Quasi-periodic X-ray eruptions years after a nearby tidal disruption event.

Quasi-periodic eruptions (QPEs) are luminous bursts of soft X-rays from the nuclei of galaxies, repeating on timescales of hours to weeks1-5. The mechanism behind these rare systems is uncertain, but most theories involve accretion disks around supermassive black holes (SMBHs) undergoing instabilities6-8 or interacting with a stellar object in a close orbit9-11. It has been suggested that this disk could be created when the SMBH disrupts a passing star8,11, implying that many QPEs should be preceded by observable tidal disruption events (TDEs). Two known QPE sources show long-term decays in quiescent luminosity consistent with TDEs4,12 and two observed TDEs have exhibited X-ray flares consistent with individual eruptions13,14. TDEs and QPEs also occur preferentially in similar galaxies15. However, no confirmed repeating QPEs have been associated with a spectroscopically confirmed TDE or an optical TDE observed at peak brightness. Here we report the detection of nine X-ray QPEs with a mean recurrence time of approximately 48 h from AT2019qiz, a nearby and extensively studied optically selected TDE16. We detect and model the X-ray, ultraviolet (UV) and optical emission from the accretion disk and show that an orbiting body colliding with this disk provides a plausible explanation for the QPEs.

In end stage osteoarthritis, cartilage tissue pentosidine levels are inversely related to parameters of cartilage damage.

OBJECTIVES: Age is the most prominent predisposition for development of osteoarthritis (OA). Age-related changes of articular cartilage are likely to play a role. Advanced glycation endproducts (AGEs) accumulate in cartilage matrix with increasing age and adversely affect the biomechanical properties of the cartilage matrix and influence chondrocyte activity. In clinical studies AGEing of cartilage and its relation to actual cartilage damage can only be measured by surrogate markers (e.g., serum, skin or urine AGE levels and imaging or biochemical markers of cartilage damage). In this study actual cartilage AGE levels were directly related to actual cartilage damage by use of cartilage obtained at joint replacement surgery. METHODS: Cartilage and urine samples were obtained from 69 patients undergoing total knee replacement. Samples were analyzed for pentosidine as marker of AGE. Cartilage damage was evaluated macroscopically, histologically, and biochemically. RESULTS: Cartilage and urine pentosidine both increased with increasing age. The higher the macroscopic, histological, and biochemical cartilage damage the lower the cartilage pentosidine levels were. In multiple regression analysis age is not found to be a confounder. CONCLUSION: There is an inverse relation between cartilage AGEs and actual cartilage damage in end-stage OA. This is likely due to ongoing (ineffective) increased turnover of cartilage matrix proteins even in end stage disease.

Serum adipokines in osteoarthritis; comparison with controls and relationship with local parameters of synovial inflammation and cartilage damage.

OBJECTIVE: Adipose tissue is an endocrine tissue releasing adipokines suggested to be involved in the pathogenesis of osteoarthritis (OA). Nevertheless, their relative contribution and exact mechanisms are still ambiguous. The aim of this study is to compare serum adipokine levels between end-stage knee OA patients and controls and to relate these serum levels to local parameters of cartilage damage and synovial inflammation. METHODS: Serum was collected from 172 severe knee OA patients, shortly before total knee replacement (TKR) surgery and from 132 controls without radiographic knee OA [Kellgren & Lawrence (K&L) = 0]. Serum adiponectin, leptin, and resistin levels were measured by enzyme-linked immunosorbent assay (ELISA). Cartilage and synovial tissue were collected at TKR surgery and assessed for cartilage degeneration and synovial inflammation by histochemistry and biochemical analyses. RESULTS: The adipokine levels were all distinctly higher in OA patients as compared to controls. Especially adiponectin and leptin were associated with female gender (stand beta = 0.239 and 0.467, respectively, P < 0.001) and body mass index (BMI) (stand beta = -0.189 and 0.396, respectively, P < 0.001). No associations between serum levels of adipokines and cartilage damage (histochemistry, proteoglycan content) were found whereas weak but positive associations with synovial inflammation were found [adiponectin and interleukin-1ß (IL-1ß), stand beta = 0.172, P = 0.02; resistin and histology, stand beta = 0.183, P = 0.034, adjusted for demographics]. CONCLUSION: This study suggests an important involvement of adipokines in OA patients considering their high serum levels compared to controls. Associations of systemic adipokines with local synovial tissue inflammation were found, although not represented by similar relations with cartilage damage, suggesting that adipokines are of relevance in the inflammatory component of OA.

