CD34+CD38dim cells in the human thymus can differentiate into T, natural killer, and dendritic cells but are distinct from pluripotent stem cells

Recently we reported that the human thymus contains a minute population of CD34+CD38dim cells that do not express the T-cell lineage markers CD2 and CD5. The phenotype of this population resembled that of CD34+CD38dim cells present in fetal liver, umbilical cord blood, and bone marrow known to be highly enriched for pluripotent hematopoietic stem cells. In this report we tested the hypothesis that the CD34+CD38dim thymocytes constitute the most primitive hematopoietic cells in the thymus using a combination of phenotypic and functional analyses. It was found that in contrast to CD34+CD38dim cells from fetal liver and bone marrow, CD34+CD38dim cells from the thymus express high levels of CD45RA and are negative for Thy-1. These data indicate that the CD34+CD38dim thymocytes are distinct from pluripotent stem cells. CD34+CD38dim thymocytes differentiate into T cells when cocultured with mouse fetal thymic organs. In addition, individual cells in this population can differentiate either to natural killer cells in the presence of stem cell factor (SCF), interleukin-7 (IL-7), and IL-2 or to dendritic cells in the presence of SCF, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor alpha(TNFalpha), indicating that CD34+CD38dim thymocytes contain multi-potential hematopoietic progenitors. To establish which CD34+ fetal liver subpopulation contains the cells that migrate to the thymus, we investigated the T-cell-developing potential of CD34+CD38dim and CD34+CD38+ fetal liver cells and found that the capacity of CD34+ fetal liver cells to differentiate into T cells is restricted to those cells that are CD38dim. Collectively, these findings indicate that cells from the CD34+CD38dim fetal liver cell population migrate to the thymus before upregulating CD38 and committing to the T-cell lineage.

Mechanical perturbation elicits a phenotypic difference between Dictyostelium wild-type cells and cytoskeletal mutants

To determine the specific contribution of cytoskeletal proteins to cellular viscoelasticity we performed rheological experiments with Dictyostelium discoideum wild-type cells (AX2) and mutant cells altered by homologous recombination to lack alpha-actinin (AHR), the ABP120 gelation factor (GHR), or both of these F-actin cross-linking proteins (AGHR). Oscillatory and steady flow measurements of Dictyostelium wild-type cells in a torsion pendulum showed that there is a large elastic component to the viscoelasticity of the cell pellet. Quantitative rheological measurements were performed with an electronic plate-and-cone rheometer, which allowed determination of G', the storage shear modulus, and G", the viscous loss modulus, as a function of time, frequency, and strain, respectively. Whole cell viscoelasticity depends strongly on all three parameters, and comparison of wild-type and mutant strains under identical conditions generally produced significant differences. Especially stress relaxation experiments consistently revealed a clear difference between cells that lacked alpha-actinin as compared with wild-type cells or transformants without ABP120 gelation factor, indicating that alpha-actinin plays an important role in cell elasticity. Direct observation of cells undergoing shear deformation was done by incorporating a small number of AX2 cells expressing the green fluorescent protein of Aequorea victoria and visualizing the strained cell pellet by fluorescence and phase contrast microscopy. These observations confirmed that the shear strain imposed by the rheometer does not injure the cells and that the viscoelastic response of the cell pellet is due to deformation of individual cells.

Development of retrovirally marked human T progenitor cells into mature thymocytes

Retroviral vectors have been used in most human gene therapy trials that have been undertaken. Many of these therapies have focused on the introduction of genes into hematopoietic stem cells with the goal of obtaining expression in the mature T lymphocytic progeny. It has proven difficult to achieve expression in the lymphoid lineage, although several groups have demonstrated low expression of transduced genes in the myeloid lineage. In this study we used an in vitro thymic organ culture in which stem/progenitor cells can develop into T cells and all intermediate stages can be studied and manipulated to investigate the fate of a retrovirally introduced Escherichia coli LacZ gene in this system. Here we show that certain conditions can transduce Jurkat T cells, three different antigen-specific T cell clones and CD34+CD3-CD4-CD8- thymocytes (progenitor T cells) with high (> 80%) efficiency. Moreover, retroviral transduction with the LacZ gene does not inhibit T and NK cell differentiation of progenitor cells in fetal thymic organ cultures (FTOC). The LacZ gene also is functionally expressed at all stages of development, although the expression decreases somewhat during differentiation. This experimental system, combining FTOC and retroviral transduction, provides a genetic tool for the study of human T cell development.

