Interleukin-2 production in vitro: a new approach to the study of rabies vaccine immunogenicity as appraised by testing different glycoprotein presentations

When injected as an immunosome presentation (molecules anchored to preformed liposome), rabies glycoprotein (GP) is capable of protecting animals against rabies either before or after viral infection. The presentation of the GP molecules in the correct form seems to be essential for the induction of antirabies protection. This condition must be taken in account in the making-up of a rabies subunit vaccine. In order to study the relationship between the immune responses induced by the rabies GP and its protective activity, different presentations of the GP were prepared. Purified glycoprotein molecules were associated under different physical forms: liposome-anchored, self-aggregated (rosettes) and associated with the viral lipids (virosomes). These presentations appeared different on electron microscopy. They also exhibited differences in the expression of an immunodominant epitope and in their protective activity. The non-specific immune response, as appraised by interferon production and natural cytotoxicity, was induced at a high level only by the purified viral particles. Specific immune responses (namely virus neutralizing antibody and interleukin-2 production) was induced at high levels only by the viral particle and by the liposome-anchored glycoprotein. A parallelism has previously been established between protection by glycoprotein preparations and interleukin-2 production in primed mice splenocytes. This suggests that the measure of interleukin-2 production in vitro could be used to evaluate the capability of a rabies antigen to induce a T-cell response and to confer protection.

Interleukin 2 increases protection against experimental rabies

Vaccination with either whole inactivated rabies virus or immunosome (rabies glycoprotein anchored on liposomes) induces a high level of interleukin 2 (IL 2) production after in vitro specific stimulation of splenocytes from primed mice (9). On the contrary, infection with a live rabies virus does not specifically induce the production of IL 2: splenocytes from ill mice previously infected with wild rabies virus cannot be specifically stimulated by rabies antigens, whereas they can be non-specifically stimulated by a mitogen (Concanavalin A (Con A]. When injected in mice, exogenous IL 2 (purified rat IL 2 or human recombinant IL 2) exhibits an adjuvant effect on rabies virus vaccine or subunit vaccine tested in a pre-exposure potency test (NIH test). When injected in hamsters, according to a post-exposure potency test (infection with a wild rabies virus followed by vaccination), IL 2 has no adjuvant effect on the rabies vaccine. Nevertheless, when injected alone, IL 2 protects thirty to fifty percent of the infected animals treated (1 hour, 3 and 7 days post-infection) with 10 international units of human recombinant IL 2.

Prevention of low dose streptozotocin induced diabetes by muramyl dipeptide

The objective of the present investigation was to evaluate the effect of the synthetic immunomodulator MDP on an experimentally induced diabetes. It has been previously demonstrated that a single high dose of streptozotocin (STZ) induces hyperglycemia by direct destruction of pancreatic beta-cells. MDP had no effect on the diabetes induced by high dose STZ injection. However, MDP partially protected mice against the toxicity of STZ. In contrast to the first model, repeated low dosages of STZ have been shown to induce hyperglycemia due to autoimmune destruction of beta-cells. Large dosages of MDP given before these low dosages of STZ markedly decreased the diabetogenic effect of STZ. It is proposed that this protection is due to the immunosuppressive activity of MDP.

Structural requirements for the induction of "immunological castration" by linear monomeric LHRH-lys-MDP administered in saline

It was previously shown that "castration" could be obtained in male mice by immunizing them in saline with a conjugate referred to as LHRH-Lys-MDP and containing the decapeptide hypothalamic hormone LHRH covalently linked to the adjuvant glycopeptide MDP-Lys. Since coupling was made using carbodiimide, it could have produced oligomers or isomers as well as monomers. In the present investigation male and female mice were immunized in saline with a linear monomeric MDP linked LHRH molecule obtained by total synthesis. Histological studies showed gonadal alterations in both male and female mice. The study of analogs provided a correlation between the "castrative" activity of LHRH-Lys-MDP and its chemical and antigenic structures. However, because LHRH antibody levels were not very high, mechanisms other than antibody response are discussed. Such totally synthesized molecules including a safe adjuvant could make a clinical use of LHRH immunization possible in endocrine-dependent cancers.

