Anti-infective vaccination strategies in patients with hematologic malignancies or solid tumors-Guideline of the Infectious Diseases Working Party (AGIHO) of the German Society for Hematology and Medical Oncology (DGHO).

Infectious complications are a significant cause of morbidity and mortality in patients with malignancies specifically when receiving anticancer treatments. Prevention of infection through vaccines is an important aspect of clinical care of cancer patients. Immunocompromising effects of the underlying disease as well as of antineoplastic therapies need to be considered when devising vaccination strategies. This guideline provides clinical recommendations on vaccine use in cancer patients including autologous stem cell transplant recipients, while allogeneic stem cell transplantation is subject of a separate guideline. The document was prepared by the Infectious Diseases Working Party (AGIHO) of the German Society for Hematology and Medical Oncology (DGHO) by reviewing currently available data and applying evidence-based medicine criteria.

Influenza virus infections in patients with malignancies -- characteristics and outcome of the season 2014/15. A survey conducted by the Infectious Diseases Working Party (AGIHO) of the German Society of Haematology and Medical Oncology (DGHO).

Influenza virus infections (IVI) may pose a vital threat to immunocompromised patients such as those suffering from malignancies, but specific data on epidemiology and outcome in these patients are scarce. In this study, we collected data on patients with active cancer or with a history of cancer, presenting with documented IVI in eight centres in Germany. Two hundred and three patients were identified, suffering from haematological malignancies or solid tumours; 109 (54 %) patients had active malignant disease. Influenza A was detected in 155 (77 %) and Influenza B in 46 (23 %) of patients (genera not determined in two patients). Clinical symptoms were consistent with upper respiratory tract infection in 55/203 (27 %), influenza-like illness in 82/203 (40 %), and pneumonia in 67/203 (33 %). Anti-viral treatment with oseltamivir was received by 116/195 (59 %). Superinfections occurred in 37/203 (18 %), and admission on an intensive care unit was required in 26/203 (13 %). Seventeen patients (9 %) died. Independent risk factors for death were delayed diagnosis of IVI and bacterial or fungal superinfection, but not underlying malignancy or ongoing immunosuppression. In conclusion, patients with IVI show high rates of pneumonia and mortality. Early and rapid diagnosis is essential. The high rate of pneumonia and superinfections should be taken into account when managing IVI in these patients.

Diagnosis and antimicrobial therapy of lung infiltrates in febrile neutropenic patients (allogeneic SCT excluded): updated guidelines of the Infectious Diseases Working Party (AGIHO) of the German Society of Hematology and Medical Oncology (DGHO).

Up to 25% of patients with profound neutropenia lasting for >10 days develop lung infiltrates, which frequently do not respond to broad-spectrum antibacterial therapy. While a causative pathogen remains undetected in the majority of cases, Aspergillus spp., Pneumocystis jirovecii, multi-resistant Gram-negative pathogens, mycobacteria or respiratory viruses may be involved. In at-risk patients who have received trimethoprim-sulfamethoxazole (TMP/SMX) prophylaxis, filamentous fungal pathogens appear to be predominant, yet commonly not proven at the time of treatment initiation. Pathogens isolated from blood cultures, bronchoalveolar lavage (BAL) or respiratory secretions are not always relevant for the etiology of pulmonary infiltrates and should therefore be interpreted critically. Laboratory tests for detecting Aspergillus galactomannan, ß-D-glucan or DNA from blood, BAL or tissue samples may facilitate the diagnosis; however, most polymerase chain reaction assays are not yet standardized and validated. Apart from infectious agents, pulmonary side-effects from cytotoxic drugs, radiotherapy or pulmonary involvement by the underlying malignancy should be included into differential diagnosis and eventually be clarified by invasive diagnostic procedures. Pre-emptive treatment with mold-active systemic antifungal agents improves clinical outcome, while other microorganisms are preferably treated only when microbiologically documented. High-dose TMP/SMX is first choice for treatment of Pneumocystis pneumonia, while cytomegalovirus pneumonia is treated primarily with ganciclovir or foscarnet in most patients. In a considerable number of patients, clinical outcome may be favorable despite respiratory failure, so that intensive care should be unrestrictedly provided in patients whose prognosis is not desperate due to other reasons.

Treatment cost of invasive fungal disease (Ifd) in patients with acute myelogenous leukaemia (Aml) or myelodysplastic syndrome (Mds) in German hospitals.

