Evidence that endogenous ecotropic virus is not expressed in AKR thymic lymphoid cells of chimeric hosts.

AKR/J thymocytes derived from fetal liver cells do not produce virus when they differentiate in lethally irradiated B10.K mice, whereas spleen and bone marrow cells are virus producers. In contrast, B10.K thymocytes that differentiate in lethally irradiated AKR mice become virus producers. These results suggest that infection of the thymus in AKR mice is initiated in thymic stromal cells.

Identification of a variant of gross leukemia virus that induces disease in mice inoculated as adults.

Gross murine leukemia virus normally induces leukemia (thymic lymphoma) in mice inoculated as neonates, but not as adults. We have isolated an apparent variant of this virus which induces thymomas when inoculated i.p. into susceptible adult mice. Using H-2 congenic BALB and C57BL mice, susceptibility to virus-induced thymomagenesis was found to be linked to the H-2 complex. In addition, a radioresistant immune mechanism leading to inhibition of tumor growth was observed in mice with a C57BL but not a BALB background.

The genetic basis of susceptibility to leukemia induction in mice by 3-methylcholanthrene applied percutaneously.

Susceptibility to leukemia induction in mice by skin painting with 3-methylcholanthrene (MCA) is strain-specific, occurring only in strains relatively resistant to MCA-induced skin tumors. The Ah locus, which has a dominant allele (Ahb) for inducibility of the aryl hydrocarbon hydroxylase (AHH) enzyme system and a recessive allele (Ahd) for noninducibility, appears to be the major determinant of this trait. MCA-painted mice of strains and crosses carrying the Ahb allele usually show a high incidence of skin tumors (papillomas which may evolve into malignant tumors) and little or no leukemia, whereas in mice homozygous for the Ahd allele the treatment usually induces a high incidence of leukemia and few or no skin tumors. Among mice of a segregating backcross generation including both Ahb/Ahd heterozygotes and Ahd homozygotes, the occurrence of skin tumors was correlated directly with AHH inducibility and inversely with the leukemic response. Mice of Ahb strains with a high level of endogenous murine leukemia (MuLV) expression (C58, PL) show a much weaker skin tumor response than expected but no increase in leukemia incidence, and this observation tends to confirm the previous finding that MuLV infection of mice of low-MuLV strains results in reduced susceptibility to MCA tumorigenesis.

Neonatal exposure to thymotropic gross murine leukemia virus induces virus-specific immunologic nonresponsiveness.

Neonatal exposure to Gross murine leukemia virus results in a profound inhibition of the virus-specific T and B cell responses of adult animals. Animals exposed to virus as neonates exhibit a marked depression in virus-specific T cell function as measured by the virtual absence of in vivo delayed type hypersensitivity responses and in vitro proliferative responses to virally infected stimulator cells. Further, serum obtained from neonatally treated mice failed to either immunoprecipitate viral proteins or neutralize virus in an in vitro plaque assay, suggesting the concurrent induction of a state of B cell hyporesponsiveness. The specificity of this effect at the levels of both T and B cells was demonstrated by the ability of neonatally treated mice to respond normally after adult challenge with either irrelevant reovirus or influenza virus. The replication of Gross virus within both stromal and lymphocytic compartments of the neonatal thymus suggests that thymic education plays a key role in the induction of immunologic nonresponsiveness to viruses.

A role for complement receptor-like molecules in iron acquisition by Candida albicans.

Candida albicans, an opportunistic fungal pathogen of humans, is dependent upon iron for growth. Consequently, human serum inhibits C. albicans growth due to the presence of high affinity iron-binding proteins that sequester serum iron, making it unavailable for use by the organism. We report that in the inhibitory environment of human serum, the growth of C. albicans can be restored by the addition of exogenous hemoglobin or heme, but not by protoporphyrin IX, the heme precursor that does not contain iron. We further report that C. albicans can utilize cell surface proteins that are homologues of the mammalian complement receptors (CR) to rosette complement-coated red blood cells (RBC) and obtain RBC-derived iron for growth. The ability of Candida to acquire RBC-derived iron under these conditions is dependent upon Candida-RBC rosetting mediated by CR-like molecules. Unopsonized RBC do not support Candida growth in serum, and restoration of Candida growth in serum by complement-opsonized RBC is inhibited by monoclonal antibodies to the human CR type 3 (CR3). In addition, activation of the human alternative pathway of complement by Candida leads to "bystander" deposition of C3 fragments on the surface of autologous, unopsonized RBC, generating the ligands necessary for Candida-RBC rosetting. These results suggest that C. albicans has evolved a unique strategy for acquiring iron from the host, which exploits the host complement system, and which may contribute to the pathogenic potential of the organism.

