Influence of phospholipid composition on the adjuvanticity and protective efficacy of liposome-encapsulated Leishmania donovani antigens

In this study, we evaluate the effect of phospholipid on the adjuvanicity and protective efficacy of liposome vaccine carriers against visceral leishmaniasis (VL) in a hamster model. Liposomes prepared with distearyol derivative of L-alpha-phosphatidyl choline (DSPC) having liquid crystalline transition temperature (Tc) 54 C were as efficient as dipalmitoyl (DPPC) (Tc 41 C) and dimyristoyl (DMPC) (Tc 23 C) derivatives in their ability to entrap Leishmania donovani membrane antigens (LAg) and to potentiate strong antigen-specific antibody responses. However, whereas LAg in DPPC and DMPC liposomes stimulated inconsistent delayed type hypersensitivity (DTH) responses, strong DTH was observed with LAg in DSPC liposomes. The heightened adjuvant activity of DSPC liposomes corresponded with 95% protection, with almost no protectivity with LAg in DPPC and DMPC liposomes, 4 mo after challenge with L. donovani. These data demonstrate the superiority of DSPC liposomes for formulation of L. donovani vaccine. In addition, they demonstrate a correlation of humoral and cell-mediated immunity with protection against VL in hamsters.     

Protection against Leishmania major infection by oligomannose-coated liposomes

Liposomes coated with neoglycolipids constructed with mannopentaose and dipalmitoylphosphatidylethanolamine (Man5-DPPE) have been shown to induce cellular immunity against antigens encapsulated in the liposomes. To assess whether these neoglycolipid-coated liposomes can elicit protective immune response against challenge infection, effects of immunization with soluble leishmanial antigens encapsulated in the liposomes were evaluated using Leishmania major infection in susceptible BALB/c mice. Intraperitoneal immunization of mice with leishmanial antigens in the Man5-DPPE-coated liposomes significantly suppressed footpad swelling in comparison to the control, non-immunized mice, while progression of the disease was observed in mice administered antigens in uncoated liposomes and those administered soluble antigens alone, as seen with control mice. Similarly, the number of parasites decreased substantially in local lymph nodes of mice immunized with the antigen in the Man5-DPPE-coated liposomes. Protection against L. major infection in the immunized mice also coincided with an elevated ratio of antigen-specific IgG2a/IgG1 antibodies, which is a profile of T helper-type 1-like immune response. Taken together, these results indicate the possibility that Man5-DPPE-coated liposome-encapsulated antigens could serve as a vaccine that triggers protection against infectious disease.     

Vaccination against cutaneous leishmaniasis in a murine model. I. Induction of protective immunity with a soluble extract of promastigotes

BALB/c mice can be protected against a fatal Leishmania major infection by immunization with whole radio-attenuated promastigotes; however, neither the antigens responsible for protection nor the protective immunologic mechanisms have been defined. In this study, the ability of promastigote fractions to elicit similar immunity to that obtained with whole organisms, and the immune responses associated with such protection were analyzed. Intraperitoneal immunization with a soluble, membrane-free parasite extract was found to induce protection against L. major challenge equal to that obtained with whole organisms. Induction of immunity (89% protection in seven experiments) was most effective with 100 micrograms of the soluble leishmanial antigen (SLA) and required concomitant injection of the bacterial adjuvant, Corynebacterium parvum (CP), followed by an i.p. boost of SLA alone 1 wk later. Vaccinated animals exhibited Leishmania-specific cell-mediated immunity, as assessed both by lymphocyte transformation and the production of macrophage-activating factors (MAF). In addition, although SLA + CP-immunized mice failed to exhibit delayed-type hypersensitivity (DTH) before challenge, splenic lymphocytes from these mice could transfer a local DTH reaction to naive recipients. Immunization also induced the production of antibodies against two major metabolically labeled proteins of m.w. 30,000 and 53,000, but failed to stimulate a detectable humoral response against promastigote surface antigens. Thus, these experiments demonstrate that vaccine-induced immunity against cutaneous leishmaniasis is strongly associated with the induction of cell-mediated immunity, but does not require the development of an antibody response to promastigote surface antigens. In addition, these studies establish the feasibility of employing soluble, nonmembrane-derived parasite material as a source of protective immunogens.     

