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G Przewlocki

Publications and source records attributed to G Przewlocki.

12 recordsLinked to original sources
PubMed1998

New sequence-specific human ribonuclease: purification and properties.

A new sequence-specific RNase was isolated from human colon carcinoma T84 cells. The enzyme was purified to electrophoretical homogeneity by pH precipitation, HiTrapSP and Superdex 200 FPLC. The molecular weight of the new enzyme, which we have named RNase T84, is 19 kDa. RNase T84 is an endonuclease which generates 5'-phosphate-terminated products. The new RNase selectively cleaved the phosphodiester bonds at AU or GU steps at the 3' side of A or G and the 5' side of U. 5'AU3' or 5'GU3' is the minimal sequence required for T84 RNase activity, but the rate of cleavage depends on the sequence and/or structure context. Synthetic ribohomopolymers such as poly(A), poly(G), poly(U) and poly(C) were very poorly hydrolysed by T84 enzyme. In contrast, poly(I) and heteroribopolymers poly(A,U) and poly(A,G,U) were good substrates for the new RNase. The activity towards poly(I) was stronger in two colon carcinoma cell lines than in three other epithelial cell lines. Our results show that RNase T84 is a new sequence-specific enzyme whose gene is abundantly expressed in human colon carcinoma cell lines.

Adenocarcinoma↗
PubMed1994

Interferon-gamma downregulates CFTR gene expression in epithelial cells.

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, resulting in defective transepithelial Cl- transport. The regulation of CF gene expression is not fully understood. We report that interferon-gamma (IFN-gamma), but not IFN-alpha or -beta, downregulates CFTR mRNA levels in two colon-derived epithelial cell lines, HT-29 and T84, in a time- and concentration (from 0.1 IU/ml)-dependent manner. IFN-gamma has no effect on the transcription rate of the CFTR gene but reduces CFTR mRNA half-life, indicating that it exerts a posttranscriptional regulation of CFTR expression, at least partly, through destabilization of the transcripts. Cells treated with IFN-gamma contain subnormal amounts of 165-kDa CFTR protein. Assays of adenosine 3',5'-cyclic monophosphate-stimulated 36Cl- efflux and whole cell currents show that CFTR function is diminished in IFN-gamma-treated cells. IFN-gamma and tumor necrosis factor-alpha synergistically reduce CFTR gene expression. Our results suggest that production of these cytokines in response to bacterial infections and inflammatory disorders may alter transmembrane Cl- transport.

Cell Membrane Permeability↗
PubMed1990

The in vivo elimination of CD4+ T cells prevents the induction but not the expression of carrier-induced epitopic suppression.

Injection of mice with an immunogenic dose of carrier (keyhole limpet hemocyanin (KLH)) followed by immunization with hapten-carrier conjugate (TNP-KLH) selectively suppresses anti-hapten antibody response. In this study, the cellular basis of this epitopic suppression and also of the suppression induced by a high dose of carrier were analyzed by in vivo depletion of CD4+ or CD8+ T cell subsets by using mAb. The mAb treatments were performed either at the time of carrier priming or at the time of hapten-carrier immunization. The elimination of CD8+ T cells has not modified the anti-carrier antibody response, whether this treatment was performed at the time of KLH-priming or during TNP-KLH immunization. Moreover, the in vivo treatment with the anti-CD8 mAb did not modify the carrier-induced epitopic suppression induced either by a low immunogenic dose of KLH or by a high dose of this Ag. The elimination of CD4+ T cells at the time of KLH immunization has prevented the induction of a memory response to KLH, clearly establishing that CD4+ T cells are essential in memory B cell development to T-dependent Ag. Moreover, this treatment has totally abrogated the epitopic suppression induced either by low or high dosages of KLH. In contrast, the in vivo elimination of CD4+ T cells after carrier immunization did not abolish the secondary anti-carrier antibody response and did not prevent the expression of epitopic suppression. These data indicate that primed CD4+ T cells are required neither for memory B cell expression nor for the expression of suppression. Finally, once induced, the suppression can be evidenced after in vivo depletion of both primed CD4+ and CD8+ T cells. These data support the view that epitopic suppression is induced through the expansion of carrier-specific B cells and resulted from intramolecular antigenic competition between hapten and carrier epitopes.