gag- and env-specific serum antibodies in cats after natural and experimental infection with feline immunodeficiency virus

In order to monitor the antibody response to feline immunodeficiency virus (FIV) in cats, following experimental and natural infection, enzyme-linked immunosorbent assays (ELISAs) were developed using recombinant env and gag proteins and p24-specific monoclonal antibodies. It was shown that in experimentally infected cats an env protein-specific antibody response was directly followed by a gag protein-specific response. Furthermore, an ELISA for the detection of env protein-specific serum antibodies proved more sensitive in identifying experimentally and naturally infected cats than ELISAs demonstrating gag protein-specific antibodies. It was concluded that, like in HIV infection of humans, the detection of env protein-specific serum antibodies in addition to gag protein-specific antibodies is not only an important tool in the diagnosis of the infection but also in studies concerning the pathogenesis of the disease.

Induction of feline leukaemia virus-neutralizing antibodies by immunization with synthetic peptides derived from the FeLV env gene

The surface glycoprotein, gp70, of feline leukaemia virus (FeLV) contains sites which are important in inducing neutralizing antibodies. Using synthetic peptides corresponding to nucleotide sequence 729-957 (amino acid sequence 243-319) of FeLV-A/Glasgow-1, the antigenicity and immunogenicity of this part of the viral surface glycoprotein were investigated. The region contains two highly conserved domains separated by a variable region (VR4), when compared with FeLV of subgroups B and C, and an epitope known to be involved in virus neutralization is located in the N-terminal conserved domain. Five murine monoclonal antibodies generated by immunization with virus were found to be directed to this domain and four were virus-neutralizing. Polyclonal mouse, rabbit and cat anti-FeLV antisera, which were virus-neutralizing, were directed to B-cell epitopes in the peptides. To determine if those synthetic peptides could induce neutralizing antibodies, rabbits were immunized with the peptides, singly or in combination. Antibody responses were measured by ELISA for anti-peptide, anti-FeLV and anti-gp70 activity, by immunoblotting, by membrane immunofluorescence and by virus-neutralization tests. Virus-neutralizing antibodies were induced by FeLV gp70 peptides and there was a synergistic effect on antibody production when a combination of peptides covering amino acid sequence 243-319 of FeLV-A was used. In a second experiment, six rabbits and six cats were immunized with a combination of two peptides, which covered the above-defined FeLV gp70 sequence. Comparisons were made of the responses to these peptides incorporated into immunostimulating complexes (ISCOMs) via myristic acid tails, inoculated with 'empty' ISCOMs, or with Al(OH)3. Complete Freund's adjuvant (CFA) had a very strong potentiating effect on the induction of antibodies and immunization with peptides incorporated into ISCOMs was superior to immunization using adjuvants other than CFA. It is very promising that not only in rabbits, but also in the natural host of FeLV, the cat, anti-FeLV gp70 (peptides) antibodies could be induced by FeLV gp70 peptides.

