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Biomedical subjects

P Vassalli

Publications and source records attributed to P Vassalli.

At least 163 records · Page 9Linked to original sources
PubMed1976

The role of lymphocyte-dependent antibody in kidney transplantation.

The lymphocyte-dependent antibody (LDA) assay has been used in parallel with the microlymphocytotoxicity test detecting complement-dependent antibody (CDA) in 100 cadaver kidney transplant recipients, in order to assess the role of the LDA phenomenon in the rejection of human allografts. In 15 cases, acid eluates were prepared from the kidney graft after rejection or at autopsy and tested in parallel with pre- and post-transplantation sera. The results indicate a marked increase in sensitivity of LDA assay compared with the standard microlymphocytotoxicity test. In 12 patients the pretransplant serum was found retrospectively LDA positive, but CDA negative, using the kidney donor lymphocytes or allogeneic lymphocytes bearing the same incompatible antigen(s) for the recipient as targets. Ten of them lost their graft, mostly during the first month after transplantation. Graft survival was also poor in the 11 patients having both LDA and CDA activity in their pretransplant serum, even when the specificity of the serum did not appear to be directed against antigens shared by the donor. Although it is not clear yet, whether the two assays detect the same or different antibody molecules, it appears that the detection of even a low level of LDA activity before transplantation is associated with a high risk of early transplant failure.

Antibodies↗
PubMed1976

Induction or suppression of B cell proliferation and differentiation by phytohemagglutinin or concanavalin A in mouse spleen cell cultures.

Cultures of mouse spleen cells or various mixtures of mouse T and B cells were stimulated with PHA or Con A, and the T, B, or plasmablast nature of the transformed cells, was determined by immunofluorescence 2 to 4 days later. The lectins enhanced B cell proliferation and plasmablast differentiation ("helper" effect) provided one of the following conditions was fultilled: a) suboptimal doses of lectin were used, b) cultures were performed at low cell concentration, c) cultures were made of spleen cells containing a small percentage of T cells, d) the cultures contained a mixture of T-depleted spleen cells and T cells rendered unable to proliferate by irradiation. In contrast, cultures performed with 1.5 10(6) or more spleen cells/ml and optimal doses of lectin contained almost exclusively T blasts, as did cultures stimulated in the same conditions with both PHA and LPS. This last observation idicates the existence of a lectin-induced "suppressor" effect, since LPS, a B cell mitogen, induces, in the absence of PHA, a marked B cell proliferation and differentiation into plasmablasts. These helper and suppressor effects were entirely mediated by T cells, since they were not observed in spleen cell cultures depleted in T cells by anti-thets + C. Analysis of the cultures by immunofluorescence and radioautography after pulses of 3H-thymidine showed that these antagonistic effects could be related to the number of T blasts present in the culture and to their proliferative behavior. Heoper effect is observed in cultures containing a relatively low number of T blasts (or none in cultures made with irradiated T cells), whereas suppressive effect is observed in cultures containing a high number of T blasts, a large proportion of them having left the proliferative cell cycle. It is proposed that when a critical concentration of T blasts is reached ("saturation density"), further proliferation and differentiation is prevented, resulting in a suppressive effect on the generation of plasmablasts. The helper effect of lectin-activated T cells seems to be exerted on a subpopulation of B cells which was, at least in part, already proliferating in vivo, and to result in a polyclonal IgM plasmablast differentiation.

Animals↗
PubMed1975

Synergistic and suppressive interactions among mouse T lymphocytes in the response to phytohemagglutinin.

A synergistic effect in the proliferative response to phytohemagglutinin (PHA) can be observed in cultures containing a mixture of mouse CBA/Ca lymph node cells (LNC) and syngeneic CBA/T6T6 thymocytes (ThC) when compared to cultures containing only one cell type. This effect was analyzed, at various days of culture and in LNC-ThC mixtures of different ratios, by comparing the origin of the cells in mitosis (detected by caryotypic analysis), the stimulation of DNA synthesis, the number of blasts, and the percentage of blasts labeled after pulses of [3H]thymidine (detected by autoradiography). The following conclusions were reached: (a) ThC are induced to proliferate by the presence of LNC, while they are almost unresponsive to PHA when cultured alone; and (b) the strongest "synergistic" effect is exerted on LNC, whose proliferation is markedly enhanced. Evidence is presented that this last effect is not specific to the presence of ThC, but results from a dilution of LNC which retards the time when the culture reaches a critical concentration of blasts, above which proliferation progressively stops. Thus, conditions of culture allowing the response to PHA of a low concentration of LNC leads to the most prolonged T-cell proliferation. These observations may be relevant to the types of T-cell interactions, "synergistic" or "suppressive," occurring during in vitro or in vivo immune responses.