Modulation of carrier-induced epitopic suppression by Bordetella pertussis components and muramyl peptide

Synthetic antigens employed in experimental synthetic vaccines are generally small haptenic peptides. Therefore, effective immunization with these antigens usually requires the use of an immunogenic carrier. Tetanus toxoid has been proposed for use as a carrier in future synthetic vaccines due to its high immunogenicity and acceptance for human use. Previous studies employing standard hapten/carrier systems such as DNP/KLH have demonstrated, however, that an epitope-specific suppression occurs when mice previously primed with carrier are subsequently immunized with an haptenic epitope conjugated to the same carrier. These same studies have shown that Bordetella pertussis vaccine administered at the time of carrier priming abrogates epitopic suppression. In the present investigation, epitopic suppression was studied in a synthetic vaccine model employing tetanus toxoid as a carrier. Results from these studies indicated that mice primed with tetanus toxoid 1 month before immunization with a peptide-tetanus toxoid conjugate exhibited enhanced secondary anti-tetanus toxin responses but decreased anti-peptide responses. Furthermore, injection of pertussis vaccine or purified B. pertussis toxin or endotoxin at the time of carrier priming could block the establishment of epitopic suppression. Administration of B. pertussis components enhanced antibody responses to both the carrier and the synthetic peptides as compared with responses of control animals. In addition, administration of an adjuvant-active nonpyrogenic derivative of muramyl dipeptide. Murabutide, with carrier priming reduced epitopic suppression of anti-peptide responses. B. pertussis toxin or endotoxin administered to mice previously suppressed by carrier priming with the first injection of carrier-peptide conjugate overcame epitopic suppression with resultant titers of anti-peptide antibody equal to or greater than nonsuppressed controls. These results suggest that the use of adjuvants with future synthetic vaccines may contribute the additional advantage of overcoming epitopic suppression, thus permitting the use of common, well-tolerated carrier systems such as tetanus toxoid in synthetic vaccine preparations.

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.

Epitopic suppression in synthetic vaccine models: analysis of the effector mechanisms

The induction of an immune response against synthetic peptides usually requires the use of an immunogenic carrier. The use of tetanus toxoid (TT) has been proposed for this purpose as it is highly immunogenic and has been used extensively in humans. Previous studies have demonstrated that an epitope-specific suppression of IgG antibody responses occurs when mice previously primed with TT are subsequently immunized with SODP, a haptenic epitope linked to TT. In the present investigation, we characterized the effector populations which regulate anti-SODP antibody responses in TT/TT-SODP immunized mice. In vitro studies showed that epitopic suppression did not arise due to nonspecific suppressor phenomena. Coculture experiments demonstrated that epitopic suppression was partially mediated by suppressor T cells which specifically inhibited the anti-hapten but not the anti-carrier antibody response. The majority of these T cells were shown to possess the Lyt-2+ phenotype. Apart from the T suppressor population we demonstrated a deficiency at the B-cell level which contributed to the total suppressive effect. Epitopic suppression, therefore, resulted from the effects of dual specific suppressor mechanisms.

Carrier-induced epitopic suppression, a major issue for future synthetic vaccines

Synthetic antigens have been shown, in experimental models, to induce protective immunity against a variety of pathogens. These studies have demonstrated that, due to their low immunogenicity, these synthetic antigens required conjugation to carrier molecules. Therefore, the choice of appropriate carriers for human immunization by future synthetic vaccines is a major issue. Tetanus toxoid is generally considered to be an effective potential carrier devoid of side-effects. However, the present study performed in mice with two synthetic vaccine models demonstrates that the immune response against the synthetic epitopes conjugated to tetanus toxoid can be suppressed by pre-existing immunity against this same carrier. Because most humans have been exposed to this antigen, this effect may have important implications for the development of synthetic vaccines.