Isolation and partial characterization of infectious molecular clones of feline immunodeficiency virus obtained directly from bone marrow DNA of a naturally infected cat

Replication-competent molecular clones of feline immunodeficiency virus (FIV) were isolated directly from the DNA of bone marrow cells of a naturally FIV-infected cat. After transfection in a feline kidney cell line (CrFK) and subsequent cocultivation with peripheral blood mononuclear cells (PBMC), the viral progeny of the clones was infectious for PBMC but not for CrFK cells. PBMC infected with these clones showed syncytium formation, a decrease in cell viability, and gradual loss of CD4+ cells. The restriction maps of these clones differed from those obtained for previously described molecular clones of FIV derived from cats in the United States. The predicted amino acid sequence similarity of the envelope genes of the two clones was 99.3%, whereas the similarities of the sequences of the clones to those of two molecular clones from the United States, Petaluma and PPR, were 86 and 88%, respectively. Most of the differences between the amino acid sequences of the two clones and those of the clones from the United States were found in five different hypervariable (HV) regions, HV-1 through HV-5. The viral progeny of one of these clones was inoculated into two specific-pathogen-free cats. The animals seroconverted, and the virus could be reisolated from their PBMC.

Allotransplantation of K248 feline mammary carcinoma cell line in cats. A model for monoclonal antibody guided detection and therapy of human breast cancer

In response to the need for appropriate models for monoclonal antibody guided detection and therapy of human breast cancer, we developed an allogeneic host-tumor model by injecting K248C and K248P cells into cats. A comparison between the K248C- and K248P-induced tumors with respect to biological behavior and histological appearance was made throughout the study. Allotransplantation of tumor cells was performed both in newborn cats and fetal cats between days 42 and 51 of gestation, but only tumor cells injected by the latter approach resulted in tumor growth in all animals injected. Both tumor cell lines gave rise to progressively growing tumors at the site of injection, metastatic spread of tumor cells to various organs, and death from progression 2-4 months after birth. The predominant histological appearance of the K248C and K248P allografts resembled the cribriform and tubulo-papillary growth patterns, respectively, of the original tumor from which the two cell lines were derived. Autopsy of 1-day kittens showed that metastasis started already in the fetus in the short period between injection of tumor cells and birth. Three predominant patterns of metastases were identified: the pulmonary/pleural type, the abdominal type, and the soft tissue type. A lower incidence of metastases was found in bones and brain. The K248C allografts formed significantly more metastases of the abdominal type than K248P tumors (p less than 0.05). No difference in survival was observed between animals with K248C or K248P allografts. The difference in take rate and latency period between K248C and K248P in athymic mice does not seem to be present in the feline host. The similarity of the present model to spontaneous feline and human mammary carcinoma is discussed.

Feline immunodeficiency virus (FIV) infection in the cat as a model for HIV infection in man: FIV-induced impairment of immune function

To assess the value of feline immunodeficiency virus (FIV) infection as a model for human immunodeficiency virus (HIV) infection in man, we studied the impairment of certain immunological functions following natural or experimental FIV infection. Proliferative responses of peripheral blood mononuclear cells (PBMC) from symptomatic and asymptomatic cats after naturally or experimentally acquired FIV infection, induced by activation with the mitogens concanavalin A, pokeweed mitogen, or lipopolysaccharide or by stimulation with human interleukin-2 (IL-2), were significantly lower than the proliferative responses found with PBMC from noninfected control cats. Also IL-2 production levels of mitogen-activated PBMC from naturally infected symptomatic cats were significantly reduced. These data confirm that the pathogenesis of FIV infection in the cat, like HIV infection in man, is characterized by a serious malfunction of the immune system.

Aztreonam for injection (lyophilized): development of an automated solution batching process utilizing volumetric powder feeders

As part of a commitment to fully automate the manufacture of a lyophilized dosage form of Azactam (Aztreonam for Injection), an automated solution batching procedure was developed. The lyophilization process requires solution batching of Aztreonam and L-arginine, the two constituents of the product. To avoid preblending of aztreonam and L-arginine prior to dissolution, a batching process was developed which makes use of two separate volumetric powder feeders. In conjunction with a feedback pH control system, these powder feeders provided for (a) a faster batching process, (b) a tight control of solution pH during batching, (c) a failsafe system to prevent operator error and equipment malfunction. Data are presented correlating bulk densities of various powders with feeder output along with solution pH profiles determined using the manual mode and the automated feedback pH control system.

