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Biomedical subjects

H Snippe

Publications and source records attributed to H Snippe.

16 recordsLinked to original sources
PubMed1992

A vaccine against Semliki Forest virus consisting of a monoclonal anti-idiotypic antibody cross-linked to a protein which contains virus-specific T-helper cell epitopes.

A recombinantly expressed protein, consisting of cro-beta-galactosidase at the N-terminus and amino acid residues 115 to 151 of the E2 membrane of Semliki Forest virus (SFV) at the C-terminus containing two T-helper cell epitopes of SFV, was cross-linked with glutaraldehyde to a noninternal image monoclonal anti-idiotypic antibody (ab2 alpha MAb) able to induce SFV-neutralizing anti-anti-idiotypic (ab3) antibodies in BALB/c mice. This vaccine, which might potentially induce SFV-specific T-helper cell memory, established in BALB/c mice a state of protective immunity against virulent SFV within 10 days of immunization. A steady rise in serum neutralization titre occurred from day 7 to day 28 after primary anti-idiotypic immunization, levelling off thereafter. In primarily immunized mice significant rises of serum neutralization titres, which could be indicative for an operational T-helper cell memory, were not observed after challenge on day 35 with virulent SFV. The results suggest that SFV is neutralized by ab3 antibodies shortly after challenge, preventing, thereby, virus multiplication to levels sufficient to provoke a measurable booster response.

Animals↗
PubMed1992

Immunogenicity and vaccine efficacy of synthetic peptides containing Semliki Forest virus B and T cell epitopes.

A synthetic peptide that contains a Semliki Forest virus (SFV) B cell epitope, located at amino acid positions 240 to 255 of the E2 protein, and an SFV T helper (Th) cell epitope, located at positions 137 to 151 of the E2 protein, evoked high titres of SFV-reactive antibodies in H-2d mice. Although the peptide-induced antibodies did not neutralize SFV in vitro, 70 to 100% of the peptide-immunized mice were protected against SFV, even when viral challenge was presented 4 months after immunization. The protection could be transferred by anti-peptide serum, indicating that antibodies were responsible for the protection. When the Th cell epitope of this protective peptide was replaced by an influenza virus Th cell epitope or by another SFV Th cell epitope, the resulting peptides induced lower non-neutralizing SFV-reactive antibody titres and protected a correspondingly lower percentage of mice (50% and 30%, respectively). A peptide with the same Th cell epitope as the best protective peptide but with a less effective SFV B cell epitope protected only 33% of the mice. These results indicate that protection against SFV by a synthetic peptide is primarily dependent on its ability to induce adequate amounts of antibodies with relevant specificity and sufficient affinity; the ability to induce a relevant (SFV-specific) T memory response played only a minor role in protection.

Amino Acid Sequence↗
PubMed1992

A delayed-type hypersensitivity-inducing T-cell epitope of Semliki Forest virus mediates effective T-helper activity for antibody production.

The rational development of peptide vaccines requires the identification of both B- and T-cell epitopes. In this study, potential T-helper cell epitopes of Semliki Forest virus (SFV) were identified on the basis of their ability to induce delayed-type hypersensitivity (DTH) in mice using recombinant SFV fragments produced as hybrid proteins with beta-galactosidase in Escherichia coli and synthetic peptides coupled to beta-galactosidase. Although the tested fragments spanned almost the entire amino acid sequence of the structural proteins of SFV, only one DTH-inducing region (located between amino acid 137 and 151 of the SFV E2 membrane protein) was identified. Peptides containing this E2 region stimulated lymph node cells from SFV-primed mice in vitro. The ability of the identified T-cell epitope to induce a specific T-helper response in mice was evaluated using synthetic peptides that contained combinations of the DTH-inducing region and different previously identified linear B-cell epitopes of E2. These peptides proved able to induce an antipeptide IgG response in mice in an H-2d-restricted fashion. One of the peptides was also able to induce high titres of IgG reactive with SFV-infected cells and protected 70-100% of the peptide-immunized mice after challenge with virulent SFV. Our findings suggest that DTH and T-helper activity are mediated by different doses of the same T-cell epitope.

Animals↗
PubMed1979

Regulation of the immune response by macrophages.

Regulation of the immune response by macrophages was studied with cellular resistance to Listeria monocytogenes as parameter. The use of agents which suppress macrophage activity during the induction-phase of immunity enabled the induction of protective immunity with killed listeria. Fractionation of the cell content of listeria yielded an RNA'se sensitive fraction which in a dose of 300 ng and in combination with the cationic surfactant dimethyl dioctadecyl ammonium bromide induced protective immunity against listeria.