Surface expression of a T cell receptor beta (TCR-beta) chain in the absence of TCR-alpha, -delta, and -gamma proteins.

The antigen receptor expressed by mature T cells has been described as a disulfide-linked alpha/beta or gamma/delta heterodimer noncovalently associated with CD3, a complex of transmembrane proteins that communicates signals from the T cell receptor (TCR) to the cell interior. Studies suggest that all component chains must assemble intracellularly before surface expression can be achieved. We described, however, a CD4+/CD8+ transformed murine thymocyte, KKF, that expresses surface TCR-beta chains in the absence of gamma, delta, and alpha proteins; these beta chains are only weakly associated with CD3-epsilon and CD3-zeta. Furthermore, KKF responds differently to stimulation through TCR-beta and CD3-epsilon, a functional dissociation that has been ascribed to a CD4+/CD8+ subpopulation of normal thymocytes. KKF's unique TCR structure may offer an explanation for the functional anomalies observed.

Monocular spatial distortions induced by marked accommodation.

Contraction of the ciliary muscle during marked accommodation causes the leading edge of the retina to advance as much as 0.5 centimeter. Near the posterior pole of the eye, the upward and downward extensional strains on the retina should be reasonably balanced. In the horizontal meridian an asymmetry is introduced because of the nasal location of the optic nerve head. Observers were asked to bisect the space between two parallel lines while fixating a movable line lying near the midpoint of the two lines. The test was conducted with the target far from and near the subject, in the horizontal and vertical meridians, and was repeated with accommodation paralyzed by a cycloplegic agent. Marked accommodation induced significant spatial distortions in the horizontal meridian. The effect is largely retinal.

Rational design of cytotoxic T-cell inhibitors.

This study describes the use of the CD8/major histocompatibility complex (MHC) class I crystal structure as a template for the de novo design of low-molecular-weight surface mimetics. The analogs were designed from a local surface region on the CD8 alpha-chain directly adjacent to the bound MHC class I, to block the protein associations in the T-cell activation cluster that occur upon stimulation of the cytotoxic T lymphocytes (CTLs). One small conformationally restrained peptide showed dose-dependent inhibition of a primary allogeneic CTL assay while having no effect on the CD4-dependent mixed lymphocyte reaction (MLR). The analog's activity could be modulated through subtle changes in its side chain composition. Administration of the analog prevented CD8-dependent clearance of a murine retrovirus in BALB/c mice. In C57BL/6 mice challenged with the same retrovirus, the analog selectively inhibited the antiviral CTL responses without affecting the ability of the CTLs to generate robust allogeneic responses.

Construction of a DBA/2.Fv-2r congenic strain. Apparent lethality of the homozygous Fv-2r genotype: brief communication.

From the (C57BL/6 X DBA/2)F1 cross, 13 serial backcrosses to the DBA/2 parental mouse strain were bred with selection by progeny testing in each generation for the Fv-2s/Fv-2r heterozygous genotype. Intercrossing heterozygotes of the 13th backcross generation produced no Fv-2r/Fv-2r homozygotes. Homozygosity for the Fv-2r allele thus appeared to be lethal on a DBA/2 background and in the absence of protector gene(s) of the C57BL strain.

The Fv-2r resistance gene in mice: its effect on spleen colony formation by Friend virus-transformed cells.

