphoid irradiation in the Wistar rat: technique and dosimetry

The technical and dosimetric aspects of total lymphoid irradiation (TLI) in the Wistar rat were evaluated as part of a set-up to develop a new model for tumor xenotransplantation. Information obtained from anatomical dissections, radionuclide imaging of the spleen, lymphography and chromolymphography was used to standardize the localization of lymph nodes, thymus and spleen. A practical advantage was found in the simultaneous irradiation through two portals cut out in a lead plate. The two portals encompassed the lymphoid tissue above and below the diaphragm. A specially designed masonite phantom was used to measure the dose distribution in the simulated target volumes. Ionization chamber dosimetry, thermoluminescence dosimetry and film densitometry were used for measuring exposure and absorbed dose. Irradiation was performed with 250 kV X rays (HVL 3.1 mm Cu). The dose rate was regulated by adjusting the treatment distance. The dose inhomogeneity measured in the target volumes varied between 80-100%. The side scatter dose to non target tissues under the shielded area between the two portals ranged between 20-30%. The technique and dosimetry of total lymphoid irradiation in Wistar rats are now standardized and validated and pave the way for tumor xenotransplantation experiments.

Pancreatic Castleman disease simulating pancreatic carcinoma on computed tomography

A patient with a pancreatic body and tail mass caused by Castleman disease and visible on computed tomography is described. This entity simulated pancreatic carcinoma in this clinical setting. Theories of etiology of Castleman disease and differential diagnosis of pancreatic masses are discussed. Proper examination technique is stressed.

Bone marrow transplantation across major histocompatibility barriers in mice. II. T cell requirement for engraftment in total lymphoid irradiation-conditioned recipients

Studies were undertaken to examine the role of T lymphocytes in engraftment of bone marrow (BM) in animals conditioned with total lymphoid irradiation (TLI) prior to transplantation across major histocompatibility barriers. Donor BM (added as a source of lymphohematopoietic stem cells) and spleen cells (added as a source of graft-versus-host disease (GVHD)-causing cells) were pretreated in vitro with monoclonal anti-Thy-1.2 plus complement (C). T cell-depleted grafts were then give to allogeneic mice conditioned with 900 rad of single dose TLI plus cyclophosphamide (CY). These mice did not engraft. Even in the absence of added spleen cells, elimination of the small T cell population from donor BM grafts prevented engraftment compared with animals that received the same conditioning regimen and untreated donor cells. These control animals demonstrated uniform evidence of engraftment about 1 month after transplantation. Similar findings were reported when recipients were conditioned with fractionated 17 x 200-rad TLI. In TLI plus CY-conditional recipients, we have also observed that increasing the donation of treated bone marrow cells still did not result in significant engraftment. Furthermore, graft failure in mice receiving normal dosages of anti-Thy-1.2 plus C-treated donor cells was not a strain-restricted phenomenon. Moreover, removal of bone marrow T cells with monoclonal anti-Lyt-1 plus complement also resulted in graft failure in TLI-conditioned recipients. In contrast to TLI conditioning, when Thy-1.2 plus C-treated donor cells were given to recipients conditioned with total body irradiation (TBI), a high percentage of engraftment was demonstrated by an H-2 microcytotoxicity assay. Plausible mechanisms for there findings are discussed.