Adjuvants, Immunologic↗
PubMed1979

Characterization of immunogenic properties of haptenated liposomal model membranes in mice. I. Thymus independence of the antigen.

This paper describes a rather simple coupling method for tripeptide enlarged haptens to phosphatidylethanolamine (PE) and the incorporation of these conjugates into liposomal model membranes (haptenated liposomes). These haptenated liposomes evoke a hapten-specific humoral immune response in mice. The magnitude of the response as measured by the appearance of direct plaque forming cells in the spleen is dependent on the route of immunization and the dose and epitope density of the hapten-PE derivatives. It was not possible to evoke an IgG response after either primary or secondary immunization with haptenated liposomes (as measured by the production of indirect plaques or mercaptoethanol-resistant antibody). These data, in addition to the observations that mice depleted of, or deficient in thymus-derived (T) lymphocytes respond to haptenated liposomes, indicate that these haptenated liposomes are T-cell independent antigens.

Animals↗
PubMed1978

Cellular and molecular requirements for X-linked, hapten-specific B-cell blockade in CBA/N mice.

CBA/N mice, a mutant CBA subline, harbor an X-linked B-cell defect which prevents them from mounting immune responses to certain thymic-independent antigens such as pneumococcal polysaccharides and haptenated-Ficoll derivatives. These mice and the hybrid male progeny of CBA/N females are also exquisitely sensitive to a hapten-specific blockade of their otherwise adequate immune responses to thymic-dependent antigens such as N-2,4-dinitrophenylated-hemocyanin (DNP-KLH). As little as 10 ng of a DNP-Ficoll conjugate given 2 h before immunization with a 5,000-fold greater dosage of DNP-KLH, virtually abolishes the 4th-day direct plaque-forming cell (PFC) response specific for DNP. Responding hybrid (CBA/N x C3H/HeN) female mice are resistant to such blockade even at DNP-Ficoll dosages increased by three orders of magnitude. The DNP hapten and Ficoll must be chemically joined for this blocking effect to occur, and increasing the hapten derivatization of Ficoll increases its blockade-invoking capacity. Significant blockade can be produced by administering DNP-Ficoll as early as 4 days before or as late as 4 h after immunization with DNP-KLH. All currently available data point to the defective B cell as the target of this hapten-polysaccharide-mediated blockade. Mice bearing B memory cells, however, are refractory to such blockade. In addition, DNP-Ficoll injections which cause virtually total blockade of 4th-day primary direct PFC responses to DNP-KLH have little or no effect on the development of DNP-reactive B-cell memory measured at either 8 or 30 days. These findings suggest very different blockade susceptibilities for B cells or their precursors at various stages of differentiative development. Our findings also lead to the formulation of testable hypotheses regarding the mechanism of this selective B-cell blockade phenomenon.

Animals↗
PubMed1978

Effects of cyclophosphamide on the in vivo response of outbred athymic (nude) mice to a thymus-independent antigen (DNP-AGG-Ficoll).

Both nude mice (nu/nu) and their heterozygous littermates (nu/+) were injected with a single IP dose of 300 mg cyclophosphamide (CY)/kg. CY is a known immunosuppressive agent, which affects primarily B lymphocytes. Immunization with the thymus independent antigen DNP-AGG59-Ficoll after CY treatment disclosed that restoration of the primary direct PFC response occurred more rapidly in nude mice than in nu/+ mice. However in these same experiments, the primary indirect PFC response, recovered earlier in nu/+ mice than in nude mice. After CY treatment, secondary indirect PFC responses were delayed in both nude and nu/+ mice, but the greatest effect was seen in nude mice. The data suggest that the presence of T cells has little if any influence on the recovery capacity of those B cells which are destined to become direct PFC. However the recovery of B cells which are destined to produce indirect PFC responses is facilitated by the presence of T cells.

Animals↗
PubMed1978

Specificity of murine delayed-type hypersensitivity to conjugates of large or small haptens on protein carriers bearing lipid groups.

Delayed-type hypersensitivity (DH) in the mouse was provoked with different hapten-carrier complexes mixed with the cationic, surface-active lipid, dimethyl dioctadecyl ammonium bromide (DDA). DH was measured as footpad swelling. Conjugates of bovine serum albumin (BSA) with the small haptens dinitrophenyl (DNP), 'arsonate' (ARS) and 'sulphonate' (SULPH) served to generate strong DH reactions towards the homologous antigen. Insertion of a tripeptide spacer between the hapten and carrier resulted in lower DH reactivity. Optimal dosages and optimal time intervals between sensitization and DH elicitation were determined for the enlarged hapten-carrier complexes. Cyclophosphamide (CY) treatment, before priming with complexes mixed with DDA, caused a 5-6 day delay in the expression of DH but failed to evoke enhanced DH for any of the antigens tested. A broad array of cross reactions between small and enlarged hapten-carrier complexes showed a relative lack of specificity in these DH responses. The results are compared with others reported in the literature and are explained mainly by the effects of electrostatically bound lipid groups of DDA in the sensitizing conjugates.