Invasive fungal disease (IFD) causes increasing morbidity and mortality in haematological cancer patients. Reliable cost data for treating IFD in German hospitals is not available. Objective of the study was to determine the institutional cost of treating the IFD. Data were obtained by retrospective chart review in German hospitals. Patients had either newly diagnosed or relapsed acute myeloid leukaemia (AML) or myelodysplastic syndrome (MDS). Direct medical cost was calculated from hospital provider's perspective. A total of 108 patients were enrolled at 5 tertiary care hospitals, 36 IFD patients and 72 controls. The vast majority of IFD patients (74%) were diagnosed with invasive aspergillosis. On average, the hospital stay for IFD patients was 12 days longer than in control patients. All patients in the IFD group and 89% of patients in the control group received antifungal drugs. Mean direct costs per patient were €51,517 in the IFD group and €30,454 in the control group. Incremental costs of €21,063 were dominated by cost for antifungal drugs (36%), hospital stay (32%) and blood products (23%). From the perspective of hospitals in Germany the economic burden of IFD in patients with AML or MDS is substantial. Therefore, prevention of IFD is necessary with respect to both clinical and economic reasons.

Questionnaire to preselect patients with a high probability of primary ciliary dyskinesia.

BACKGROUND: As diagnostic methods for primary ciliary dyskinesia are not generally available, we tested whether clinical criteria allow to preselect patients with a high probability of this disease, who should be further investigated in a specialized centre. PATIENTS AND METHODS: In patients with chronic cough we compared parameters of the case history with the finding of a reduced ciliary beat frequency (CBF). Data sheets of 323 patients (133 females, 190 males) aged 1 week through 40 years (median age 4.5 years) were available for analysis. Of these patients 46 (14%) had a reduced CBF. RESULTS: In this group the following features were found significantly more frequently compared to patients with normal CBF: neonatal respiratory disorder (odds ratio (OR) 9.0; 95% confidence interval (95% CI) 3.2;25), situs inversus (OR 8.1; 95% CI 2.5;26), retention of airway secretions (OR 6.7; 95% CI 2.4;19), recurrent pneumonia (OR 4.1; 95% CI 1.8;9.5), bronchiectasis (OR 3.5; 95% CI 1.2;11), asthma with poor response to treatment (OR 2.4; 95% CI 1.1;5.3). At least one of these potential indicators was present in 91% of the patients with reduced CBF. CONCLUSIONS: In patients with chronic cough specific parameters of the case history indicate a high probability of a reduced ciliary beat frequency which is an indicator for primary ciliary dyskinesia. If none of these findings is present, a reduced CBF is highly unlikely.

Ultrasound and colour Doppler in infantile subglottic haemangioma.

BACKGROUND: Subglottic haemangioma causes progressive and life-threatening stridor, typically manifesting at age 2-3 months. Standard diagnosis is by laryngoscopy. Larynx sonography is rarely used but allows assessment of the presence and extension of a mass that impinges on the subglottic airway. The additional use of colour Doppler enables demonstration of the vascular nature of such masses. OBJECTIVE: To compare US and endoscopic findings in infants with subglottic haemangioma and to evaluate accuracy of US and colour Doppler imaging in this diagnosis. MATERIALS AND METHODS: We report eight infants with subglottic haemangioma seen in our institution over the last decade. They presented with laryngeal stridor and were all investigated with both US and endoscopy. Six infants underwent colour Doppler sonography. RESULTS: US and endoscopic findings showed excellent anatomical correlation in lateral subglottic haemangioma. Colour Doppler imaging was deemed helpful in four infants. CONCLUSION: Larynx sonography with complementary colour Doppler imaging was non-invasive and helpful in the diagnosis of subglottic haemangioma.

Infectious complications after allogeneic stem cell transplantation: incidence in matched-related and matched-unrelated transplant settings.