Animals↗
PubMed1989

Carrier-induced epitopic suppression is initiated through clonal dominance.

Injection of mice with an immunogenic dose of carrier followed by immunization with hapten-carrier conjugate selectively suppresses anti-hapten antibody response. Previous studies have proposed that this epitopic suppression is related to the induction of carrier-specific Ts cells which in turn could inhibit selectively anti-hapten response. In the present study, we propose that the epitopic suppression is in fact due to clonal dominance. Immunization with a carrier such as tetanus toxoid induces a clonal expansion of carrier-specific B cells, thus decreasing the probability of hapten-specific B cells to react with the Ag. Increasing the density of the TNP-hapten on the conjugate has totally prevented the induction of the epitopic suppression. Moreover, using low hapten-carrier concentrations to challenge carrier-primed mice has enhanced the induction of the suppression. Finally, priming hapten-specific B cells before carrier/hapten-carrier immunization has also abrogated the suppression. The results of these experiments support the view that epitopic suppression is induced through the expansion of the clones specific for the carrier epitopes and resulted from intra-molecular antigenic competition between hapten and carrier epitopes. Based on these findings a regulatory role is proposed for B cells, where through their capacity to process and present antigen, they would exercise a strong influence on the selection of immune responses.

Animals↗
PubMed1989

Alloantigen pretreatment induces a down-regulation of the in vivo subsequent development of cytotoxic T lymphocytes directed against linked alloantigens.

In the present study, we describe a new regulatory system that influences the in vivo development of cytotoxic T lymphocytes (CTL) and that could be related to epitopic suppression. Epitopic suppression has been previously shown to occur when carrier-primed mice are subsequently immunized with a "new" epitope coupled to the priming carrier. The suppression specifically inhibited the antibody response to the "new" epitope without affecting the secondary antibody response to the carrier. In this report, using a carrier/hapten-carrier type of immunization protocol, we have demonstrated that a similar regulatory system could also affect the induction of CTL directed against allogeneic cells. Priming mice with an alloantigen 1 (carrier) inhibits the induction of alloantigen 2 (hapten)-specific cytotoxic responses when the alloantigen 2 is presented in association with the alloantigen 1 on an F1 stimulator cell (hapten-carrier conjugate). This has been demonstrated by the specific decrease of anti-H-2b or anti-H-2d CTL responses generated in C3H/He mice (H-2k) previously primed with, respectively, H-2d or H-2b spleen cells before immunization with F1 (H-2d x b) spleen cells. This suppression of the CTL responses against the second immunizing alloantigen is associated with a strong CTL response against the first priming alloantigen. The induction of the suppression is dependent on the dose of H-2d spleen cells administered before immunization with F1 spleen cells and is not related to antigen elimination since a strong suppression of the CTL response against H-2b antigens is shown following immunization with a mixture of F1 cells and H-2b-bearing cells of H-2d-primed animals.

Animals↗
PubMed1987

A synthetic vaccine constructed by copolymerization of B and T cell determinants.

Synthetic vaccines are based on the identification of short peptide sequences responsible for inducing a protective immune response. These sequences could contain B and/or T cell determinants. In this study, we have examined the recognition by B and T mouse lymphocytes of several synthetic peptides corresponding to regions of a bacterial and two viral proteins. These include a streptococcal S-34 peptide, H(99-121) and two other synthetic hepatitis B virus surface peptides. A lymph node proliferation assay was employed to detect T cell determinants. Limiting dilution analysis was used to estimate the frequency of clonal precursor B cells specific for an antigenic determinant. This study indicates that the synthetic hepatitis B virus surface peptides are recognized by B cells but not by T cells, whereas the S-34 peptide possesses both B and T epitopes. The copolymerization of the B determinant H(99-121) with S-34 has conferred immunogenicity to the H(99-121) peptide. After copolymerization, the synthetic hybrid molecule retained the S-34 T epitope and acquired a new determinant recognized by T cells. These results demonstrate that synthetic vaccines could be constructed by appropriate selection and organization of B and T determinants.

Animals↗
PubMed1986

Production of antibodies recognizing a hepatitis B virus (HBV) surface antigen by administration of murabutide associated to a synthetic pre-S HBV peptide conjugated to a toxoid carrier.