Evaluation of a Liposome-Supplemented Intranasal Influenza Subunit Vaccine in a Murine Model System: Induction of Systemic and Local Mucosal Immunity

Abstract

This study reports on the mucosal immunoadjuvant activity of liposomes in an experimental influenza subunit vaccine administered intranasally (i.n.) to mice. Antibody responses induced by the i.n. liposomal vaccine were compared to those induced by an influenza infection or by subcutaneous (s.c.) injection of subunit antigen alone, the conventional route of human flu vaccination. Negatively charged liposomes, but not positively charged or zwitter-ionic liposomes, coadministered i.n. with influenza subunit antigen, significantly stimulated systemic IgG levels and local antibody responses in pulmonary secretions, relative to the responses upon i.n. administration of subunit antigen alone. I.n. immunization with liposome-supplemented subunit antigen as well as s.c. immunization with subunit antigen alone or infection induced high levels of IgG antibodies in serum and pulmonary secretions, with a preferential induction of IgGl upon immunization and IgG2a upon infection. Both i.n. immunization with liposome-supplemented antigen and infection, but not s.c. immunization with subunit antigen alone, induced local secretion of S-IgA. At the same time, both IgA-and IgG-secreting cells appeared in (he lungs and lung-associated lymph nodes, suggestive of local antibody production. In conclusion, the liposomal adjuvant system, combined with a mucosal administration protocol, provides a promising strategy for induction of both systemic and local antibody responses against influenza virus.     

Prophylactic immunization against experimental leishmaniasis. III. Protection against fatal Leishmania tropica infection induced by irradiated promastigotes involves Lyt-1+2- T cells that do not mediate cutaneous DTH

Protective immunity against fatal L. tropica infection in genetically vulnerable BALB/c mice can be induced by prophylactic immunization with irradiated promastigotes even when heat-killed. Such immunity is adoptively transferable transiently into intact or durably into sub-lethally irradiated (200 or 550 rad) syngeneic recipients by splenic T but not B cells. The effector T cells are of the Lyt-1+2- phenotype, devoid of demonstrable cytotoxic activity. The immune splenic T cell population expresses specific helper activity for antibody synthesis. A causal role for helper T cells in this capacity, however, seems unlikely, because it was shown in the accompanying paper that antibody does not determine the protective immunity against L. tropica. The immunized donors show no detectable cutaneous DTH or its early memory recall in response to live or killed promastigotes or a soluble L. tropica antigen preparation. Spleen, lymph node, and peritoneal exudate cells from protectively immunized donors similarly fail to transfer DTH locally or systemically. These cells also lack demonstrable suppressive activity against the expression or induction of DTH to L. tropica. Thus, protection against L. tropica induced by prophylactic i.v. immunization with irradiated promastigotes appears to be conferred by Lyt-1+2- T cells that are distinguishable from T cells mediating either both DTH and T help, or cytotoxicity.     

Trypanosoma cruzi: predominance of IgG2a in nonspecific humoral response during experimental Chagas' disease.

The kinetic and isotypic pattern of hypergammaglobulinemia has been investigated in C3H/HeJ infected with Trypanosoma cruzi. Hypergammaglobulinemia appeared 14 days postinfection, increased until Day 28 postinfection, and persisted throughout the chronic phase (greater than 60 days of infection). The main isotype secreted was IgG2a, reaching 10-fold the control level. High titers of autoantibodies were found of IgM and IgG subclasses. Isotypic characterization of antibodies against myosin, myelin, and keratin, was performed and determined to be IgG2a subclass in the chronic stage of infection. Specific responses against T. cruzi took place 2 weeks postinfection when the parasitemia was high. Interestingly, parasite-specific response was maximal after 4 weeks of infection and plateaued during the chronic phase when parasites were rare. In contrast to the humoral polyclonal response in the chronic stage, showing a preferential IgG2a pattern, the anti-T. cruzi response consisted of all the different isotypes: IgM, IgG1, IgG3, IgG2a, and IgG2b, throughout the infection. Identical patterns of parasite antigens were recognized by IgG2a and IgG2b antibodies. Few different antigens were identified by the IgG3. Some antigens were recognized by several isotypes, others by only one isotype. With regard to the existence of antigenic cross-reactivities between host and parasite, we designed absorption experiments on parasite-specific immunoadsorbent showing that specific antibodies eluted from the column failed to recognize the natural antigens. These studies suggest that nonspecific and antiparasite-specific responses may be maintained by different regulatory pathways.     