BACKGROUND: Bacterial, viral, and fungal pathogens frequently cause severe, life-threatening infections in immunocompromised patients after allogeneic hematopoietic stem cell transplantation (SCT). OBJECTIVE: To compare the frequency of infections in patients with matched-related (Group A) or with human leukocyte antigen (HLA)-matched-unrelated donors (Group B). PATIENTS AND METHODS: Patients treated at our transplantation unit between April 2004 and April 2005 were enrolled into this analysis. Documentation comprised demographic data, conditioning treatment, stem cell source, clinical course, as well as microbiological and clinical data and mortality. RESULTS: We analyzed 59 patients, 22 in Group A and 37 in Group B. Both groups were well balanced regarding demographic data. Diagnoses were acute myeloid leukemia (30 of 59 patients, 50.8%), multiple myeloma (15.2%), acute lymphoblastic leukemia (11.9%), and chronic myeloid leukemia (10.2%). Patients in Group A developed infections in 95.5% of the cases compared with 97.3% in patients in Group B. Most frequently detected pathogens were Staphylococcus species, human herpesvirus-6, and Epstein-Barr virus. Three proven fungal infections were detected in Group A compared with 9 proven fungal infections in Group B. Lung infiltrations were observed in equivalent incidence in both groups. Two years after transplantation, 55.9% of patients were alive (Group A: 68.2%; Group B: 48.6%, not significant). CONCLUSION: Allogeneic SCT from HLA-matched-unrelated donors does not have a higher infection risk than patients transplanted from matched-related donors.

Polony analysis of gene expression in ES cells and blastocysts.

Expression profiling of stem cells is challenging due to their small numbers and heterogeneity. The PCR colony (polony) approach has theoretical advantages as an assay for stem cells but has not been applied to small numbers of cells. An assay has been developed that is sensitive enough to detect mRNAs from small numbers of ES cells and from fractions of a single mouse blastocyst. Genes assayed include Oct3, Rex1, Nanog, Cdx2 and GLUT-1. The assay is highly sensitive so that multiple mRNAs from a single blastocyst were easily detected in the same assay. In its present version, the assay is an attractive alternative to conventional RT-PCR for profiling small populations of stem cells. The assay is also amenable to improvements that will increase its sensitivity and ability to analyze many cDNAs simultaneously.

[Fever of unknown origin in malignancies]. / Fieber unklarer Genese bei malignen Erkrankungen.

Fever is a common symptom in patients with malignancies. On the one hand it may be an (initial) symptom of cancer, on the other hand it may occur as a side effect of chemotherapy. Often a precise cause of fever can not be established and in these cases febrile temperatures >38.3 degrees C without proof of infection or relapse/progress of tumor is defined as fever of unknown origin. Especially hematologic neoplasias are accompanied by fever. Here, neoplastic fever must be distinguished from fever following immunosuppressive chemotherapy. In the latter severe infections due to neutropenia induced by cytoreductive chemotherapy is often identified as the cause of fever. These patients display a high morbidity and mortality, especially if an empiric anti-infectious treatment is not administered in time. A meticulous diagnostic work-up is therefore necessary, and until proven otherwise, an infectious cause must be considered and empiric antibiotic treatment initiated.

Safety and efficacy of a new extensively hydrolyzed formula for infants with cow's milk protein allergy.

Cow's milk protein allergy (CMPA) is best treated by complete elimination of cow's milk from the diet. For infants with CMPA who cannot be breast-fed, formulas based on extensively hydrolyzed proteins or on amino acids are the preferred substitutes for cow's milk-based formulas. In this study, we compared the tolerance and growth of infants with CMPA who were fed a new extensively hydrolyzed formula containing lactose (eHF) with those who were fed an amino acid formula (AAF). This was a prospective, multi-center, randomized, reference-controlled study. Seventy-seven infants <12 months old with suspected CMPA were enrolled. In 66 of these, CMPA was confirmed by oral challenge in a double-blind, placebo-controlled food challenge (DBPCFC) or by a medical history of severe allergic reaction to cow's milk and a positive skin prick test. These infants were then tested for their reaction to eHF and AAF in a DBPCFC. All infants tolerated both formulas and were randomized to receive either eHF (n = 34) or AAF (n = 32) for 180 days. Growth (weight, length, and head circumference) and tolerance [skin, gastro-intestinal, and respiratory tract symptoms of allergy] were evaluated after 30, 60, 90, and 180 days. There were no significant differences between the two groups in any of the growth measurements. Length and head circumference were similar to Euro-growth standards, but weight was slightly lower. Gastro-intestinal and respiratory tract symptoms of allergy were also similar in the two groups. However, whereas SCORAD scores for atopic dermatitis remained constant throughout the study in infants-fed eHF, there was a slight decrease in those fed AAF. Infants-fed eHF had significantly fewer incidents of vomiting than infants-fed AAF and a significantly higher frequency of soft stools. The new eHF is safe and well tolerated in infants diagnosed with CMPA.

[Low-dose CT-guided transthoracic lung biopsy for evaluation of non-infectious chronic interstitial lung disease in children]. / Die Niedrigdosis-CT navigierte transthorakale Lungenbiopsie zur Evaluation chronisch-interstitieller, nicht-infektiöser Lungenerkrankungen bei Kindern.

