PubMed Health⌕ Search

Biomedical subjects

A Cannat

Publications and source records attributed to A Cannat.

At least 19 recordsLinked to original sources
PubMed1993

Thermal stress as an inducer of differentiation of U937 cells.

The individual and combined effects of heat shock, all-trans retinoic acid and 1,25-dihydroxyvitamin D3 on inhibition of cell growth and initiation of differentiation were investigated on U937 human leukemia cells. Incubation of U937 cells at 43 degrees C for 1 h did not affect cell viability but induced a reduction of cell growth and the emergence of a differentiated phenotype, characterized by the acquisition of chemiluminescent responses to various oxidative burst inducers and by the capacity to produce IL-6 in response to bacterial lipopolysaccharide. Heat shock alone, therefore, appears to be an efficient inducer of cell differentiation. In addition, heat shock primed the cells to respond more efficiently to the action of retinoic acid and vitamin D, and amplified the phenotypic changes initiated by pretreatment of U937 cells with these agents.

Calcitriol↗
PubMed1987

Biological properties of a panel of murine monoclonal anti-Brucella antibodies.

Immune sera have previously been shown to play a positive role in immune protection against murine experimental brucellosis. The protective properties of a panel of five anti-Brucella monoclonal antibodies (Mabs) were therefore assessed by estimation of the acceleration of the blood clearance of intravenously inoculated Brucella and of the reduction of splenic infection on Day 7 after infection. Three 'strongly protective', one 'weakly protective' and one 'non-protective' Mabs were identified. As a first step towards the study of the mechanism of this humoral protection, these Mabs were further compared for structural and functional properties such as immunoglobulin isotype, anti-Brucella specificity, anti-Brucella in vitro bacteriostasis, Brucella agglutination and complement fixation when complexed with tyndallized Brucella. No correlation was found between protection and either agglutination or direct bacteriostasis. On the other hand, the results observed suggest that isotypes (and especially the IgG2a isotype) could play an important role in in vivo immuno protection and that complement may be involved. However, the fact that one of the protective Mabs belongs to the IgA isotype, does not cross-react with the others in anti-Brucella epitopic specificity and does not fix complement underlines the probable diversity of the mechanisms involved.

Animals↗
PubMed1985

Brucella fractions behave as nonspecific mitogens and polyclonal B-cell activators for human lymphocytes.

Two lipid-A-free fractions which were extracted from Brucella melitensis and were designated PI and SF stimulated human unsensitized mononuclear cells to proliferate and to secrete immunoglobulins. Both of these effects were observed in cultures of peripheral blood, tonsils, and cord blood lymphocytes. Neither B cells nor T cells alone proliferated in the presence of these fractions, whereas the proliferative response of T cells plus B cells was largely independent of accessory cells. Polyclonal activation was estimated by counting the cells which secreted immunoglobulins of different isotypes into culture supernatants. This phenomenon was strongly T dependent.

Adult↗
PubMed1984

Non-specific stimulation of human B lymphocytes by a Brucella fraction.

PI, a lipid A-free fraction (15) extracted from the cell wall of Brucella melitensis type I M.15 behaves as a non specific mitogen and a polyclonal B-cell activator (PBA) for human unsensitized lymphocytes from subjects with no previous history and no biological stigmata of brucellosis. Both effects may be evidenced, indifferently, in cultures of peripheral blood, tonsils or cord blood lymphocytes. Mitogenicity, estimated by the incorporation of tritiated thymidine is maximal on the 5th and 6th day of culture, for high cellular concentrations and for 10 micrograms/PI/well. PBA activity is estimated by the incidence of Prot. A reverse PFC and by a laser nephelometric measure of immunoglobulins in culture supernatants. The use of ET-rosetting for the preparation of purified and/or reconstituted populations demonstrates the T-dependence of the B cell activating effect of PI. On the other hand adherent cell depletion on Sephadex G 10 columns does not significantly impair these effects. Important individual differences are observed and suggest a genetic control of the level of B responses to this new bacterial PBA. These results are discussed in terms of a comparison of PI with other human PBA and of the interactions between non specific and specific responses of lymphocytes from vaccinated subjects or brucellosis patients.