Carrier-induced epitopic suppression, a major issue for future synthetic vaccines

Synthetic antigens have been shown, in experimental models, to induce protective immunity against a variety of pathogens. These studies have demonstrated that, due to their low immunogenicity, these synthetic antigens required conjugation to carrier molecules. Therefore, the choice of appropriate carriers for human immunization by future synthetic vaccines is a major issue. Tetanus toxoid is generally considered to be an effective potential carrier devoid of side-effects. However, the present study performed in mice with two synthetic vaccine models demonstrates that the immune response against the synthetic epitopes conjugated to tetanus toxoid can be suppressed by pre-existing immunity against this same carrier. Because most humans have been exposed to this antigen, this effect may have important implications for the development of synthetic vaccines.

Preparation for hapten help by glucan, muramyl dipeptide, and its L-ala-Glycerol-mycolate derivative

Previously, we reported that one of the factors that determines whether or not an animal will be prepared for hapten help after priming is the type of adjuvant used. The present work was undertaken, therefore, to determine which of a diverse variety of adjuvants or biological response modifiers would be effective. They included Freund's complete (CFA) and incomplete (FICA) adjuvants, particulate glucan, muramyl dipeptide (MDP), and its L-ala-glycerol-mycolate derivative. Help by the azobenzenearsonate (ABA) hapten was measured as the augmentation of the anti-bovine gamma-globulin (BGG) plaque-forming cell (PFC) response to ABA-BGG of mice that had been hapten-primed with ABA conjugated to ovalbumin (OVA). The results showed that FICA was ineffective. MDP was effective but only if administered with FICA during hapten-priming. MDP-L-ala-glycerol-mycolate was effective without any adjuvant but only within a narrow dose range. Particulate glucan was as effective as CFA in preparing mice for hapten help. As the macrophage is the primary cellular target of those biological response modifiers that were effective, we conclude that it plays an important role in the cellular interaction involved in the mediation of hapten help.

Suppression of murine lupus autoantibodies to DNA by administration of muramyl dipeptide and syngeneic anti-DNA IgG

We evaluated the effect of repeated subcutaneous administration of syngeneic anti-DNA IgG and muramyl dipeptide, a synthetic immunoadjuvant, to 6-mo-old (NZB X NZW)F1 female mice. This treatment had profound effects on both idiotype expression and anti-DNA antibody levels of morbid mice. It was also associated with appearance of anti-idiotypic antibodies specific for the injected antibody. These findings suggest that this approach with the use of synthetic immunomodulators and syngeneic antibodies may be of potential use in the management of autoimmune diseases.

Suppression of murine lupus autoantibodies to DNA by administration of muramyl dipeptide and syngeneic anti-DNA IgG

We evaluated the effect of repeated subcutaneous administration of syngeneic anti-DNA IgG and muramyl dipeptide, a synthetic immunoadjuvant, to 6-mo-old (NZB X NZW)F1 female mice. This treatment had profound effects on both idiotype expression and anti-DNA antibody levels of morbid mice. It was also associated with appearance of anti-idiotypic antibodies specific for the injected antibody. These findings suggest that this approach with the use of synthetic immunomodulators and syngeneic antibodies may be of potential use in the management of autoimmune diseases.

Production of porcine interleukin-2 and its biological and antigenic relationships with human interleukin-2

A lymphokine obtained from PHA-stimulated porcine blood leukocytes was found to induce the growth of IL2-dependent murine cells: this factor was therefore considered as the porcine lymphokine analogous to IL2. PHA was found to induce higher amounts of IL2 than Con A. Preculture of porcine PBL or addition of indomethacin enhanced IL2 production, suggesting the existence of a prostaglandin-mediated inhibition of IL2 production in fresh PBL cultures. Porcine IL2 could also promote the growth of activated porcine cells whereas it was inactive on human lymphoblastoid cells. A neutralizing polyclonal anti-human IL2 antiserum was also unable to neutralize porcine IL2. These results indicate therefore, that no biological and antigenic cross-reactivities are demonstrable between human and porcine IL2.