BACKGROUND: Children with interstitial pneumonitis (IP) of unknown origin often have to undergo open lung biopsy to establish a final diagnosis. Open lung biopsy is an invasive procedure with major potential complications. In the meantime, CT-guided transthoracic lung biopsy (TLB) has become a common diagnostic procedure in adults. OBJECTIVE: The aim of this study was to retrospectively evaluate the efficacy and radiation exposure of low-dose CT-guided TLB in children with non-infectious IP of unknown origin. METHODS: Twelve children (7-males, age range: 7 months-15 years) with non-infectious IP of unknown origin and inconclusive clinical tests underwent CT-guided TLB with a 20-gauge biopsy instrument. A low-dose protocol with acquisition of single slices was used on a 16-row CT scanner: 80 kVp, 20 mAs, slice thickness 10 mm. Biopsy specimens were processed by standard histopathological and immunohistochemical techniques and effective doses were individually calculated. RESULTS: All biopsies were performed without major complications. Two children (17 %) developed a small pneumothorax/pulmonary haemorrhage that resolved spontaneously. A final diagnosis could be established in 9/12 patients (75 %) by CT-guided TLB. In 2 patients (17 %) the results of TLB were inconclusive; however, the clinical suspicion could be disproved. Open lung biopsy was performed in 1 patient (8 %), which demonstrated idiopathic pulmonary fibrosis. On average, the effective dose of CT-guided TLB was 0.78 mSv (0.4 - 1.1 mSv). CONCLUSION: Low-dose CT-guided TLB can be a helpful method for investigating children with non-infectious IP of unknown origin thus making open lung biopsy unnecessary. Application of a low-dose protocol leads to a significant reduction of radiation exposure in CT-guided TLB.

Pulmonary sarcoidosis in a 14-year-old boy diagnosed by low-dose CT-guided transthoracic lung biopsy.

Pulmonary sarcoidosis is a rare disease in the pediatric age group, characterized by the presence of epitheloid-cell granulomas. In stage 3 sarcoidosis, pulmonary infiltrates without hilar lymphadenopathy occur. Definitive diagnosis requires a histopathological specimen, which might be difficult to obtain by transbronchial biopsy. Multidetector computed tomography (MDCT)-guided transthoracic lung biopsy (TLB) is a well-established procedure in adults, but has only rarely been applied in children.A 14-year-old boy was admitted to hospital for evaluation of a chronic systemic disease with severe pulmonary manifestation. All investigations, including bronchosopy and bronchoalveolar lavage with microbiological and virological testing, had been negative. MDCT-guided TLB was performed on a 16-section scanner with a low-dose protocol (single slices, 120 kV, 20 mAs), using a 16-gauge biopsy device. The total effective dose was 0.4 mSv for the biopsy procedure. Histopathological examination revealed multiple epitheloid-cell granulomas with giant cells in the absence of microbiological or virological abnormalities. A diagnosis of stage 3 pulmonary sarcoidosis was made and systemic anti-inflammatory therapy was administered, which led to complete remission within weeks. MDCT-guided TLB can be a valuable instrument in assessing pulmonary manifestations of pediatric sarcoidosis, enabling precise histopathological diagnosis and adequate therapy. The use of low-dose protocols can substantially reduce radiation exposure without relevant loss of image information. MDCT-guided lung biopsy should be considered prior to open-lung surgery in selected patients with unclear pulmonary disease.

Carcinoembryonic antigen and humoral antibody response in patients with thyroid carcinoma.

Carcinoembryonic antigen and antibodies to thyroglobulin and to a microsomal fraction of thyroid were measured. Persons examined were normal volunteers, patients with thyroid cancer, and patients with a history of childhood irradiation to the thymus and/or tonsil who were otherwise normal. Elevated antigen and antibodies were most frequently found in the cancer thyroid group. Thyroid cancer patients with no previous history of childhood irradiation were more frequently positive for antigen and antibodies than all other categories studied. Thyroid cancer patients with a previous history of childhood irradiation showed normal frequencies of antigen and antibodies. The results suggest that the antigenic expression and host response to the tumor in patients with thyroid cancer depend on its pathogenesis. Mention is made of similar findings in animal model systems.

Sequential therapy combining clofarabine and T-cell-replete HLA-haploidentical haematopoietic SCT is feasible and shows efficacy in the treatment of refractory or relapsed aggressive lymphoma.