Animals↗
PubMed1975

Study of the cells proliferating in parent versus F hybrid mixed lymphocyte culture.

Caryotypic analysis of the cells dividing in mouse parent-hybrid MLC showed an F1 hybrid cell proliferation, which varied depending upon the source of lymphoid cells used: strong in spleen MLC (sometimes equal to that of the parental cells), less marked in lymph node cell MLC, and most often absent in MLC between cortisone-resistant (CR) thymocytes. MLC between parental spleen cells and F1 CR thymocytes showed, however, that in certain conditions of culture F thymocytes can also proliferate. Using parental or F1 spleen cells lacking T lymphocytes, it was found that F1 cell proliferation is entirely dependent upon the presence of parental T cells, but does not require the presence of T lymphocytes among the F1 cells. Immunofluorescence analysis of the blasts observed in one-way MLC showed that about 70% of the parental blasts were T blasts, and 25%B blasts (containing a high proportion of plasmablasts); among the F1 blasts, there was also the same percentage of B blasts and plasmablasts, but many of the T blasts bore only small amounts of T-cell antigen (MTLA), and there was also about 20%of unstained blasts, possibly T blasts bearing MTLA in amounts undetectable by immunofluorescence. The possibility is discussed that the F1 responding T cells belong to a subpopulation performing a suppressive function; MLC lacking F1 T cells showed increased [3H] thymidine incorporation. The proliferation and differentiation of parental and F1 B cells may result mainly from an unspecific, "polyclonal" triggering.

Animals↗
PubMed1975

Membrane-bound ribosomes of myeloma cells. I. Preparation of free and membrane-bound ribosomal fractions. Assessment of the methods and properties of the ribosomes.

A cell fractionation procedure is described which allowed, by use of MOPC 21 (P3K) mouse plasmocytoma cells in culture, the separation of the cytoplasmic free and membrane-bound ribosomes in fractions devoid of mutual cross-contamination, and in which the polyribosomal structure was entirely preserved. This was achieved by sedimentation on a discontinuous sucrose density gradient in which the two ribosome populations migrate in opposite directions. A variety of controls (electron microscopy, labeling of membrane lipids, further repurification of the isolated fractions) provided no evidence of cross-contamination of these populations. However, when an excess of free 60S or 40S subunits, labeled with a different isotope, was added to the cytoplasmic extract before fractionation, the possibility of a small amount of trapping and/or adsorption of free ribosomal particles by the membrane fraction was detected, especially in the case of the 60S subunits; this could be entirely prevented by the use of sucrose gradients containing 0.15 M KC1. EDTA treatment of the membrane fraction detached almost all the 40S subunits, and about 70% of the 60S subunits. 0.5 M KC1 detached only 10% of the ribosomal particles, which consist of the native 60S subunits and the monoribosomes, i.e. the bound particles inactive in protein synthesis. Analysis in CsC1 buoyant density gradients of the free and membrane-bound polyribosomes and of their derived 60S and 40S ribosomal subunits showed that the free and membrane-bound ribosomal particles have similar densities.

Cell Fractionation↗
PubMed1975

Membrane-bound ribosomes of myeloma cells. II. Kinetic studies on the entry of newly made ribosomal subunits into the free and the membrane-bound ribosomal particles.

The kinetics of appearance of newly made 60S and 40S ribosomal subunits in the free and membrane-bound ribosomal particles of P3K cells were explored by determining the specific radioactivities of their 18S and 28S RNA after various lengths of [3H]uridine pulse. Both 40S and 60S subunits enter free and membrane-bound polyribosomes at comparable rates from the cytoplasmic pool of newly made, free native subunits, the 40S subunits entering the native subunit pool and the polyribosomes slightly earlier than the 60S subunits. At all times, the specific radioactivity of the membrane-bound native 60S subunits was slightly lower than that of the polyribosomal 60S subunits. This indicates that the membrane-bound native 60S subunits are not precursors destined to enter membrane-bound polyribosomes and suggests that they result from the dissociation of ribosomes after chain termination. The results observed also suggest that the membrane-bound native 60S subunits are not reutilized before their release from the membranes, which probably takes place shortly after dissociation from their 40S subunits. The monoribosomes, both free and membrane-bound, had the lowest specific radioactivities in their subunits. Finally, a small amount of newly made native 40S subunits, containing 18S RNA of high specific radioactivity, and apparently also newly made messenger RNA were detected on the membranes. The high turnover of these membrane-bound native 40S subunits suggests that they may represent initiation complexes formed with mRNA which has just reached the membranes and which has not yet given rise to polyribosomes.