Stromal interaction essential for vascular endothelial growth factor A-induced tumour growth via transforming growth factor-ß signalling.

BACKGROUND: High vascular endothelial growth factor (VEGFA) levels at the time of diagnosis confer a worse prognosis to multiple malignancies. Our aim was to investigate the role of VEGFA in promoting tumour growth through interaction with its environment. METHODS: HL-60 cells were transduced with VEGFA165 or control vector using retroviral constructs. Control cells (n=7) or VEGFA165 cells (n=7) were subcutaneously injected into NOD/SCID mice. Immunohistochemistry of markers for angiogenesis (CD31) and cell proliferation (Ki67) and gene expression profiling of tumours were performed. Paracrine effects were investigated by mouse-specific cytokine arrays. RESULTS: In vivo we observed a twofold increase in tumour weight when VEGFA165 was overexpressed (P=0.001), combined with increased angiogenesis (P=0.002) and enhanced tumour cell proliferation (P=0.001). Gene expression profiling revealed human genes involved in TGF-ß signalling differentially expressed between both tumour groups, that is, TGFBR2 and SMAD5 were lower expressed whereas the inhibitory SMAD7 was higher expressed with VEGFA165. An increased expression of mouse-derived cytokines IFNG and interleukin 7 was found in VEGFA165 tumours, both described to induce SMAD7 expression. CONCLUSION: These results suggest a role for VEGFA-driven tumour growth by TGF-ß signalling inhibition via paracrine mechanisms in vivo, and underscore the importance of stromal interaction in the VEGFA-induced phenotype.

Istaroxime treatment ameliorates calcium dysregulation in a zebrafish model of phospholamban R14del cardiomyopathy.

The heterozygous Phospholamban p.Arg14del mutation is found in patients with dilated or arrhythmogenic cardiomyopathy. This mutation triggers cardiac contractile dysfunction and arrhythmogenesis by affecting intracellular Ca2+ dynamics. Little is known about the physiological processes preceding induced cardiomyopathy, which is characterized by sub-epicardial accumulation of fibrofatty tissue, and a specific drug treatment is currently lacking. Here, we address these issues using a knock-in Phospholamban p.Arg14del zebrafish model. Hearts from adult zebrafish with this mutation display age-related remodeling with sub-epicardial inflammation and fibrosis. Echocardiography reveals contractile variations before overt structural changes occur, which correlates at the cellular level with action potential duration alternans. These functional alterations are preceded by diminished Ca2+ transient amplitudes in embryonic hearts as well as an increase in diastolic Ca2+ level, slower Ca2+ transient decay and longer Ca2+ transients in cells of adult hearts. We find that istaroxime treatment ameliorates the in vivo Ca2+ dysregulation, rescues the cellular action potential duration alternans, while it improves cardiac relaxation. Thus, we present insight into the pathophysiology of Phospholamban p.Arg14del cardiomyopathy.

Mycobacterium bovis BCG-itis and cervical lymphadenitis due to Salmonella enteritidis in a patient with complete interleukin-12/-23 receptor beta1 deficiency.

Mendelian susceptibility to mycobacterial disease (MSMD) is a rare disorder with predisposition to severe, sometimes lethal, disease caused by otherwise poorly virulent, non-tuberculous environmental mycobacteria and poorly virulent salmonellae. In patients with MSMD, mutations have been identified in five genes that encode for the proteins IL-12/IL-23p40, IL-12/ IL-23Rbeta1, IFN-R1, IFN-gammaR2 and STAT1. These proteins play important roles in the type-1 cytokine pathway, which is crucial for human host defence against intracellular pathogens such as mycobacteria and salmonellae. We report a girl with mild Mycobacterium bovis Bacille Calmette-Guérin (BCG) disease and Salmonella enteritidis cervical lymphadenitis. Despite treatment, she has remained a fecal carrier of S. enteritidis for the past 14 years. She was found to have complete IL-12/IL-23Rbeta1 deficiency. A homozygous r.518G>C IL12RB1 mutation was identified, leading to a non-functional R173P substitution in the IL-12/IL-23Rbeta1 protein. This mutation abrogated IL-12/IL-23Rbeta1 cell-surface expression and resulted in complete lack of T cell responsiveness to both IL-12 and IL-23.