To determine the mechanism by which the recessive Fv-2r gene confers complete resistance to spleen focus formation and to the induction of early splenomegaly characteristic of the Friend virus (FV) disease syndrome, we compared the parameters of FV infection in susceptible DBA/2 (D2) (Fv-1n, Fv-2s) and partially congenic D2.Fv-2r (Fv-1n, Fv-2r) mice. After infecting these mice with N-tropic FV complex, we followed the replication of spleen focus-forming virus (SFFV) and the generation of SFFV-transformed tumor colony-forming cells (CFC) in their spleens. By both parameters D2.Fv-2r mice were 20- to 100-fold less susceptible than DBA/2 controls, but the inhibition was only partial. Transplantation of washed spleen cells from SFFV-infected DBA/2 mice resulted in equal growth and recovery of tumor CFC from both D2.Fv-2r and Fv-2s mice. However, these tumor cells grew as colonies in Fv-2s mice, whereas they grew diffusely in the spleens of D2.Fv-2r hosts and did not develop into macroscopically or microscopically visible colonies. Thus the completeness of the resistance to spleen focus formation that defines the Fv-2r gene was reflected only in the complete suppression of the colonial growth of tumor cells, whereas the other parameters of infection showed no or only partial inhibition.

Cyclin B1 availability is a rate-limiting component of the radiation-induced G2 delay in HeLa cells.

Irradiation of tumor cells results in a G2 delay, which has been postulated to allow DNA repair and cell survival. The G2 delay after irradiation is marked in HeLa and other cells by delayed expression of cyclin B1. To test whether this depression of cyclin B1 contributes to the G2 delay, we induced cyclin B1 expression in irradiated HeLa cells using a dexamethasone-inducible promoter. Induction of cyclin B1 after radiation abrogated the G2 delay by approximately doubling the rate at which the cells reentered mitosis, whereas dexamethasone itself had no effect. However, overexpression of cyclin B1 did not eliminate the G2 delay in irradiated cells. In unirradiated cells, overexpression of cyclin B1 had no effect on cell cycle progression. Confirmation that reduction of cyclin B1 levels would prolong G2 was provided using antisense oligonucleotides to cyclin B1. These results demonstrate that cyclin B1 levels control the length of the G2 delay following irradiation in HeLa cells but do not exclude additional mechanisms controlling the mitotic delay after irradiation.

Signalling through sIgA on a novel murine B lymphoma.

A novel murine B lymphoma expressing membrane-associated IgA was isolated and used to compare mechanisms of signal transduction by sIgM and sIgA. Like other isotypes so far studied, crosslinking of sIgA by anti-immunoglobulin antibodies stimulates hydrolysis of inositol phospholipids and causes elevation of intracellular free calcium. Furthermore, signals generated through sIgA are coupled to elevation of c-fos proto-oncogene expression. Coupling appears to be through the protein kinase C rather than through the Ca2+ component of sIg signalling as phorbol diester, but the Ca2+ ionophore cannot mediate this effect. Thus these results, coupled with those from earlier studies, show that early signal transduction through surface immunoglobulin appears to be similar regardless of the particular isotype involved in binding ligand.

Relationship of psychological processes during delirium to outcome.

To determine which psychological processes during delirium might correlate with and predict postdelirium psychological outcome, the authors prospectively studied 34 burn patients who became delirious during hospitalization. After the delirium resolved, seven of the 25 survivors had severe psychological symptoms--either depression or posttraumatic stress disorders. During delirium, this outcome group was clinically distinctive: They showed significantly more preoccupation with their trauma and injury, had greater anxiety and fear, and differed in their use of defensive operations. These findings suggest modifying the standard approach to the delirious patient.

Medical students' learning as primary therapists or as participant/observers in a psychiatric clerkship.

The authors assessed two different inpatient models of clinical clerkships in psychiatry on the basis of both an examination assessing amount of learning and a survey of student attitudes. One clerkship model placed the third-year medical student in the role of primary therapist; the other model assigned each student to join a psychiatrist as a participant/observer. No overall difference in objective assessment of learning was found between the two groups of students, and student attitudes generally favored the participant/observer model. These findings suggest that the widespread bias favoring the primary therapist model may not be justified.

Differences between young and aged mice in susceptibility to Friend virus.