Prognosis is poor for patients with biologically aggressive Non-Hodgkin lymphoma (NHL), refractory to chemotherapy or relapsed after autologous transplantation, especially when no disease control before allogeneic transplantation is achieved. In 16 patients (median age 53, median prior regimes 5) with relapsed or refractory non-remission NHL, we analysed retrospectively the efficacy of a sequential therapy comprising clofarabine re-induction followed by a reduced-intensity conditioning with fludarabine, CY and melphalan, and T-cell-replete HLA-haploidentical transplantation. High-dose CY was utilized post-transplantation. All patients engrafted. Early response (day +30) was achieved in 94%. Treatment-related grade III-IV toxicity occurred in 56%, most commonly transient elevation of transaminases (36%), while there was a low incidence of infections (19% CMV reactivation, 19% invasive fungal infection) and GVHD (GVHD: acute III-IV: 6%; mild chronic: 25%). One-year non-relapse mortality was 19%. After a median follow-up of 21 months, estimated 1- and 2-year PFS was 56 and 50%, respectively, with 11 patients (69%) still alive after 2 years. In summary, sequential therapy is feasible and effective and provides an acceptable toxicity profile in high-risk non-remission NHL. Presumably, cytotoxic reinduction with clofarabine provides enough remission time for the graft-versus lymphoma effect of HLA-haploidentical transplantation to kick in, even in lymphomas that are otherwise chemo-refractory.

Zinc status and vitamin A transport in cystic fibrosis.

Zinc status and the retinol transport system were examined in 18 retinol supplemented cystic fibrosis (CF) patients and 40 age-matched controls. Plasma vitamin A was significantly lower in the CF group as compared to the controls and correlated positively with plasma retinol-binding protein (RBP) in both the CF and control groups. Plasma zinc of the CF group was not significantly lower than controls whereas hair zinc was. Plasma zinc was positively correlated with plasma RBP, vitamin A, and albumin in the CF group but not in the controls. Plasma concentrations of vitamin A, RBP, albumin, and zinc decreased with age in the CF group but not in the controls. The data support previous suggestions that low plasma vitamin A levels in CF are due to defects in the retinol transport system. The zinc status of the CF groups as a whole was judged to be low-normal however a subgroup of CF patients were in the marginal to deficient category. This subgroup also had lower levels of plasma vitamin A and RBP. The data suggest that zinc may be a contributing factor in the low plasma vitamin A/RBP levels of CF patients with marginal or deficient zinc status.

Some biochemical indices of nutrition in treated cystic fibrosis patients.

Postprandial levels of copper, ceruloplasmin, iron, total iron binding capacity, cholesterol, vitamin A, carotene, folic acid, vitamin C, albumin, and total globulins in plasma, of 25-OH-vitamin D in serum, and of glutathione reductase activity, an index of riboflavin status, in erythrocytes were determined in a group of 18 juvenile cystic fibrosis patients receiving specialized outpatient care with attention to diet, vitamin supplementation, and pancreatic enzyme replacement. Bone mineralization was assessed by radiographic and photon beam technique. In the plasma of cystic fibrosis patients, levels were elevated for copper, ceruloplasmin, total globins, and total proteins and were depressed for iron, vitamin D, vitamin A, carotene, and albumin. Cortical thickness was diminished in the patients, but bone density was not. For patients with cystic fibrosis, a relation was established between forced vital capacity and certain biochemical indices in plasma. As forced vital capacity decreased, plasma levels increased for copper, total globulins and total proteins and decreased for albumin.

Detection of activated lymphocyte subsets by fluorescence and MTT staining.

A double staining technique for simultaneously determinating cell surface phenotype and the degree of cell activation is described. As an activation marker, the tetrazolium dye MTT has been used. Cells were incubated for 30 min with MTT. Activated cells yielded a granular staining pattern. Upon termination of the reaction with sodium azide, a double-step immunofluorescence staining procedure using monoclonal antibodies specific for cell surface antigens was performed. The percentage of cells simultaneously displaying MTT formation and fluorescence was microscopically evaluated. Our results demonstrate that MTT staining is expressed concomitantly with the IL-2 receptor and the transferrin receptor. This method permits a simple characterization of activated T cell subsets and can be used clinically to analyse the T cell functions of patients being treated with immunosuppressive agents and patients with acquired immune deficiency syndrome.

Detection of intracellular cytokines by flow cytometry.

