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Biomedical subjects

A Senik

Publications and source records attributed to A Senik.

At least 55 records · Page 3Linked to original sources
PubMed1986

Regulation of immunoglobulin synthesis by human T cell subsets as defined by anti-D44 monoclonal antibody within the CD4+ and CD8+ subpopulations.

In our previous paper, we demonstrated that anti-D44 MAb can, in the presence of complement, eliminate all the allocytotoxicity generated during a mixed lymphocyte reaction without affecting the alloproliferative response. As approximately 70% of CD4+ cells and 30% of CD8+ will be stained with anti-D44 MAb, we researched the functional role of the D44+ and D44- cells in each of these T cell subsets in the PWM-induced antibody response. We found that most of the helper activity for immunoglobulin (Ig) synthesis was mediated by CD4+ D44+ lymphocytes and that virtually all the suppressive activity was mediated by CD8+ D44- lymphocytes. Surprisingly enough, we noticed that the low level of Ig synthesis induced in B cells by CD4+ D44- lymphocytes could be strongly amplified by the addition of radiosensitive CD8+ lymphocytes, suggesting coexisting opposite immunoregulatory functions within the CD8+ T cell subset. These results, together with previous data, indicate that anti-D44 MAb subdivides T cells into subpopulations with distinct functional repertoires: a CD4+ D44+ helper subpopulation, a CD8+ D44+ cytotoxic subpopulation, and a CD8+ D44- suppressor subpopulation.

Antibodies, Monoclonal↗
PubMed1986

Human monocyte cell line (U937) releases suppressive IgG-binding factor(s).

Fc gamma receptor-bearing U937 cells, when incubated in serum-free buffer, were found to release spontaneously a suppressor material for pokeweed mitogen-drigen IgG synthesis which could be retained on Sepharose 4B-IgG immunosorbents. Immunosorbents coupled with IgM or F (ab')2 fragments of IgG were unable to retain the inhibitory activity of U937-derived material, suggesting a binding specificity for the Fc gamma fragment of IgG. This suppressor material corresponds therefore by definition to an IgG-binding factor (IgG-BF). The mechanism for in vitro suppression of the antibody response by U937-derived IgG-BF was investigated. It did not interfere with cell proliferation and displayed maximum effect when added at day 3 of the culture period. Tested for its effect on IgG, IgM and IgA synthesis, IgG-BF suppressed antibody production following a pattern specific for IgG. Finally gel filtration of the suppressor material gave rise to two peaks of inhibitory activity with an apparent molecular mass comprised between 30 to 40 kDa and 60 to 73 kDa, respectively.

Antibody Formation↗
PubMed1985

A subset of OKT4+ peripheral T cells can generate colonies containing mixed progeny with OKT4+ helper and OKT8+ suppressor cells.

The membrane phenotype of human T cell colony progenitors and that of their clonal progeny was studied for expression of the T4 and T8 determinants. Using clonal culture conditions, the colonies were grown in semi-solid agar medium from peripheral blood cells. Clonality was assessed using the glucose-6-phosphate-dehydrogenase isoenzyme marker. Combination of this marker with the culture of sorted cell fractions allowed us to ascribe the colony progenitors to a subset of OKT4+ lymphocytes. The progeny consisted of the mixture of single OKT4+, single OKT8+ and double OKT4+8+ cells, as determined by double staining. Double staining was performed on mass-harvested colony cells and on individual colonies expanded in liquid culture with fresh interleukin 2. Expression of the OKT8 positivity on colony cells deriving from OKT4+ progenitors required an interaction with radioresistant OKT8+ cells that were co-cultured with these progenitors. Furthermore, the functional capacities of the cell progeny were assayed on the pokeweed mitogen-driven immunoglobulin production by B cells. It was found that OKT4+ colony cells were helper whereas OKT8+ colony cells were suppressor cells. It is concluded that a subset of OKT4+ peripheral blood T lymphocytes can generate colonies containing both helper OKT4+ cells and suppressor OKT8+ cells.

Antibody Formation↗
PubMed1984

Human cytotoxic T lymphocytes (CTL) against Epstein-Barr virus (EBV) infected cells: EBV specificity and involvement of major histocompatibility complex determinants in the lysis exerted by anti-EBV CTL toward HLA-compatible and allogeneic target cells.