Control of feline leukaemia virus

Feline leukaemia virus (FeLV) usually occurs in its natural species, the domestic cat. FeLV is also important to human individuals as a comparative model, as it may cause a variety of diseases, some malignant and some benign, such as immunosuppression, which bears a resemblance to AIDS (acquired immune deficiency syndrome) in man. FeLV is transmitted among cats by contagion. The main sources of infection are persistently infected carrier cats which continuously excrete virus. Dissemination of FeLV among cats may be prevented by identifying infected carrier cats and removing them from contact with non-infected cats. Removal programmes using indirect immunofluorescence antibody tests were applied successfully in The Netherlands. The proportion of FeLV-positive cats decreased from 9% in 1974 to approximately 3% in 1985 during such a programme. The results of a removal programme carried out in a catbreeders' society were even better: the incidence of cats positive for FeLV decreased from 11% in 1974 to less than 2% within 4 years. None of the cats tested in this society has been found to be positive for FeLV since 1984. Besides removal programmes, other methods of control, such as pre-exposure treatment, were developed to prevent the spread of FeLV. We attempted to protect kittens against oronasal infection with FeLV by treatment with virus-neutralizing (VN) monoclonal antibodies (MoAbs) directed against an epitope on the viral glycoprotein gp70. However, no protection was achieved. It is unlikely that the amount of VN antibodies, the mode and route of their application or the infectious dose of FeLV used can account for this failure. Other possible explanations for the lack of protective effect are that (i) the restricted epitope specificity of the MoAb preparation used may have led to selection of neutralization-resistant virus mutants, or (ii) other mechanisms than virus neutralization (complement-mediated lysis, antibody-dependent cell cytotoxicity), that may be involved in protection, function less efficiently with MoAb. However, in the light of our finding that an early anti-idiotypic response is observed in all cats following administration of the MoAb preparation, the rapid clearance of anti-FeLV MoAb from the circulation is a more likely explanation. Efforts were further made to develop a vaccine for controlling FeLV infection. The immunostimulating complex vaccine (FeLV-ISCOM vaccine), a subunit vaccine in which FeLV gp70 is presented in a particular manner, looks promising. The protective effect of FeLV-ISCOM vaccine was studied by vaccinating six 8-week-old SPF cats with ISCOM, followed by oronasal challenge with FeLV.(ABSTRACT TRUNCATED AT 400 WORDS)

Serological responses in cats vaccinated with FeLV ISCOM and an inactivated FeLV vaccine

Various approaches have been considered for generation of effective and safe vaccines against retroviruses, including HIV, with limited success. In the present vaccination study, encompassing 137 household cats, we have composed an experimental ISCOM subunit vaccine containing gp70 of feline leukaemia virus (FeLV)--the external glycosylated envelope protein, and the transmembrane protein p15E, with a commercial available inactivated FeLV vaccine (Leukocell). The two vaccines were estimated to contain approximately the same amount of gp70 antigen and the cats were immunized three times according to the recommendations of the commercial vaccine. A control preparation not containing gp70 or p15E was also included. During the observation period of 200 days all cats remained healthy and no virus was isolated during the isolation attempts. The serological responses were measured in ELISA, membrane immunofluorescence (MIF) and virus neutralization (VN) tests. In contrast to the cats in the other groups almost all ISCOM-vaccinated cats responded by seroconversion or increased titres in the three tests. The development of specific antibodies to gp70 and p15E were confirmed in Western blot. These results clearly illustrate the potential of the ISCOM structure for the development of safe and effective vaccines against retroviruses.

Induction of anti-viral immune response by immunization with monoclonal anti-idiotype antibodies directed to private idiotopes

Syngeneic monoclonal anti-idiotypic antibodies were raised against idiotopes on neutralizing monoclonal antibodies with specificity for feline leukemia virus and canine parvovirus. The anti-idiotypic antibodies were shown to recognize paratope-related private idiotopes. Mice were injected with the monoclonal anti-idiotypic antibodies and the sera of these mice were screened for antiviral reactivities. Antibodies to both feline leukemia and canine parvovirus could be induced as determined by ELISA. These results suggest that anti-idiotypic antibodies which detect private idiotopes and thus do not represent internal images of viral antigens may be considered as candidates for the induction of antiviral immunity.