Friend virus (FV) is a murine leukemia virus that infects progenitor red blood cells and causes an erythroleukemia in susceptible mouse strains, resulting in splenomegaly. Several genetic loci of the host have been identified that affect erythroleukemia development, differentiation status of target cells and virus replication. Since age may change expression of these loci, age may affect FV disease. To explore this possibility, FV expression in four genetically diverse strains of mice of different ages was examined. Extent of viral replication and of disease were evaluated by measuring spleen focus forming units (SFFU), spleen weight and reverse transcriptase (RT) activity in target organs. Young DBA/2 and (C57BL/6 x DBA/2)F1 mice exhibited a greater level of virus expression than their aged counterparts in all parameters investigated. Young CBA/Ca mice had slightly higher spleen weights and SFFU values than aged CBA/Ca mice, but a definitive age-related change was not observed in the RT activity of the target organs. C57BL/6 mice, which are genetically resistant to the development of FV-induced erythroleukemia, exhibited a limited degree of virus replication that was not effected by the age of the animal. Our results indicate that the age of the mouse, as well as the genetic background, can contribute to the level of susceptibility to FV.

The utility of serial complete blood count monitoring in patients receiving radiation therapy for localized prostate cancer.

PURPOSE: It is standard practice in our department to monitor weekly complete blood counts (CBCs) in patients receiving definitive radiation therapy for prostate cancer. The clinical utility and cost effectiveness of this practice has not been analyzed. METHODS AND MATERIALS: The charts of all prostate cancer patients treated with radiation therapy between January 1994 and July 1996 at the Veterans Administration Hospital, Philadelphia, PA were reviewed. CBC values were available for 89 patients. Patients received a median dose of 68 Gy using a four-field box technique and megavoltage photons. Whole-pelvic radiotherapy followed by a conedown to the prostate was administered to 29 patients. Fifty-nine patients received radiation to the prostate alone or prostate and seminal vesicles. Fifty-seven patients received concurrent hormonal therapy which included luteinizing hormone-releasing hormone (LHRH) agonist, antiandrogens, or both. RESULTS: No patient experienced a drop in their hemoglobin, white blood cells (WBCs), or platelets below critical nadirs (defined as WBC < 2 counts x 1000/mm(3), hemoglobin < 8 g/dl, platelet < 50 counts x 1000/mm(3) 2 in WBCs. In the urban area surrounding the Philadelphia Veterans Administration Medical Center, the cost of obtaining a CBC is approximately $30. However, if staff time is considered, the cost of obtaining a weekly CBC during prostate cancer radiotherapy approached $400 per patient. CONCLUSION: These results suggest that weekly monitoring of CBCs in prostate cancer patients undergoing definitive radiotherapy may not be necessary. We recommend a baseline CBC be performed, and if normal, no other monitoring unless clinically indicated. This strategy would result in a cost savings approaching $30,000 per 100 treated patients. Further research on the cost effectiveness and utility of serial blood tests in patients receiving partial body radiation therapy is needed.

Altered macrophage antigen-presenting cell function following Friend leukemia virus infection.

To investigate the mechanism by which Friend leukemia virus (FV) causes immunosuppression, the ability of peritoneal macrophages to mediate antigen-specific T-cell activation following FV infection was examined. Decreased IL-2 production was observed when antigen-primed T cells were cultured with antigen-pulsed macrophages from mice infected with FV, compared to T cells cultured with macrophages from control mice. Macrophages from FV-infected mice demonstrated decreased phagocytic and pinocytic activity, suggesting that antigen uptake may be impaired in these cells. In addition, FV-infected mice had decreased numbers of MHC class II positive macrophages compared to uninfected controls, as measured by immunofluorescence. The alterations in antigen uptake and class II expression observed in macrophages from FV-infected mice may be the result of infection of these cells by FV, which was demonstrated by in situ hybridization using a FV-specific probe. The ability of FV to infect and modulate the functions of macrophages may account, at least in part, for the immunosuppression observed in FV-infected mice.

Life-sustaining treatment and assisted death choices in depressed older patients.