Human peripheral blood lymphocytes (PBL), from anti-Epstein-Barr virus (EBV)-seropositive donors, were stimulated by EBV and were shown to be cytotoxic toward autologous, HLA-compatible, and fully allogeneic EBV-transformed target cells. The lysis was not due to natural killer (NK) cells since the target cells used were resistant to lysis by fresh PBL and by virus-stimulated PBL-depleted of AET-SRBC-rosetting T cells (the latter being still fully cytotoxic on K562 NK-susceptible target cells). Conversely only E-rosette-purified (T) lymphocytes killed EBV-transformed HLA-compatible and allogeneic target cells. Moreover, anti-MHC antibodies inhibited the cytotoxicity exerted by EBV-induced cytotoxic T lymphocytes (CTL) on both autologous and allogeneic target cells. Finally the lysis was EBV specific since PHA blasts were not killed and since only EBV-transformed cells could compete for lysis with the EBV-positive target cells. Efficient competition was achieved by EBV-transformed cells autologous or allogeneic to the targets, even when effector and target cells were fully allogeneic. All together, the data suggest that human anti-EBV CTL may recognize nonpolymorphic HLA determinants on the target cells in association with the virus-induced antigens.

Antibodies, Monoclonal↗
PubMed1984

Studies on purification of human gamma interferon: chromatographic behavior of accompanying IL2 and B-cell helper activity.

Gamma interferon (gamma IFN) was produced in human lymphocyte cultures stimulated by PHA. Titers were in the range of 10,000-30,000 U/ml. Crude gamma IFN was adsorbed on silicic acid, from which the antiviral activity was eluted by a buffer containing a high salt concentration and ethylene glycol. This treatment allowed quantitative recovery of gamma IFN with a specific activity of 5 X 10(5)-1 X 10(6) U/mg of proteins. IL2 and B-cell helper activities were adsorbed and eluted from silicic acid together with the antiviral activity. This finding might be of practical interest for the purification of these lymphokines, particularly IL2. Gamma interferon was further purified on Blue Sepharose to a specific activity of 2 X 10(7) U/mg. The resulting preparations still contained IL2 and B cell helper activities. However, taking advantage of the differences in apparent hydrophobicity and in isoelectric point, we were able to dissociate antiviral activity from lymphokines. Such dissociation should facilitate the study of the biological properties of human natural gamma IFN.

Adsorption↗
PubMed1984

Preferential elimination of NK and CTL functions by anti-D44 monoclonal antibody.

Monoclonal antibodies reactive with T cells at various stages of maturation were used in negative selection experiments to study their effects on NK function in the presence of complement. Anti-D47 and anti-A50, respectively, directed against corticothymocytes and mature peripheral E+ cells were without effect. Anti-D66 reactive with an epitope of the T cell E receptor inhibited up to 60% of NK activity. Anti-D44, which primarily recognizes corticothymocytes and 60 to 80% of the E(+)-PBL was found to abrogate NK activity together with alloreactive CTL reactivity but to leave intact most of the MLR and PHA proliferative responses. Therefore D44 appears as a discrete antigen allowing preferential elimination of NK cells and CTL from PBL.

Antibodies, Monoclonal↗
PubMed1982

Inhibition of in vitro natural killer activity by the third component of complement: role for the C3a fragment.

Purified human native third component of complement, C3, was found to inhibit in vitro natural killer (NK) cell cytotoxicity in both mouse and human systems. The effect was dose and time dependent, a 50% inhibition being reached with 190 nM C3 (35 micrograms/ml) added during the NK assay or after a 30-min preincubation of the effector cells with this C3 concentration. C3 was shown to act at the effector-cell population level because pretreatment of the target cells did not modify the NK lysis. The inhibition was not due to general cytotoxicity nor to cell agglutination. Moreover, another in vitro cytotoxicity system (represented by alloreactive cytotoxic lymphocytes) was not affected by purified C3. Structural analysis of the active part of the C3 molecule shows that the C3-induced inhibition is supported by the C3a fragment. Release of carboxyl-terminal arginine residue by carboxypeptidase B, converting C3a into des-Arg77-C3a, did not alter the inhibitory effect displayed by this fragment. These results suggest that C3a may play an important role in the regulation of NK activity.

Animals↗
PubMed1982

Equivalent decrease of H-2Kk and H-2Dk expression after vaccinia virus infection.

Expression of H-2Kk and H-2Dk molecules was studied by indirect immunofluorescence on vaccinia virus-infected Ls cells (derived from the L929 cell line), using D-23b and ASA-21 monospecific alloantisera, respectively directed against the H-2.23 and H-2.32 private specificities of the H-2k haplotype. Our study demonstrates that the increase in vaccinia virus-induced antigens on the membrane of infected cells (as a function of the multiplicity of infection) is associated with a concomitant decrease in the expression of both H-2Kk and H-2Dk serologically defined private specificities. Absorption experiments of D-23b and ASA-21 sera, using infected or uninfected Ls cells, also indicate that after virus infection, H-2Kk and H-2Dk private specificities are equally altered in their serological expression. We finally show that this alteration consists in a mere quantitative decrease of H-2 molecules, since the cytolytic capacity of a rabbit anti-H-2 serum, specifically reacting against the constant part of the heavy chains of H-2 molecules, was significantly more absorbed by uninfected cells than by infected cells. We conclude that no preferential decrease in the expression of H-2 Kk and H-2 Dk molecules is induced during cell infection by vaccinia virus.