Pelvic organ prolapse and overactive bladder.

AIMS: In this review we try to shed light on the following questions: *How frequently are symptoms of overactive bladder (OAB) and is detrusor overactivity (DO) present in patients with pelvic organ prolapse (POP) and is there a difference from women without POP? *Does the presence of OAB symptoms depend on the prolapsed compartment and/or stage of the prolapse? *What is the possible pathophysiology of OAB in POP? *Do OAB symptoms and DO change after conservative or surgical treatment of POP? METHODS: We searched on Medline and Embase for relevant studies. We only included studies in which actual data about OAB symptoms were available. All data for prolapse surgery were without the results of concomitant stress urinary incontinence (SUI) surgery. RESULTS: Community- and hospital-based studies showed that the prevalence of OAB symptoms was greater in patients with POP than without POP. No evidence was found for a relationship between the compartment or stage of the prolapse and the presence of OAB symptoms. All treatments for POP (surgery, pessaries) resulted in an improvement in OAB symptoms. It is unclear what predicts whether OAB symptoms disappear or not. When there is concomitant DO and POP, following POP surgery DO disappear in a proportion of the patients. Bladder outlet obstruction is likely to be the most important mechanism by which POP induces OAB symptoms and DO signs. However, several other mechanisms might also play a role. CONCLUSIONS: There are strong indications that there is a causal relationship between OAB and POP.

Mechanical analysis of the preferred strategy selection in human stumble recovery.

We use simple walking models, based on mechanical principles, to study the preferred strategy selection in human stumble recovery. Humans typically apply an elevating strategy in response to a stumble in early swing and midswing, for which the perturbed step is lengthened in a continuation of the original step. A lowering strategy is executed for stumbles occurring at midswing or late swing, for which the perturbed swing foot is immediately placed on the ground and the recovery is executed in the subsequent step. There is no clear understanding of why either strategy is preferred over the other. We hypothesize that the human strategy preference is the result of an attempt to minimize the cost of successful recovery. We evaluate five hypothesized measures for recovery cost, focusing on the energetic cost of active recovery limb placement. We determine all hypothesized cost measures as a function of the chosen recovery strategy and the timing of the stumble during gait. Minimization of the cost measures based on the required torque, impulse, power and torque/time results in a humanlike strategy preference. The cost measure based on swing work does not predict a favorable strategy as a function of the gait phase.

The chondroprotective effect of selective COX-2 inhibition in osteoarthritis: ex vivo evaluation of human cartilage tissue after in vivo treatment.

OBJECTIVE: Recent in vitro studies showed that celecoxib, a selective cyclooxygenase (COX)-2 inhibitor, protects human osteoarthritic cartilage tissue from degeneration. The objective was to substantiate these beneficial effects in an in vivo (clinical) study with celecoxib treatment of patients with severe knee osteoarthritis (OA) and subsequent evaluation of cartilage tissue ex vivo. METHODS: Patients with knee OA were treated 4 weeks prior to total knee replacement surgery with either celecoxib 200mg b.d., indomethacin 50mg b.d., or received no treatment. During surgery cartilage and synovium were collected and analyzed in detail ex vivo. RESULTS: When compared to non-treated patients, patients treated with celecoxib showed significant beneficial effects on proteoglycan synthesis, -release, and -content, confirming the in vitro data. In the indomethacin group, no significant differences were found compared to the control group. On the contrary, a tendency towards a lower content and lower synthesis rate was found. In the treated groups prostaglandin-E(2) levels were lower than in the control group, indicating COX-2 inhibition. Ex vivo release of interleukin-1 beta (IL-1 beta) and tumour necrosis factor-alpha by synovial tissue was decreased by treatment with celecoxib, whereas in the indomethacin group only IL-1 beta release was decreased. CONCLUSION: Using this novel approach we were able to demonstrate an in vivo generated chondrobeneficial effect of celecoxib in patients with end stage knee OA.

[Male urinary incontinence]. / Incontinentie bij de man.

*Urinary incontinence in males is gaining increasingly more attention. *Male urinary incontinence can be classified as storage incontinence due to overactive bladder syndrome or stress incontinence due to urethral sphincter dysfunction. *Most patients benefit from the currently available treatment options for overactive bladder, which include physiotherapy, medication, botulinum A toxin injections and neuromodulation techniques. *The number of radical prostatectomies performed for prostate cancer is increasing; this intervention can lead to stress incontinence due to sphincter weakness. *Various treatment options are available for stress incontinence due to sphincter weakness. *In addition to physiotherapy, treatment options also include the artificial urinary sphincter, which has been available for decades. *New treatments include para-urethral balloons and male slings. The value of these approaches must be proven in the coming years.