During the last years it has become increasingly clear that production of most cytokines is not confined to one cell type. Thus, a method to detect cytokines at the single cell level would be a helpful tool to study the contribution of different cells to cytokine production in heterogeneous cell populations. Recently, Sander et al. (1991) demonstrated that it is possible to detect intracellular cytokines by fixation with paraformaldehyde, permeabilization with saponin and subsequent indirect immunofluorescent staining using fluorescence microscopy. Here, we describe a modified method to increase the specific intracellular staining which enables us to detect IFN-gamma, IL-2 and IL-4 producing cells by single laser flow cytometry. The carboxylic ionophore monensin was used to interrupt intracellular transport processes leading to an accumulation of the cytokine in the Golgi complex. This resulting increase of the signal/noise ratio permitted us to detect weakly fluorescent cells such as IL-4 producing cells. While IL-4 was detected in approximately 1-3% of peripheral mononuclear cells from healthy donors, up to 30% of the cells produced IFN-gamma and nearly 50% IL-2 after phorbol ester and ionomycin stimulation. Microscopic and flow cytometric analysis showed a highly significant correlation. Using three-color flow cytometry it was possible to measure intracellular cytokines and cell surface markers simultaneously. Subpopulations of human T cells (e.g., CD4+ CD45R0-) producing a restricted cytokine pattern could be identified by cell surface staining and were characterized by their cytokine production. Consequently, there was no further need for cell sorting to determine cytokine producing subsets in heterogeneous cell populations. We have tested human T cell clones for intracellular cytokine production and found a high concordance to ELISA analysis of the supernatants. We conclude that detection of intracellular cytokines by flow cytometry is a rapid, easy and semiquantitative assay which may be used to study individual cells in heterogeneous populations as well as to screen homogeneous cells for their cytokine pattern. This method is particularly relevant in view of the accumulating evidence of the functional role that subsets of (T) cells may play in various diseases depending on the pattern of cytokines they produce.

A flow cytometric method for the detection of intracellular basic proteins in unseparated peripheral blood and bone marrow eosinophils.

Eosinophils and their basic proteins play a major role in allergic disease and methods are required to monitor their expression in clinical situations. In this article we describe a flow cytometric method for the detection of intracellular eosinophil cationic protein (ECP) and eosinophil peroxidase (EPO) in unseparated clinical samples. After fixation with parabenzoquinone and permeabilization with n-octyl-beta-D-glucopyranoside, the detection of intracellularly stored proteins was achieved using of monoclonal antibodies against ECP (EG1, EG2) and EPO in combination with an FITC-labeled second step antibody. Confocal microscopy was used to demonstrate the intracellular origin of the fluorescent signal. Fixation with parabenzoquinone was superior to a previously described protocol using paraformaldehyde, since it reduces non-specific binding of FITC to the basic proteins in eosinophils. Fixation and permeabilization do not alter the light scatter characteristics of eosinophils in contrast to other leukocytes and thus permit gating on eosinophils without prior purification. Furthermore, the procedure does not alter the detection of cell surface antigens on eosinophils and simultaneous measurements of surface antigens and intracellular proteins is possible. We have used different clinical samples (peripheral blood, bone marrow cells) to demonstrate differences in the expression of ECP and EPO. We conclude that the detection of intracellular eosinophil proteins by flow cytometry is a rapid, easy and semiquantitative procedure which may be used to study their expression in diseases where eosinophils are involved.

Induction of specific tolerance to ingested soluble protein in neonatal rabbits.

The immune response of adult rabbits to low concentrations of BSA in their drinking water has been a useful model to study systemic immunity initiated in gut-associated lymphoid tissue. In the present study, this model was applied to neonatal rabbits. 21 New Zealand white neonatal rabbits were fed a cow-milk formula containing 0.17% BSA from the 5th to the 32nd day of life. At this time, anti-BSA was detected in only 5 animals. A subsequent intravenous injection of 50 mg BSA demonstrated a weak anti-BSA response in 6 and complete tolerance in 15 animals. Specificity of this tolerance was demonstrated by a vigorous response to 100 mg HSA, given at 60 days of age, in all of 9 animals tested. At 8 months of age, 2 of 3 animals still failed to respond to intravenous BSA, one rabbit had a low primary-type response. Determination of absorbed antigenic BSA on day 32 showed a mean of 1.09 +/- 0.47 (S.E.) microgram BSA per ml of serum, i.e. a considerably higher concentration than seen in adult animals fed similar antigen concentrations. These observations suggest that orally induced tolerance in neonatal rabbits may be due to an effect on systemic lymphoid tissue following increased antigen absorption rather than a direct antigen effect on gut-associated lymphoid tissue.