[Prevalence of FTLV (feline T-lymphotropic lentivirus) infections in cats in The Netherlands and in West Germany]

The prevalence in the Netherlands and the Free Republic of Germany (FRG) of the newly discovered retrovirus of cats, which causes an immunodeficiency syndrome in this species and is termed feline T-lymphotropic lentivirus (FTLV), was estimated by conducting a serological survey among cats with different histories of disease. In an enzyme-linked immunosorbent assay (Petcheck, Agritech Trademark, Portland, USA) 265 samples of cats with chronic disease symptoms, and 78 samples of clinically healthy cats in the Netherlands, and 138 samples of cats with chronic disease symptoms in the FRG, were tested for the presence of FTLV-specific antibodies. All these samples had been taken from cats which were negative for FeLV antigen in the immunofluorescence test. In the groups of chronically ill animals 18 (7%) and 6 (4.5%) seropositive animals were found respectively, whereas in the group of clinically healthy cats no seropositive animals could be demonstrated.

[Feline leukemia virus (FeLV) and FeLV-associated diseases in cats: a review]

Feline leukaemia virus (FeLV) usually occurs in its natural species, the domestic cat. FeLV is also important to human individuals as a comparative model, as FeLV may cause a variety of diseases which are partly malignant and partly benign, such as immunosuppression which bears a resemblance to AIDS (acquired immune deficiency syndrome) in man. Although FeLV is a common infective agent, the incidence of disease due to FeLV is much higher in cats kept in closed households in which several of them are present than it is in free-range cats. Consequently, diseases caused by FeLV are frequently diagnosed in pedigree cats which are often maintained in relatively large numbers. FeLV is transmitted among cats by contagion. The main sources of infection are persistantly infected FeLV carrier cats which continuously excrete virus from the mouth and in other secretions. The majority of cats infected with FeLV will produce neutralising antibodies. Cats which are unable to do so, will become permanently infected. The prognosis is bad in these cats: 90 per cent will die within five years. Various techniques are used to detect FeLV. The most common method, the indirect immunofluorescence (IFA) test, is performed on air-dried blood smears. The results of the IFA agree with that are almost completely identical to those of the virus isolation test. Another test is ELISA (enzyme-linked immunosorbent assay), which produces approximately 10 per cent more positive results which are probably due to circulating FeLV antigens. Dissemination of FeLV among cats may be prevented by identifying infected carrier cats and removing them from contact with non-infected cats. Removal programmes using indirect immunofluorescent antibody (IFA) tests were used successfully in the Netherlands. The proportion of FeLV-positive cats decreased from 9 per cent in 1974 to approximately 3 per cent in 1985 during such a removal programme. During the above period, the removal programme was carried out in the society of Dutch cat breeders 'Felikat', the programme being made compulsory on all members of the society. The incidence of cats positive for FeLV decreased from over 11 per cent in 1974 to less than 2 per cent within four years. None of the cats tested in this society was found to be positive for FeLV in 1984 and 1985. Besides removal programmes, other methods of control, such as vaccination, were developed to prevent the spread of FeLV. The FeLV-immunostimulating complex vaccine (FeLV-ISCOM vaccine) a subunit vaccine in which FeLV-gp70 is presented in a particular manner, seems to be promising.

Feline mammary carcinomas as a model for human breast cancer. I. Sensitivity of mammary tumor cells in culture to cytostatic drugs. A preliminary investigation of a predictive test

Feline mammary carcinomas were found to maintain well in short-term cultures. Principally the same types of nuclear DNA frequency distribution histograms were recognized in feline mammary carcinomas as in human mammary carcinomas. However, the more abnormal histograms are less frequent in feline than in human mammary carcinomas. Feline mammary carcinomas appeared, at least in vitro, most sensitive to Doxorubicin and 5-fluorouracil. Preliminary, thymidine incorporation studies indicate both cytotoxic and cytostatic effects of Doxorubicin and 5-FU. Methotrexate was found to stimulate thymidine incorporation.