Animals↗
PubMed1980

Separate cytotoxic T lymphocyte subsets recognize the different H-2 specificities.

Using a monolayer adsorption technique, the fine specificity of cytotoxic effector T lymphocytes (CTL) generated against allogeneic or semi-allogeneic H-2 haplotypes was investigated. The results show that: (a) CTL reacting with the private specificity expressed on an H-2.K molecule can be separated from those reacting with the public specificities expressed on the same molecule and (b) the CTL that recognize cross-reacting H-2 determinants (public specificities) can also be separated into several subpopulations. These data support the hypothesis that an allogeneic stimulation induces a large number of independent T cell clones that react with H-2 determinants.

Animals↗
PubMed1980

Study of the mechanism for in vitro activation of mouse NK cells by interferon.

The enhancement of the lytic capacity of mouse splenic 'natural killer' (NK) cells by interferon has been studied in vitro as a model for NK cell differentiation from inactive immediate precursors. We show that the increased cytotoxicity is a function of interferon concentration, and that two stages in the NK cell differentiation pathway can be distinguished. The first, very brief, can be performed at 0 degree C and without protein synthesis and probably corresponds to the fixation of interferon on its cell surface receptors. The second, resulting from the inductive signal given by interferon, proceeds for several hours and requires both RNA and protein synthesis. Our results also indicate that target cells for interferon-induced cytotoxicity are cells with 'null' characteristics, similar to the mature NK cells. Finally, they suggest that no soluble intermediary factor other than interferon is involved in the enhancing of NK cell cytotoxicity.

Animals↗
PubMed1980

Public H-2 specificities are target determinants for alloreactive cytotoxic T lymphocytes.

The specificity of the cross-killing exerted by cytotoxic T lymphocytes (CTL's) generated against H-2 region products was investigated in a 51Cr release assay on a panel of target cells from a number of different H-2 haplotypes. Their pattern of reaction shows that: (1) The target cells, expressing public specificities (H-2.28, H-2.1, H-2.3 or H-2.8) which should, theoretically, be recognized by the CTL's were killed, while those expressing no public specificities, recognized according to the H-2 chart by the CTL's were not killed. (2) The CTL's generated against the H-2.28 specificity expressed on the D region products cross react with target cells expressing this specificity in their K region products and vice versa. The same phenomenon was observed with the H-2.1 specificity. These results provide evidence that public specificities are targets for CTL's. Antiserum reacting against the public specificity recognized by the CTL's was found to block the cross-killing, however, to the same extent as antisera directed against any specificity (private or public) expressed on the same molecule as the target determinant. Finally both the inhibition studies using anti-H-2 antisera and the direct cytotoxic assays showed that the public specificities of the H-2.28 family carried by the H-2.D and H-2.L molecules were recognized by different subpopulations of CTL's.

Animals↗
PubMed1980

Multiple CTL subsets generated by H-2.L locus products stimulation: evidence for an antigenic determinant private to H-2.Ld.

Analysis of the fine specificity of CTL subpopulations raised by an H-2.L locus products stimulation (H-2dm2 anti-H-2d) was performed by absorption experiments by using monolayers of macrophages of H-2m, H-2q, H-2b, and H-2k haplotypes. The results show the existence of four CTL subsets. The pattern of reactivity of three of them could be correlated with that of antibodies present in H-2dm2 anti-H-2d antisera (anti-H-2.64, anti-H-2.65, and anti-H-2.Kk). The fourth CTL subset reacted with a specificity unique to H-2.Ld molecules (a private specificity?), absent on cells from H-2m, H-2q, H-2b, and H-2k haplotypes, and undescribed as yet by serologic methods. These data support the hypothesis that the H-2.L locus products are comparable in their antigenic properties to those of the H-2.K and H-2.D loci.

Absorption↗
PubMed1979

Association between H-2 and vaccinia virus-induced antigens on the surface of infected cells.

The relationship between H-2 molecules and vaccinia virus-induced antigens on the surface of H-2d infected cells was investigated by the differential redistribution method and by the blocking capacity of monospecific anti-H-2 sera on an anti-vaccinia cell-mediated cytotoxicity (CMC). Capping of either H-2K or H-2D molecules upon addition of monospecific and anti-H-2 sera was followed by the complete redistribution of viral antigens, suggesting the formation, on the cel membrane, of complexes of H-2K, H-2D molecules and vaccinia virus-induced antigens. However, not all H-2 molecules were involved in this association since i) free H-2K and H-2D molecules still moved independently on the cell surface, and ii) capping of vaccinia virus-induced antigens failed to induce the redistribution of all the H-2K and H-2D molecules. In addition, either monospecific anti-H-2K or anti-H-2D antiserum was found to exert potent blocking activity on anti-vaccinia CMC, indicating also a close topographical relationship between H-2K, H-2D molecules and vaccinia virus-induced antigens.

Animals↗