Inhibition of human IL 2 production by MDP and derivatives

In the present study, well-defined immunomodulatory synthetic glycopeptides were used to investigate putative regulatory mechanisms of in vitro IL 2 production by normal human peripheral blood mononuclear cells. MDP (muramyl dipeptide) and two of its structural analogs, murabutide and MDP-DD, were shown to inhibit the in vitro PHA-induced IL 2 production in a majority of normal individuals tested. Involvement of prostaglandins in such an inhibitory effect was suggested by the fact that indomethacin completely abrogated the MDP-induced suppression. There was, however, some evidence indicating that the inhibition induced by the synthetic glycopeptides and that induced by PGE2 were somewhat different. Indeed, although the PGE2-induced suppression of IL 2 production was completely reversed by preirradiation of PBMNC, this was not observed for the MDP-dependent inhibition. In addition, PMA was able to abrogate the suppression induced by MDP, whereas it increased that of PGE2. From these data we propose that at least two independent pathways in the regulation of human IL 2 production exist: a one-signal pathway already described in which PGE2 directly triggers a radiosensitive suppressor T cell subset; and a second pathway with two signals, one given by PGE2 and a second one given by agents such as muramyl peptides. These two signals are required to activate a radioresistant suppressor cell subset.

Inhibition of human IL 2 production by MDP and derivatives

In the present study, well-defined immunomodulatory synthetic glycopeptides were used to investigate putative regulatory mechanisms of in vitro IL 2 production by normal human peripheral blood mononuclear cells. MDP (muramyl dipeptide) and two of its structural analogs, murabutide and MDP-DD, were shown to inhibit the in vitro PHA-induced IL 2 production in a majority of normal individuals tested. Involvement of prostaglandins in such an inhibitory effect was suggested by the fact that indomethacin completely abrogated the MDP-induced suppression. There was, however, some evidence indicating that the inhibition induced by the synthetic glycopeptides and that induced by PGE2 were somewhat different. Indeed, although the PGE2-induced suppression of IL 2 production was completely reversed by preirradiation of PBMNC, this was not observed for the MDP-dependent inhibition. In addition, PMA was able to abrogate the suppression induced by MDP, whereas it increased that of PGE2. From these data we propose that at least two independent pathways in the regulation of human IL 2 production exist: a one-signal pathway already described in which PGE2 directly triggers a radiosensitive suppressor T cell subset; and a second pathway with two signals, one given by PGE2 and a second one given by agents such as muramyl peptides. These two signals are required to activate a radioresistant suppressor cell subset.

Marked enhancement of macrophage activation induced by synthetic muramyl dipeptide (MDP) conjugate using monoclonal anti-MDP antibodies

Activation of peritoneal exudate macrophages of mice to inhibit the in vitro proliferation of tumor target cells was achieved with low concentrations of N-acetyl-L-alanyl-D-isoglutamine (MDP for muramyl dipeptide) conjugated to a synthetic carrier. Addition to the cultures of monoclonal anti-MDP or anti-carrier antibodies renders a thousandfold-smaller concentration of the conjugate highly effective in activating macrophages. This synergistic effect was observed neither with a control monoclonal antibody of different specificity nor with an F(ab)2 fragment of the monoclonal anti-MDP antibody. Other controls, such as addition to the cultures of the carrier alone with its specific monoclonal antibodies, also demonstrated that there exists a requirement for the presence of MDP in the conjugate. The possible uses of such a system as well as the underlying mechanisms are discussed.

In vitro effects of lipopolysaccharides and mycobacterial cell wall components on swine alveolar macrophages

The possible activation of swine alveolar macrophages (AM) by lipopolysaccharides (LPS) and mycobacterial cell wall components such as muramyl dipeptide (MDP) and interphase material (IPM) was investigated. Swine AM were harvested by post mortem lung washings and the following functions were assayed: adherence and spreading in cultures; phagocytosis of ⁵¹Cr-labelled chicken red cells; cytostatic activity against xenogeneic tumour cells (P815 mastocytoma cells); monokine synthesis; interferon and LAF (lymphocyte activating factor or inter-Ieukin-1). Incubation of swine AM with either MDP, LPS or IPM (0·1 μg to 100 μg/ml) for 24 hours did not affect the cell viability but increased their adherence and spreading slightly. Phagocytosis was not markedly modified. Under the same experimental conditions, the unstimulated AM cultures exhibited a strong cytostatic activity which was not modified by these components. No interferon synthesis could be observed in the normal or stimulated AM cultures. In contrast, LAF activity was consistently increased after 48 hours of incubation with LPS, whereas MDP produced this effect only in some experiments.