Post-exposure treatment with monoclonal antibodies in a retrovirus system: failure to protect cats against feline leukemia virus infection with virus neutralizing monoclonal antibodies

We have attempted to protect kittens against oronasal infection with FeLV (strain A/Glasgow-1) by treatment with a mixture of two virus-neutralizing (VN) MAbs (IgGl, K) directed against the same epitope on the viral glycoprotein gp70. Ten SPF 9-week-old kittens were infected on day 0 with 10(6) ffu FeLV and subsequently inoculated i.m. with MAbs every 2 days over a 20-day period at different times after infection. The results clearly show that no protection was achieved. It is unlikely that the amount of VN antibodies, the mode and route of their application or the infectious dose of FeLV used can account for the failure to protect cats against infection. Other possibilities which may explain the lack of protective effect are that the restricted epitope specificity of the MAb preparation used may have led to selection of neutralization-resistant virus mutants, or that other mechanisms than virus neutralization (complement-mediated lysis, antibody-dependent cell cytotoxicity), that may be involved in protection, function less efficiently with MAb. However, in the light of our finding that an early anti-idiotypic response is observed in all cats following administration of the MAb preparation, the rapid clearance of anti-FeLV MAb from the circulation is a more likely explanation. The data presented support our hypothesis that by administration of MAb-as compared to polyclonal antibody-a more vigorous anti-idiotypic response is elicited due to the presentation of only a limited set of idiotopes. This potential drawback of rapid clearance of MAbs as a consequence of an anti-idiotypic response might be overcome by the use of mixtures of MAbs resulting in a more heterogeneous set of idiotypic determinants.

Induction of protective immune response in cats by vaccination with feline leukemia virus iscom

An effective candidate subunit vaccine consisting of the gp 70/85 of feline leukemia virus (FeLV) was prepared by using the immunostimulating complex (iscom) method for the presentation of membrane proteins of enveloped viruses. Two 32-wk-old specific pathogen-free (SPF) cats were immunized with a FeLV iscom vaccine prepared from the supernatant fluid of the FL74 tumor cell line without adjuvant. Both cats developed FeLV serum antibodies, as measured in an enzyme-linked immunosorbent assay (ELISA) and in a virus neutralization test. A proportion of the antibodies were directed to an epitope located on gp70/85, which was shown in competition ELISA with a peroxidase-labeled virus-neutralizing monoclonal antibody to be shared by all three subtypes of FeLV. The protective effect of FeLV iscom was studied by vaccinating six 8-wk-old SPF cats with iscom prepared from cell culture supernatant of another tumor cell line F422, followed by oronasal challenge with 10(6) ffu FeLV-A (strain Glasgow-1). Six unvaccinated cats were also challenged with the same dose of FeLV. The vaccinated cats developed FeLV serum antibodies, some of which were directed to the shared epitope on gp70/85. At 10 wk after challenge, none was viremic, whereas three of the control cats had developed FeLV viremia. The potential of FeLV iscom as a vaccine against FeLV-associated disease in cats, and of iscom vaccines for protection against mammalian retrovirus infections, is discussed.

Induction of protective immune response in cats by vaccination with feline leukemia virus iscom