Antigens, Bacterial↗
PubMed1984

Two sensitive assays for the detection of anti-Brucella antibodies.

A laser-nephelometric assay (LNA), applied to an adapted Wright's agglutination technique and an immunoenzymatic assay (ELISA) on tyndallised and sonicated Brucella are described. Both lead to an increased sensitivity of previous techniques for the detection of anti-Brucella antibodies. This was assessed in a) Brucellosis patients with either Wright and/or IF positive reactions (sero-positive) or Wright and IF negative reactions (sero-negative, ancient brucellosis). Positive results were obtained in all cases with a highly significant increase of the titers observed in "sero-positive" patients. b) Normal subjects with no previous history and no biological stigmata of brucellosis: most sera gave negative results - a very low incidence of weakly positive results were however evidenced. c) Subjects vaccinated with fraction PI: positive results were observed in all cases. They were much earlier detected with LNA or ELISA than with Wright's or IF tests and the ELISA or LNA titers of late "sero-positive" sera were 3 to 36 times higher than Wright's titers. d) Supernatants of anti-Brucella hydridomas: LNA and ELISA were both successfully applied to the screening of such supernatants.

Antibodies, Bacterial↗
PubMed1984

Genetic factors involved in murine resistance to experimental brucellosis.

C57 B1/6 are more resistant than DBA2 mice to IV inoculation of Brucella suis 1330. This difference does not concern the blood clearance of the injected bacteria or the number of infective colonies in the spleen at very early (less than 24 h) or at late (greater than 2 months) stages but the splenic infection at intermediate stages with maximal differences between days 7 and 14. The "resistance" character is inherited by F1 and backcrosses as a partially dominant character with polygenic control and a better expression of resistance factor(s) in females, independently of male-female matings. Association of the "resistance" character with known genetic markers was investigated using (B6 X DB) X DB backcrosses, BALB/B, BALB/c, C3H/eb and C3H/HeJ mice. No correlation of "resistance" with Ig allotypes, the "d" coat colour or the LPS genes was evidenced. On the other hand significant differences in the number of splenic colonies on day 7 were observed according to the H-2 haplotype or the "b" coat colour phenotypes. These results are discussed in terms of a comparison with the genetics of other facultative intracellular bacteria and of the partially common and partially independent genetic regulation of the functional components of anti-Brucella resistance.

Animals↗
PubMed1982

In vitro studies on the adjuvanticity of Brucella fractions.

Two Brucella fractions, the murein-linked fraction PI and the murein-free fraction SF, behave as in vitro adjuvants for primary anti-sheep erythrocyte responses: added to Mishell and Dutton-type cultures of spleen cells from B6/DB F1 mice they significantly enhance the number of direct anti-sheep erythrocyte PFC observed on day 5. They exert both nonspecific, polyclonal activating effects and antigen-dependent specific adjuvanticity. These two functions, however, differ in their dose responses and in their cellular requirements and can therefore be dissociated. Thus, polyclonal activation requires high doses of the "adjuvant fraction," is enhanced by adherent-cell depletion, and is not impaired by T-cell depletion. Specific adjuvanticity, on the other hand, requires lower doses of the adjuvant fractions (very high doses are in fact suppressive) and is T-cell and adherent-cell dependent. Moreover, adjuvanticity can be transferred to unstimulated spleen cells (or restored in adherent-cell-depleted populations) by PI- or SF-stimulated adherent cells or by the filtered supernatants of such cultures; adjuvant-soluble factors are therefore involved in the phenomena of adherent, T- and B-cell cooperation required for the adjuvanticity of Brucella fractions.

Adjuvants, Immunologic↗
PubMed1980

Mitogenic activity of two Brucella fractions for murine B lymphocytes.