Adrenergic regulation of conduction velocity in cultures of immature cardiomyocytes.

During cardiac maturation, increased exposure of the heart to circulating catecholamines correlates with increased conduction velocity and growth of the heart. We used an in vitro approach to study the underlying mechanisms of adrenergic stimulation induced changes in conduction velocity. By combining functional measurements and molecular techniques, we were able to demonstrate that the increased conduction velocity after beta-adrenergic stimulation is probably not caused by changes in intercellular coupling. Instead, RT-PCR experiments and action potential measurements have shown an increased excitability that may well explain the observed increase in conduction velocity. Apart from being relevant to cardiac maturation, our findings are relevant in the context of stem cells and cardiac repair. Preconditioning of stem cell derived cardiomyocytes may help to enhance electrical maturation of de novo generated cardiomyocytes and consequently reduce their proarrhythmogenic potential. (Neth Heart J 2008;16:106-9.).

Plasma granulysin levels and cellular interferon-gamma production correlate with curative host responses in tuberculosis, while plasma interferon-gamma levels correlate with tuberculosis disease activity in adults.

Granulysin is a recently identified cytolytic protein which is expressed by human cytotoxic T-lymphocytes and natural killer (NK)-cells, and has broad antimicrobial and tumoricidal activity. Circulating granulysin levels are associated with T- and NK-cell activity, and may thus reflect protection-associated cellular immune responses. In a case-control study in Indonesia, a highly tuberculosis (TB)-endemic country, we therefore determined plasma granulysin levels in adults with active pulmonary TB before, during, and after TB treatment, both in mild/moderate-TB and advanced-TB patients, and compared these to healthy neighbourhood controls. Adults with active pulmonary TB had significantly lower plasma granulysin levels compared to controls. After 2 months of anti-TB therapy, levels in TB patients had significantly increased, reaching values similar to those in controls. Plasma granulysin levels further increased after completion of TB therapy, being significantly higher than those in controls. Plasma granulysin levels correlated inversely with TB disease activity but not with TB disease severity. In contrast, plasma interferon-gamma (IFN-gamma) levels were significantly higher in active TB cases than in controls, normalised during treatment and correlated with both TB disease activity and TB disease severity. At the cellular level, granulysin and IFN-gamma expression both correlated inversely with disease activity. Interestingly, granulysin was predominantly expressed by IFN-gamma negative T-cells, suggesting that the cellular sources of IFN-gamma and granulysin in TB are partly non-overlapping. The observation that plasma granulysin levels and cellular IFN-gamma production correlate with curative host responses in pulmonary tuberculosis points to a potentially important role of granulysin, next to IFN-gamma, in host defence against M. tuberculosis.

A 2015 focus on preventing drug-induced arrhythmias.

Drug-induced Torsade de Pointes arrhythmia is a life-threatening adverse effect feared by pharmaceutical companies. For the last decade, the cardiac safety guidelines have imposed human ether-a-go-go-related gene channel blockade and prolongation of QT interval as surrogates for proarrhythmic risk propensity of a new chemical entity. Suffering from a lack of specificity, this assessment strategy led to a great amount of false positive outcomes. Therefore, this review will discuss new pharmaceutical strategies: the cardiac safety proposal that recently emerged, the Comprehensive in vitro Proarrhythmia Assay, combining in vitro assays that integrate effects on main cardiac ion channels, with computational models of human ventricular action potential as well as assays using human stem cell-derived cardiomyocytes for an improved prediction of drug's proarrhythmic liability, alternative pharmacological perspectives as well as the current treatment of drug-induced long QT syndrome.

Quantifying Beta-Galactosylceramide Kinetics in Cerebrospinal Fluid of Healthy Subjects Using Deuterium Labeling.