Effects of intravenous injection of BCG or Freund's complete adjuvant on swine alveolar macrophages

The intravenous injection of killed mycobacteria in oil (Freund's Complete Adjuvant) or BCG produces an accumulation of macrophages in swine alveolar airspaces. The collected alveolar macrophages were studied in vitro: expression of Fc and complement surface receptors, uptake of chicken red blood cells and in vitro spreading were not modified by either treatment, whereas the cytostatic activity of alveolar macrophages decreased following administration of high doses of BCG or Adjuvant. These "treated" cells have a lower thymidine incorporation rate, which suggests that cell accumulation is related to an influx of blood monocytes and not to an in situ cell multiplication.

In vitro effects of lipopolysaccharides and mycobacterial cell wall components on swine alveolar macrophages

The possible activation of swine alveolar macrophages (AM) by lipopolysaccharides (LPS) and mycobacterial cell wall components such as muramyl dipeptide (MDP) and interphase material (IPM) was investigated. Swine AM were harvested by post mortem lung washings and the following functions were assayed: adherence and spreading in cultures; phagocytosis of 51Cr-labelled chicken red cells; cytostatic activity against xenogeneic tumour cells (P815 mastocytoma cells); monokine synthesis; interferon and LAF (lymphocyte activating factor or interleukin-1). Incubation of swine AM with either MDP, LPS or IPM (0.1 micrograms to 100 micrograms/ml) for 24 hours did not affect the cell viability but increased their adherence and spreading slightly. Phagocytosis was not markedly modified. Under the same experimental conditions, the unstimulated AM cultures exhibited a strong cytostatic activity which was not modified by these components. No interferon synthesis could be observed in the normal or stimulated AM cultures. In contrast, LAF activity was consistently increased after 48 hours of incubation with LPS, whereas MDP produced this effect only in some experiments.

Polyclonal antibody-forming cell activation and immunomodulation of the in vitro immune response induced by streptococcal extracellular products

The capacity of three different extracellular streptococcal products to induce polyclonal activation of precursors of plaque-forming cells (PFC) was investigated. The gamma fraction (pI = 4.2), previously shown to be only weakly mitogenic, was the most potent activator of rabbit and mouse immunoglobulin-secreting cells. The polyclonal stimulation induced by the two other fractions (kappa: pI = 4.8 and epsilon: pI = 10.3), shown to be mitogenic in both systems, was only observed in the rabbit system. Using these fractions, the in vitro immunomodulation of the anti-sheep red blood cell immune response was also investigated. Both gamma and epsilon fractions were shown to possess adjuvant properties, whereas the kappa fraction was a suppressor of the specific immune response. It appears, therefore, that the diversified immunological activities observed with extracellular streptococcal products can be dissociated and belong to different entities.

Visceral Leishmania tropica infection of BALB/c mice: cellular analysis of in vitro unresponsiveness to sheep erythrocytes

In mice, infection with Leishmania tropica initially produced a nonspecific enhancement of the immune response to sheep erythrocytes as measured both in vitro and in vivo. Subsequently, the spleen cell responses of susceptible mice (BALB/c) to sheep erythrocytes and T- and B-cell mitogens in vitro decreased dramatically, whereas those of the resistant strain (C57BL/6) returned to normal. Analysis of the spleen cells of infected animals revealed that macrophages (the target cells of Leishmania) were not defective. However, both T- and B-cell-depleted splenocyte populations of infected animals lacked the ability to respond in the presence of their corresponding B- and T-cell-depleted populations of normal spleen cells. It was also observed that the addition of various numbers of Leishmania organisms did not alter the response of normal spleen cells in vitro. The results of cocultures of various ratios of cells from the spleen of infected and normal animals ruled out the possibility of a strong active immunosuppression. The decrease of in vitro response is attributed to the depletion of immunocompetent cells in the spleen of infected mice, which is heavily populated by null cells.