Two lipid A-free fractions extracted from Brucella melitensis (fractions PI and SF) were shown to behave as B-cell non-specific mitogens for murine lymphocytes: they stimulated the uptake of tritiated thymidine by normal unsensitized murine splenic lymphocytes, by spleen cells from nude mice and by T-cell depleted but not by T-cell enriched and B-cell-deprived splenic populations. Since depletion of adherent cells leads to a two- to three-fold depression of PI- or SF-induced mitogenic responses these two fractions were shown to require accessory adherent cell participation for an optimal mitogenicity. Moreover they behaved as polyclonal activators for murine spleen cells. These results are discussed in terms of a possible classification of PI and SF amongst other B-cell mitogens and of the respective role of the peptidoglycan and lipoprotein moieties in B-cell activation by Brucella fractions.

Animals↗
PubMed1978

Studies on the immune protection to murine experimental brucellosis conferred by Brucella fractions. I. Positive role of immune serum.

Mouse inoculation with three different phenol-insoluble fractions extracted from Brucella melitensis (fractions 'PI', '4A' and '5') induces an acceleration of the blood clearance of i.v. inoculated live Brucella and a diminution of the rate of multiplication of the injected bacteria in the spleen. Preincubation of the challenge inoculum in immune serum or i.p. injections of immune serum confer a good specific protection to non-immunized hosts. The results observed with fractionated sera suggest that, not only antibodies, but also other serum constituents may participate in the protective activity of immune sera. This discussed in terms of the respective importance of humoral and cellular immunity to Brucella and of the choice of the best preparations for human or animal vaccination.

Animals↗
PubMed1977

Genetic control of antinuclear antibodies in mice infected with Rauscher leukemia virus.

The incidence of antinuclear antibodies after Rauscher leukemia virus inoculation was found to be significantly higher in C57BL/6 than in BALB/c mice and still greater in their F1 hybrids. The relationships among antinuclear antibody incidence, erythroblastic disease, Rauscher leukemia virus production, and the H-2 genotypes were studied in the F1 generation and backcrosses using different virus inocula. The results observed suggest that (a) at least two genes are involved in the control of susceptibility to Rauscher leukemia virus-induced erythroblastosis, one of them probably being H-2 linked, and that (b) a non-H-2-linked gene seems to control, at the same time, induction of antinuclear antibodies, focus-forming virus production in the spleen, and susceptibility to the disease. It can be concluded that C-type viruses play an active role in antinuclear antibody induction.

Animals↗
PubMed1976

Enhancement of murine erythrocyte auto-antibody responses by Rauscher leukemogenic virus and by a weak allogeneic stimulation.

B6/c mice do not develop spontaneous positive direct Coomb's tests (DCT), but they are highly susceptible to the induction of erythrocyte auto-antibodies by immunization with cross reacting rat blood cells (36% positive DCT). Rauscher leukemogenic virus (RLV) does not directly induce DCT in these susceptible mice; neither does the inoculation of parental spleen cells. On the other hand both RLV and allogeneic stimulation by parental spleen cells enhance the incidence of the rat blood cell-induced DCT (up to 75% and 69% respectively). This is discussed in terms of a separate etiology to antinuclear and anti-erythrocyte auto-antibodies and of the possible mechanisms of auto-immune stimulation by oncogenic viruses or allogeneic stimulation.

Animals↗
PubMed1976

Stimulating activity of Brucella fractions in a human lymphocyte transformation test. Correlation with humoral and cellular immunity.

'PI' a phenol-extracted fraction from Brucella melitensis has been used for years in our laboratory for the vaccination of laboratory and agricultural workers considered 'at risk'. In the present work it has been used in vitro, together with another phenol-extracted and peptidoglycan containing fraction (4A) in a lymphocyte transformation test. Correlation between stimulation index, humoral antibodies to Brucella and the cutaneous response to PI have been studied in subjects vaccinated with the PI fraction, in Brucellosis patients and normal controls.

Adult↗