Therapeutics promoting myelin synthesis may enhance recovery in demyelinating diseases, such as multiple sclerosis. However, no suitable method exists to quantify myelination. The turnover of galactosylceramide (myelin component) is indicative of myelination in mice, but its turnover has not been determined in humans. Here, six healthy subjects consumed 120 mL 70% D2 O daily for 70 days to label galactosylceramide. We then used mass spectrometry and compartmental modeling to quantify the turnover rate of galactosylceramide in cerebrospinal fluid. Maximum deuterium enrichment of body water ranged from 1.5-3.9%, whereas that of galactosylceramide was much lower: 0.05-0.14%. This suggests a slow turnover rate, which was confirmed by the model-estimated galactosylceramide turnover rate of 0.00168 day-1 , which corresponds to a half-life of 413 days. Additional studies in patients with multiple sclerosis are needed to investigate whether galactosylceramide turnover could be used as an outcome measure in clinical trials with remyelination therapies.

Human deficiencies in type 1 cytokine receptors reveal the essential role of type 1 cytokines in immunity to intracellular bacteria.

Studies on patients with idiopathic, severe infections due to poorly pathogenic mycobacteria and Salmonella have revealed that many of these patients are unable to produce or respond to interferon-gamma (IFN-gamma). This inability results from causative, deleterious genetic mutations in either one of four different genes in the type 1 cytokine cascade, encoding interleukin-12Rbeta1 (IL-12Rbeta1), IL-12p40, IFN-gammaR1 or IFN-gammaR2. The immunological phenotypes resulting from the seven groups of complete or partial deficiencies in type 1 cytokine (receptor) genes that have been distinguished thus far will be summarized and discussed, and placed in a broader context in relation to disease susceptibility.

The pharmacological profile of Org 6906, a potential non-sedative antidepressant that combines monoamine uptake inhibition with alpha 2-adrenolytic activity.

(dl)-(5 alpha,8 alpha,9 alpha)-5,8,9,10-Tetrahydro-5,9- methanobenzocycloocten-8-amine hydrochloride (Org 6906) is a potential new antidepressant agent, with a neurochemical profile quite different from that of the classical tricyclic antidepressant drugs. The compound was found active in behavioural tests which are considered to be predictive for antidepressant activity, such as the muricidal test in the rat and the acquired immobility model. Neurochemical studies showed that Org 6906 was an inhibitor of the reuptake of monoamines both in vitro and ex-vivo without having appreciable anticholinergic, antihistaminergic or alpha 1-adrenolytic activity. The facilitatory effect on monoaminergic neurotransmission was confirmed by the reversal of hypothermia induced by reserpine. The drug Org 6906 appeared to have selective alpha 2-adrenolytic properties. It facilitated potassium-stimulated release of noradrenaline from slices of cortex, displaced [3H]rauwolscine and [3H]dihydroergocryptine from their binding sites but only weakly blocked alpha 1-adrenoceptors. The alpha 2-adrenolytic properties were also apparent in behavioural interaction models. The compound antagonized the sleep-inducing effects of clonidine in chicks and mice and it antagonized the mydriasis induced by clonidine in the rat. Finally, it was shown that the two enantiomers of Org 6906 contributed almost equally to the relevant neurochemical and behavioural properties.

Neurochemical and autonomic pharmacological profiles of the 6-aza-analogue of mianserin, Org 3770 and its enantiomers.

The neurochemical and autonomic pharmacological profile of 1,2,3,4,10, 14b-hexahydro-2-methyl-pyrazino[2,1-a]pyrido[2,3-c]pyrido[2, 3-c] [2] benzazepine [+/-)Org 3770) and the related antidepressant drug, mianserin, have been compared. The uptake of [3H]noradrenaline ([3H]NA) in vitro was weakly affected by (+/-)Org 3770 (pKi = 5.6) in contrast to mianserin (pKi = 7.4). Both (+/-)Org 3770 and mianserin facilitated the release of [3H]NA in slices of cortex. The effects of NA mediated by alpha 2-adrenoceptors on the release of both [3H]NA or [3H]serotonin ([3H]5-HT) were antagonized by (+)Org 3770 with pKi values of 8.4 and 8.1, respectively. However, (-)Org 3770 only antagonized the effect of NA on the release of [3H]5-HT (pA2 = 7.7). The binding of [3H]rauwolscine to alpha 2-adrenoceptors was inhibited by (+/-)Org 3770 and mianserin with identical affinity (pKi = 7.0), whereas the binding of [3H]prazosin to alpha 1-adrenoceptors was less potently affected by (+/-)Org 3770 (pKi = 6.4) than by mianserin (pKi = 7.1). A similar difference was found for alpha 1- and alpha 2-adrenoceptors in vas deferens of the rat. The binding of [3H]mianserin to 5-HT2 receptors was less potently blocked by (+/-)Org 3770 (pKi = 8.1) than by mianserin (pKi = 9.4) while the binding of [3H]mepyramine to histamine-1 receptors was more potently affected by (+/-)Org 3770 (pKi = 9.3) than by mianserin (pKi = 8.75). The binding of [3H]quinuclidinylbenzilate to muscarinic cholinergic receptors was blocked equally by (+/-)Org 3770 (pKi = 6.1) and mianserin (pKi = 6.3). Similar data on tryptamine-D, histamine-1 and muscarinic cholinergic receptors in isolated organs were obtained. A prominent role for the blockade of alpha 2-adrenoceptors in the therapeutic effects of mianserin and (+/-)Org 3770 in depression is suggested, probably excluding a role of inhibition of the uptake of NA.