Animals↗
PubMed1977

Dimethyl diotadecyl ammonium bromide as adjuvant for delayed hypersensitivity in mice.

Immunization of mice with antigen mixed with cationic surface active lipid dimethyl dioctadecyl ammonium bromide (DDA) produced delayed type hypersensitivity (DH), measured as a footpad swelling. The DH to sheep red blood cells or dinitrophenyl conjugated with bovine serum albumin (DNP28-BSA) in DDA exceeded the response of the same antigens in Freund's Complete Adjuvant (FCA) significantly. Treatment of mice with CY 8 hr prior to the injection of antigen in FCA or DDA resulted in delay of the onset of footpad swelling past day 5 and in elimination of the differences in the response due to the adjuvants. Immunization with carrier or hapten-carrier complexes with different epitope density in DDA and elicitation with the homologous and heterologous antigens revealed that the DH was DNP-specific. In vivo priming with DNP28-BSA in DDA and in vitro stimulation with the same antigen resulted in peak responses which were twice as high and were reached almost twice as fast as the earlier found response following immunization in FCA. The advantages of DDA as adjuvant over covalently linked fatty acid chains and over FCA are discussed.

Adjuvants, Immunologic↗
PubMed1976

Bacteriophage MS-2 in the immune response.

Several aspects of the immune response to bacteriophage MS-2 were studied. In thymectomized, irradiated and bone marrow-reconstituted (TXBM) mice, the response was normal when a high dose of antigen was used. With a 50-fold lower dose of MS-2, the response was impaired, indicating a T-cell involvement in antibody formation. More evidence for the (partial) T-cell dependence of MS-2 was obtained from experiments with anti-thymocyte serum or cyclophosphamide-treated mice. (3H)-thymidine incorporation experiments demonstrated that both B and T cells were active upon in vitro stimulation with MS-2. The dose of MS-2 which was able to induce a normal response in TXBM mice, proved to be optimal for both sensitization and elicitation of a DH. It is concluded that MS-2 is a thymus-dependent antigen which is only thymus independent in high doses.

Animals↗
PubMed1976

Effects of cyclophosphamide treatment on the in vitro activity of mouse lymphoid cells after nonspecific and specific stimulation.

A single injection of 300 mg cyclophosphamide (CY)/kg resulted in the mouse in a reduction of the numbers of lymphocytes. The minimal values for spleen and peripheral lymph nodes (PLN) were about 10% and were reached on day 3. The restoration of the spleen started on day 5, while the number of PLN cells was still low on day 21. CY treatment followed by immunization resulted in accelerated recovery and considerably enhanced cell numbers in both organs. Staining with fluorescent antisera revealed that, although the B cell is the main target cell of CY action, in the spleen the total percentage of B and T cells decreases during the period in which the total cell number increases. Immunization diminished the in vitro responsiveness of spleen and PLN cells on phytohemagglutinin (PHA) and concanavalin A (Con A), 7 and 11 days later. The response of PLN cells on lipopolysaccharide (LPS) was, however, strongly enhanced on day 7. CY pretreatment of normal and immunized mice yielded cell populations which behaved identically on nonspecific stimulation in vitro. Starting 5 days after CY, the PHA and Con A responses for spleen cells were impaired, while the initial low R values for PLN cells showed a steady increase. Stimulation of CY spleen cells with LPS resulted in R values of below 1. Specific in vitro stimulation of lymphocytes of immunized mice was performed with sheep red blood cells and a hapten-carrier complex. CY treatment before immunization resulted in an elimination of the in vitro activity on specific stimulation.

Animals↗
PubMed1975

Antibody formation in the mouse induced by hapten-carrier complexes.