Cell Line↗
PubMed1975

Membrane-bound ribosomes of myeloma cells. III. The role of the messenger RNA and the nascent polypeptide chain in the binding of ribosomes to membranes.

Mild ribonuclease treatment of the membrane fraction of P3K cells released three types of membrane-bound ribosomal particles: (a) all the newly made native 40S subunits detected after 2 h of [3H]uridine pulse. Since after a 3-min pulse with [35S]methionine these membrane native subunits appear to contain at least sevenfold more Met-tRNA per particle than the free native subunits, they may all be initiation complexes with mRNA molecules which have just become associated with the membranes; (b) about 50% of the ribosomes present in polyribosomes. Evidence is presented that the released ribosomes carry nascent chains about two and a half to three times shorter than those present on the ribosomes remaining bound to the membranes. It is proposed that in the membrane-bound polyribosomes of P3K cells, only the ribosomes closer to the 3' end of the mRNA molecules are directly bound, while the latest ribosomes to enter the polyribosomal structures are indirectly bound through the mRNA molecules; (c) a small number of 40S subunits of polyribosomal origin, presumably initiation complexes attached at the 5' end of mRNA molecules of polyribosomes. When the P3K cells were incubated with inhibitors acting at different steps of protein synthesis, it was found that puromycin and pactamycin decreased by about 40% the proportion of ribosomes in the membrane fraction, while cycloheximide and anisomycin had no such effect. The ribosomes remaining on the membrane fraction of puromycin-treated cells consisted of a few polyribosomes, and of an accumulation of 80S and 60S particles, which were almost entirely released by high salt treatment of the membranes. The membrane-bound ribosomes found after pactamycin treatment consisted of a few polyribosomes, with a striking accumulation of native 60S subunits and an increased number of native 40S subunits. On the basis of the observations made in this and the preceding papers, a model for the binding of ribosomes to membranes and for the ribosomal cycle on the membranes is proposed. It is suggested that ribosomal subunits exchange between free and membrane-bound polyribosomes through the cytoplasmic pool of free native subunits, and that their entry into membrane-bound ribosomes is mediated by mRNA molecules associated with membranes.

Anisomycin↗
PubMed1975

Experimental focal glomerular lesions elicited by insoluble immune complexes. Ultrastructural and immunofluorescent studies.

Injection of small amounts of ferritin intravenously, into the aorta (above the renal arteries) or into the left renal artery of rabbits hyperimmunized against this protein, results in the formation of circulating, insoluble, antigen-antibody complexes. Some of these complexes localize focally in the renal glomerular capillaries, where they elicit severe lesions. The fate of the complexes and the evolution of the lesions have been followed by immunofluorescent and electron microscopic techniques. Within a few hours, the deposition of complexes in the glomeruli resulted in a massive accumulation of neutrophils platelets, and fibrin, sometimes leading to acute focal necroses of some loops. These lesions were quite similar to those developing in the small dermal vessels during the Arthus reaction. Most of the complexes were rapidly phagocytosed and degraded by neutrophils; swelling and proliferation of endothelial and mesangial cells usually followed the acute damage and contributed to the removal of remaining complexes, cell debris, and fibrin deposits. Later, focal areas of mesangial proliferation and sclerosis were observed, containing large amounts of basement membrane-like material and sometimes of collagen fibrils; synechiae and crescent formation were noted in certain places. These observations suggest that the glomerular localization of very large, poorly soluble or insoluble immune complexes may be responsible for the focal glomerular changes seen in association with subacute bacterial endocarditis, with anaphylactoid purpura, or for some of the most severe lesions developing during chronic immune complex diseases.

Animals↗
PubMed1975

Peyer's patches, gut IgA plasma cells and thymic function: study in nude mice bearing thymic grafts.

Nude mice have poorly developed Peyer's patches with very small or no germinal centers and little lymphoid cell proliferation, and a marked decrease in the number of gut-IgA plasma cells. Thymus grafts, which restore the T lymphocyte population of their lymphoid organs to nearly normal levels, lead to a considerable development of the Peyer's patches and of their germinal centers, assocaited with a considerable increase in gut IgA plasma cells, and in the serum IgA level. These findings are consistent with the postulated relationship between the Peyer's patches germinal center cells and the gut IgA plasma cells, and might help to explain the association of thymic defects, low serum IgA, and lack of intestinal IgA plasma cells observed in some immunodeficiency syndromes of man. Nude mice also have marked decrease in the number of lymphocytes present within the intestinal epithelium. These intraepithelial lymphocytes lymphocytes, which have been shown to be of T nature, are restored to normal numbers after thymus grafting.

Animals↗