An effective candidate subunit vaccine consisting of the gp 70/85 of feline leukemia virus (FeLV) was prepared by using the immunostimulating complex (iscom) method for the presentation of membrane proteins of enveloped viruses. Two 32-wk-old specific pathogen-free (SPF) cats were immunized with a FeLV iscom vaccine prepared from the supernatant fluid of the FL74 tumor cell line without adjuvant. Both cats developed FeLV serum antibodies, as measured in an enzyme-linked immunosorbent assay (ELISA) and in a virus neutralization test. A proportion of the antibodies were directed to an epitope located on gp70/85, which was shown in competition ELISA with a peroxidase-labeled virus-neutralizing monoclonal antibody to be shared by all three subtypes of FeLV. The protective effect of FeLV iscom was studied by vaccinating six 8-wk-old SPF cats with iscom prepared from cell culture supernatant of another tumor cell line F422, followed by oronasal challenge with 10(6) ffu FeLV-A (strain Glasgow-1). Six unvaccinated cats were also challenged with the same dose of FeLV. The vaccinated cats developed FeLV serum antibodies, some of which were directed to the shared epitope on gp70/85. At 10 wk after challenge, none was viremic, whereas three of the control cats had developed FeLV viremia. The potential of FeLV iscom as a vaccine against FeLV-associated disease in cats, and of iscom vaccines for protection against mammalian retrovirus infections, is discussed.

Prognostic factors in feline mammary carcinoma

Feline mammary carcinoma and canine mammary cancer were evaluated as models for future experimental therapy. Those tumor characteristics known to be of special prognostic significance in human mammary cancers were tested for their prognostic significance in the cat and were compared with those in the dog. The statistical analysis presented is based on a prospective follow-up study of 202 cats treated surgically by mastectomy and by block dissection. Thirty-five factors (general, anamnestic, clinical and histologic data, and data on therapy) were analyzed for relationships with survival, with local recurrence, and with each other. Of the 17 significant relationships found between survival and the direct factors, only 7 remained significant after correction. The factors that related to survival independently of each other were age, diameter of the primary tumor, presence of tumor-positive lymph nodes as judged by microscopic examination, number of mitotic figures, necrosis of the primary tumor, and histologic verification of completeness of surgical treatment. The value of statistical analysis for use in prospective studies of human mammary cancer is discussed.

A comparison of three methods of feline leukaemia virus diagnosis

Samples of blood from pet cats were examined for evidence of feline leukaemia virus (FeLV) by three techniques: virus isolation, immunofluorescence and an enzyme-linked immunosorbent assay (ELISA) Leukassay F. There was good agreement between the results from virus isolation and immunofluorescence. However, about 30 per cent of cats which were positive for FeLV antigen by ELISA were negative by either of the other tests. The status of most of these cats was unchanged four or 12 weeks later.

Feline mammary tumours and dysplasias. Conclusions based on personal studies and some suggestions for future research

Feline mammary tumours and dysplasias were studied by various methods: morphological, electron-microscopical, immunotlogical and virological. The most important conclusion was that cats with mammary tumours (benign and malignant tumours and lesions, the significance of which is not known so far) may be suitable animal models for the study of certain features of human mammary tumours; for instance, the study of the relationship between particular histological and biological characteristics of mammary carcinoma and the prognosis; the study of the question whether a virus (or viruses) does (do) or does (do) not play a role in the pathogenesis or growth of mammary tumours; the study of the possible presence of specific cellular and/or humoral immunity to mammary tumours and the study of the possible effects of progestogens on the mammary gland. As the study can not be regarded as a self-contained entity, it should be continued; this applies particularly to those parts of the study, that offer the best prospects for comparative investigations.

Animal model of human disease: breast cancer

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Studies on antibodies against feline leukaemia virus (FeLV) in cat sera and rabbit anti-FeLV sera: cross reaction and differences

The indirect immunoferritin technique (IFT) that enables us to distinguish clearly whether an antibody reacts with a virus particle or only with the cell membrane, was used to study 25 cat sera and one rabbit anti-feline leukaemia virus (FeLV) serum using FL-74 cells as target. (1) All sera contained antibodies against FeLV even though 11 of the cats were viraemic at the same time; (2) from the effect of glutaraldehyde fixation of the FL-74 cells on the reaction with cat sera and the results of blocking experiments, it could be concluded that cat sera and rabbit anti-FeLV sera react partly with different antigenic specificities of FeLV, partly with the same antigens; and (3) the indirect membrane immunofluorescence test using FL-74 cells as target is not a good test to detect the presence of antibodies against feline oncornavirus-associated cell membrane antigen (FOCMA) because FL-74 cells produce a large quantity of FeLV and the fluorescence measured could be from antibodies against FeLV.