OBJECTIVES: The major purpose of this study was to examine the effect of depressed mood in older, medically ill, hospitalized patients on their preferences regarding life-sustaining treatments, physician-assisted suicide (PAS), and euthanasia and to determine the degree to which financial constraints affected their choices. DESIGN: Cross-sectional study. SETTING: General medical hospital. PARTICIPANTS: One hundred fifty-eight medically hospitalized, nondemented patients age 60 or older, mean age 74.1 (range 60-94). The sample was divided, based on Center for Epidemiologic Studies-Depression (CES-D) scores, into a depressed group (n = 71) and a nondepressed control group. MEASUREMENTS: Subjects underwent a structured interview evaluating their life-sustaining treatment choices and whether they would accept or refuse PAS or euthanasia under a variety of hypothetical conditions. These choices were reevaluated with the introduction of financial impact. In addition, assessment included measures of depression, suicide, cognition, social support, functioning, and religiosity. RESULTS: Depression was found to be highly associated with acceptance of PAS and euthanasia in most hypothetical clinical scenarios in addition to patients' current condition. Compared with nondepressed people, depressed respondents were 13 times as likely to accept PAS when considering their current condition (95% confidence interval [CI] 1.68-110.98), and over twice as likely to accept PAS when facing a hypothetical terminal illness or coma. Depression alone was weakly associated with life-sustaining treatment choices but, when financial impact was introduced, significantly more depressed subjects refused treatment options they had previously desired than did nondepressed subjects. The presence of suicidal ideation, even passive ideation, was strongly predictive of life-sustaining treatment refusals and increased interest in PAS and euthanasia. Depression's effect on acceptance of PAS was confirmed by logistic regression, which also showed that religious coping was significantly correlated with less interest in PAS in two hypothetical scenarios. CONCLUSION. Depressed subjects and even subjects with subtle, passive suicidal ideation were markedly more interested in PAS and euthanasia than nondepressed subjects in hypothetical situations. Depressed subjects were also particularly vulnerable to rejecting treatments if financial consequences might have resulted.

Mechanisms of caloric restriction affecting aging and disease.

Caloric restriction (CR) appears to affect aging by the inhibition of the specific chronic diseases which occur at increasing frequency with age. A common disease in F-344 rats, granulocytic leukemia, appears to have a window where it is sensitive to the effects of CR. Other diseases, such as pituitary adenomas, appear to have a different relationship to growth in the animal. Additionally, a model for the major disease for a number of long-lived strains of mice, lymphoma, which CR effects by inhibiting the expression of the causative agent, is being developed. Evaluation of the effects of CR on neoplasia, degenerative disease and physiological parameters suggests that the major factors in expression of these diseases is the alteration of growth factors, hormonal status, etc., and that these alterations also affect strain-specific pathologies depending on when they are changed in the life span. Effecting different diseases at different times in the life span, long-term CR, by limiting exposure to endogenous growth factors, altering physiological characteristics, and limiting exposure to food toxicants, inhibits the onset of disease, and its sequela, aging.

Regulation of benzodiazepine prescribing practices: clinical implications.

In an effort to control prescription abuse of benzodiazepines, the New York State Department of Health (DOH) enacted a regulation requiring the use of triplicate prescriptions for these medications. DOH predicted that this regulation would reduce the overall abuse of benzodiazepines and eliminate widescale organized fraud and abuse without any negative impact or reduced availability to patients. Following implementation of the regulation, the authors reviewed all psychiatric emergency room cases and outpatient clinic walk-in evaluations over a 3-month period in an urban medical center and identified 59 cases in which the use of benzodiazepines was a significant presenting problem. Of these, 24 (41%) were judged to be directly related to the new triplicate regulation. In all but one of these cases the patient presented because of symptoms or concerns directly stemming from the refusal by a clinician to continue prescribing a benzodiazepine in a previously established pattern. Typically, abrupt discontinuation of benzodiazepine treatment led to a withdrawal syndrome and/or the unmasking of a previously treated anxiety disorder. In attempting to redress what are essentially criminal substance abuse problems through the regulation of legitimate clinical practice, regulatory agencies may ultimately deprive patients of appropriate, legitimate, and efficacious treatments.