The influence of Murabutide, a muramyl peptide analog, on the response of mice to two synthetic hepatitis B virus antigens was compared with the activity of Al (OH)3 and of FCA. The synthetic peptides represented fragments either of the major component of the hepatitis B surface antigen (HBsAg) or of the pre-S region. They were used either conjugated to toxoid carrier or as a totally synthetic preparation, i.e. copolymerized with a streptococcal peptide. Our results demonstrated that treatment with Murabutide increased the levels of antibodies, modulated their specificity and allowed a better recognition of the natural antigens.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1984

Enhancement by murabutide of the immune response to natural and synthetic hepatitis B surface antigens.

Adjuvant-active murabutide (N-acetylmuramyl-L-alanyl-D-glutamine-alpha-n-butyl ester), devoid of the side effects of muramyl dipeptide (N-acetylmuramyl-L-alanyl-D-isoglutamine), was administered in saline with natural and synthetic hepatitis B surface antigens (HBsAgs). This derivative enhanced the antibody responses against natural HBsAg. The persistence of high antibody titers was the same in the murabutide-treated group as in the alum-treated group. A synergistic enhancement of the antibody was obtained when both adjuvants were administered together. Cell-mediated immunity to HBsAg, tested by the proliferative response of lymph node cells to the antigen, was also shown to be induced in mice treated with alum-associated murabutide. When administered with natural HBsAg, murabutide produced titers of total antibodies as high as did alum but lower titers of specific immunoglobulin E. High levels of antipeptide antibodies were obtained when a synthetic fragment [HBsAg(99-121)] conjugated to a toxoid carrier was administered with murabutide in saline.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1983

Antibody responses elicited by a polyvalent vaccine containing synthetic diphtheric, streptococcal and hepatitis peptides coupled to the same carrier.

Three synthetic peptides copying fragments of the diphtheria toxin, the M protein of the streptococcus type 24 and the hepatitis B virus surface antigen (HBs) have been conjugated together to the tetanus toxoid. This polyvalent vaccine has been administered to mice. High antibody titers were obtained against the three antigens. No cross-reactivity could be observed between them as demonstrated by the ability of each peptide to inhibit only the antibodies against the natural M protein and the synthetic M protein peptide indicated that the avidity of the antibodies raised against a monovalent streptococcal vaccine were identical to those raised following injection of the polyvalent vaccine. Antibodies raised against the polyvalent streptococcal vaccine were also protective as shown by opsonophagocytic assays.

Animals↗
PubMed1982

[Enhancement of the activity of hepatitis B virus vaccine by association with murabutide].

Murabutide (N-acetyl-muramyl-L-alanyl-D-glutamine-alpha-butylester), an MDP analogue, is a potential adjuvant for Human immunization. High levels of specific antibodies were obtained in Mouse and Guinea-Pig following administration with murabutide of low dosages of anti-hepatitis B viral vaccine containing the surface antigen (HBs). The effect of murabutide was enhanced without increasing the level of specific IgE by association with suboptimal dosages of aluminium hydroxide.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMedDate not supplied

Role of major and minor histocompatibility antigens in the suppression of alloreactive cytotoxic responses induced by alloantigen pretreatment.

We have recently shown that priming mice with allogeneic strain A spleen cells before immunization with (A x B)F1 spleen cells strongly suppresses the cytotoxic T-lymphocyte (CTL) response directed against linked strain B alloantigens. This specific decrease in the CTL responses against the second immunizing alloantigen is associated with a high CTL response against the first priming alloantigen. The suppression of CTL responses against the strain B alloantigens is, however, not due to killing of F1 spleen cells by anti-A CTL, since it was observed after immunization of primed mice with a mixture of (A x B)F1 and B cells. In the present study, attempts were made to determine the relative contribution of H-2 and minor histocompatibility background antigens towards induction of suppression. Our results demonstrate that priming and immunizing spleen cells have only to share H-2 antigens in order to induce a downregulation of CTL responses directed against the linked alloantigens. This indicates that immunity against H-2 antigens is sufficient to induce suppression. However, priming against minor histocompatibility antigens also induces suppression, but only if spleen cells used for priming and immunization share H-2 antigens with the recipient strain. Therefore, the suppression can be induced by priming with non-H-2 antigens but is H-2-restricted. This study has also demonstrated that suppression can be induced by intraperitoneal or subcutaneous administration of allogeneic cells.

Animals↗