The influence of hapten, carrier and their ratio in a complex on T-cell helper stimulation and antibody formation against the dinitrophenyl (DNP) hapten was studied. Complexes of DNP with bovine serum albumin (BSA), bovine gamma-globulin (BGG), isologous mouse immunoglobulin (MIG) and polyvinylpyrrolidone (PVP) as carriers were used. Optimal antibody formation against DNP was obtained with complexes with an intermediate hapten:carrier ratio (DNP 16-minusBSA, DNP 43-minusBGG and DNP 48-MINUSMIG). DNP-PVP complexes were not active either in the primary or in the secondary response. The anti-BSA titre was independent of the number of DNP groups on the complex used for immunization. Inhibition of DNP-plaque formation by spleen cells of immunized mice shows an increase of the inhibitory capacity of the complex with the increase of the hapten-carrier ratio. DNP 16-minusPVP was the only PVP complex which was inhibitory. These results suggest that helper cells involved in the antibody formation against BSA and DNP are reactive with different parts of the complex. Priming of mice with carrier or complex after cyclophosphamide (Cy) treatment followed by a secondary injection with complex 10 days later gave strong indications that there is a greater involvement in stimulation of helper T cells by determinants of the complex (new antigenic determinants (NAD) or NAP-DNP groups) or DNP, than by true BSA determinants. This holds for both the IgM and IgG responses.

Animals↗
PubMed1975

Delayed hypersensitivity in the mouse induced by hapten-carrier complexes.

Delayed hypersensitivity (DH) in the mouse was studied with complexes of dinitrophenyl (DHP) as hapten and bovine serum albumin (BSA), mouse immunoglobulin (MIg) and polyvinylpyrrolidone (PVP) as carrier. Priming with BSA induced strong DH against this carrier, but DN of decreasing strength against complexes with increasing DNP:carrier ratio. Priming with DNP-BSA complexes never resulted in a DH against BSA or DNP 3-minusBSA. Injections of DNP 16-minusBSA and DNP 28-minusBSA induced positive DH which increased with the hapten:carrier ratio of the eliciting antigen. The complexes with an isologous carrier DNP 48-minusMIg or DNP 90-minusMIg induced positive reactions against both complexes but not against the weakly substituted DNP 11-minusMIg. The latter only primed for itself. The importance of the DNP groups as determinant in these DH reactions is stressed by the cross-reactions between DNP-BSA and DNP-MIg complexes and by the induction by DNP 16-minusPVP of positive DH against DNP 28-minusBSA. Cyclophosphamide (Cy) treatment before priming with complexes induced enhanced DH against complexes with sufficient hapten:carrier ratio. Priming with carrier under Cy treatment induced no DH against complexes. All these results indicate that carrier determinants are not involved in the DH against complexes. After priming wtih complexes with a low hapten:carrier ratio the DH is directed against new antigenic determinants (NAD) groups. After priming with complexes with high ratios DH is directed against DNP groups. With adoptive local transfer of spleen cells of primed animals and pretreatment of these cells with anti-thymocyte serum or anti-plasma cell serum and complement it was possible to demonstrate that the T cell was responsible for the DH reactions. The involvement of different determinant groups on the hapten-carrier complexes in immune reactions is discussed.

Animals↗
PubMed1975

Cell co-operation and hapten--carrier complexes.

The co-operation of spleen cells of carrier- and hapten--carrier-primed mice in antibody formation against the hapten part of complexes was studied in 550 rad whole body irradiated mice. Hapten--carrier complexes were prepared with the 2,4-dinitrophenyl group (DNP) as a hapten and heterologous bovine serum albumin (BSA) and isologous mouse immunoglobulin (MIg) as carriers. Priming of donor mice with carrier alone did not prepare for a secondary (IgG) response in the recipients of hapten--carrier. Priming of donors and challenge of recipients with the same hapten--carrier complex resulted in high IgG responses. Whereas donor and recipient immunization with complexes differing in the carrier did not give a secondary response, addition of cells of donors immunized with the carrier of the complex used for challenge, resulted in a secondary response. This was only possible when at least one of the complexes had an intermediate hapten:carrier ratio. Only an IgM or a low IgG response was obtained if both complexes had a high hapten:carrier ratio. Three determinants, namely hapten and carrier groups and new antigenic determinant (NAD), are suggested for antibody formation against hapten--protein complexes. In vivo treatment of donor cells with anti-thymocyte serum (ATS) or anti-plasma cell serum (APCS) and complement (C) suggested that: (1) T-cell epitopes are present on the carrier; (2) DNP groups are B-cell epitopes; (3) NAD and possibly DNP are T-cell epitopes; (4) synergism exists in the collaborative antibody response of B cells recongnizing DNP, T cell recognizing carrier and T cells recognizing NAD. Mitomycin treatment of donor cells was used to test whether cell division was mandatory. While the B cells were sensitive to mitomycin treatment, no effect of this drug was found on the helper activity of T cells.

Animals↗