Adhesive capacity of human long-term bone marrow cultures from normals and patients with acute myeloid leukaemia: the influence of adhesion molecules.

In order to study the adhesive interactions of the human bone marrow microenvironment and acute myeloid leukaemic cells, we investigated the binding capacity of KG-1 cells upon human long-term bone marrow cultures derived from 17 healthy volunteers and 12 patients with acute myeloid leukemia. Adhesion was measured using a 51-chromium labelling assay. Adhesion of KG-1 cells upon 'normal' stromal layers: 33% +/- 4.0, n = 17 (mean +/- SEM) was higher as compared to the binding to 'leukaemic' stromas: 24% +/- 3.7, n = 12 (p < 0.05). Blocking monoclonal antibodies against adhesion molecules reduced the binding of KG-1 cells upon 'normal' stroma, when anti-VLA4 (p < 0.03), anti-Mac1 (p < 0.03) and anti-p150/95 (p < 0.04) were used. Binding of KG-1 cells on 'leukaemic' stromas was partly inhibited by anti-VCAM1 (p < 0.03). Blocking achieved by single or combined antibodies was never complete, suggesting that the adhesion is a multifactorial process, including a variety of adhesion molecules and/or adhesion mechanisms.

VLA molecule expression may be involved in the release of acute myeloid leukaemic cells from the bone marrow.

Acute myeloid leukaemia (AML) cells have a variable capacity to egress from bone marrow into peripheral blood. This may be due to a variable lack of adhesion molecules on leukaemic cells. The expression of VLA1, 3, 4, 5, 6, beta 1-chain, LFA1, beta 2-chain, ICAM1 and NCAM appeared to be higher in bone marrow as compared to peripheral blood leukaemic cells, although this only reached significance for beta 1-chain (p less than 0.01). The number of cases with more than 20% positive cells in bone marrow leukaemic cells was lower in immature FAB-subtypes (M1, M5a) as opposed to more mature subtypes (M2, M3, M4, M5b) for the adhesion molecules tested. This reached significance for VLA5 (p less than 0.05) and beta 1-chain (p less than 0.007), while there was trend for VLA4. It is discussed that VLA4 and 5 may play a role in the release of leukaemic cells from the bone marrow.

B cells specific for bromelain-treated erythrocytes are not derived from adult rat bone marrow.

As part of an evolutionary layered hematopoietic system, the B lymphocyte compartment consists of different lineages of B lymphocytes, which evolve sequentially during ontogeny. In mice, there is ample evidence for the existence of at least two lineages, a layer of B-1 cells (Ly-1 B cells) and the evolutionary more advanced layer consisting of conventional B cells. In a previous study we were unable to detect B-1 cells in the rat as determined by phenotypic markers. Here we studied the possible existence of putative B-1 cells in the rat based on some functional and developmental characteristics as have been described for mouse B-1 cells. We show that B cells secreting antibodies that recognize bromelain-treated mouse red blood cells (BrMRBC) can be identified in rat spleen, whereas these cells (in contrast to DNP-specific B cells) are virtually absent in lethally X-irradiated and bone marrow (BM) reconstituted animals. The number of anti-rMRBC-secreting B cells could not be restored to control levels by reconstitution with fetal liver cells or by cotransfer of 10(7) cells from peritoneal cavity, lymph node or Peyer's patches or up to 2 x 10(8) splenocytes. Although our findings thus suggest that B-1 cells (or B-1 like cells) may be present in rats, formal proof for the existence of such a lineage in rats awaits definition of these cells at the progenitor level.