[Control of lymphosarcoma or leukaemia in cats and of feline leukaemia virus (author's transl)]

A removal programme, specially designed for catteries or multiple cat households, to reduce the incidence of lymphosarcoma or leukaemia in cats and the spread of feline leukaemia virus (FeLV), is discussed. This removal programme includes annual testing of male stud cats, testing all contacts of FeLV-positive cats they had during the past two years, testing cats imported from abroad and isolation--or, if this is not possible, euthanasia--of cats found to be positive for FeLV-antigen. To detect the FeLV-antigen a simple indirect fluorescent antibody technique (FAT) was used to detect FeLV-antigen. During a period of four years, the following results were obtained when a removal programme was carried out by a large cat breeders' association in the Netherlands. The proportion of catteries, in which FeLV-positive cats were found to be present, decreased from 11.5 per cent in the former half of 1974 to 2.1 per cent in the latter half of 1977. The proportion of FeLV-positive cats and male studs decreased from 4.9 per cent to 1.2 per cent and from 5.9 per cent to 1.0 per cent respectively during this period. It is concluded that the recommended removal programme is a simple and successful procedure.

Feline malignant mammary tumors. III. Presence of C-particles and intracisternal A-particles and their relationship with feline leukemia virus antigens and RD-114 virus antigens

Thirty-six feline mammary tumors were examined by the electron microscope, and by the indirect immunofluorescence (IFA) test with anti-FeLV and anti-RD-114 serum. In 11 (30.6%) tumors intracisternal A-particles (IAP) were found. One of these tumors contained a few particles with an electron-dense nucleoid in the cisternae of the endoplasmic reticulum. In 7 (19.4%) other tumors C-particles were found and in the remaining 18 (50.0%) no particles at all could be detected. In 11 (30.6%) tumors FeLV antigens and in 20 (55.5%) tumors RD-114 virus antigens were present. In 9 (25%) tumors we found a high (greater than 1/64) and in 11 (30.6%) tumors a low (greater than 1/16 less than or equal to 1/64) titer. There was a good correlation between the presence of C-particles and the demonstration of FeLV-antigen but none between IAP and FeLV antigens. No correlation was found between RD-114 virus antigens and any type of particle. Morphologically, the IAP found in feline mammary tumors were indistinguishable from the IAP present in mammary tumors of some inbred mice strains. The IAP in feline mammary tumors possibly represent an endogenous virus, different from RD-114 virus. The role of these viruses in the etiology of feline mammary tumors is discussed.

[The incidence of lymphosarcoma (leukaemia) and feline leukaemia virus (FeLV) in cats in the Netherlands (author's transl)]

Seven different groups of cats were examined to study the incidence and distribution of feline leukaemia virus (FeLV) in the Netherlands. The indirect fluorescent antibody (IFA) technique was used to detect FeLV antigen. Of the cats with lymphosarcoma (leukaemia), 73.2 per cent and of those with infectious peritonitis, 32.4 per cent were found to be positive for FeLV antigen. Of the sixty-six cats with other tumours, only one, a cat with carcinoma of the mammary gland; was positive for FeLV antigen. Of 557 cats with various lesions, forty-two (7.5 percent) were positive for FeLV antigen. The IFA-test was found to be a useful adjunct in establishing the correct diagnosis. Of all stud cats which had been in contact with FeLV-positive cats, 24.7 percent were positive for FeLV antigen, wheras all those which had not been in contact with these cats, were negative. There was a marked difference between the proportions of FeLV-positive cats in the groups of clinically normal cats which had (20.6 per cent) and which had not (0.4 per cent) been in contact with FeLV-positive cats. Follow-up studies showed that 67.8 percent of the clinically normal, FeLV-positive cats had died from or been sacrificed because of FeLV-associated diseases within twenty months.