Protective effect of antiganglioside antibodies against experimental Trypanosoma brucei infection in mice

Liposome-associated ganglioside antigens (ganglioside GM1 or bovine brain gangliosides) were prepared to facilitate the potential protective efficacy for Trypanosoma brucei. Mice were immunized with liposome-associated ganglioside GM1 or bovine brain gangliosides intraperitoneally (i.p.). After immunization, significantly higher antigen-specific IgG and IgM antibodies were detected in sera than in the nonimmunized control group. When sera from immunized mice were analyzed for isotype distribution, antigen-specific IgG1, IgG2a, and IgG3 antibody responses were also noted. After immunization, mice were challenged i.p. with 1 x 10(2) cells of T. brucei. Sixty percentage of liposome-associated ganglioside GM1-immunized mice survived the infection, and all the mice immunized with bovine brain gangliosides-containing liposomes survived. However, all control mice died within 7 days after infection. These data demonstrate that liposomes containing ganglioside antigens have the potential usefulness for the induction of a protective immune response against T. brucei infection and suggest the possibility of developing vaccines that may ultimately be used for the prevention of trypanosomiasis.     

Liposomes as a Mucosal Adjuvant System: An Intranasal Liposomal Influenza Subunit Vaccine and the Role of IgA in Nasal Anti-Influenza Immunity

Abstract

Liposomes exhibit potent immunoadjuvant activity in a variety of experimental vaccine formulations. We have investigated the mucosal adjuvant activity of liposomes in an influenza subunit vaccine. Mice were immunized intranasally (I.N.) with the major surface antigen of influenza virus, hemagglutinin (HA), mixed with negatively charged liposomes. Inclusion of the liposomes in the vaccine resulted in a marked stimulation of the serum IgG response against the antigen. In addition, the liposomal preparation, but not the antigen alone, induced a significant secretory IgA (s-IgA) response, not only in the lungs and nasal cavity, but also at the mucosa of the urogenital tract. The adjuvant activity of the liposomes appeared to be independent of a physical association of the antigen with the liposomes: Stimulation of antibody responses was observed even when liposomes and antigen were administered separately in time. Serum IgG and local s-IgA responses to I.N. immunization with the liposomal vaccine were comparable to the corresponding responses induced by an influenza infection. Mice immunized with the liposomal vaccine or mice recovered from an influenza infection were completely protected from (re)infection. Protection from nasal infection was abrogated by treatment of the mice with an anti-IgA antiserum, while anti-IgG had no effect, indicating that s-IgA plays an essential role in nasal anti-influenza immunity.     

Protective immunity induced by systemic and mucosal delivery of DNA vaccine expressing glycoprotein B of pseudorabies virus

A murine model immunized by systemic and mucosal delivery of plasmid DNA vaccine expressing glycoprotein B (pCIgB) of pseudorabies virus (PrV) was used to evaluate both the nature of the induced immunity and protection against a virulent virus. With regard to systemic delivery, the intramuscular (i.m.) immunization with pCIgB induced strong PrV-specific IgG responses in serum but was inefficient in generating a mucosal IgA response. Mucosal delivery through intranasal (i.n.) immunization of pCIgB induced both systemic and mucosal immunity at the distal mucosal site. However, the levels of systemic immunity induced by i.n. immunization were less than those induced by i.m. immunization. Moreover, i.n. genetic transfer of pCIgB appeared to induce Th2-biased immunity compared with systemic delivery, as judged by the ratio of PrV-specific IgG isotypes and Th1- and Th2-type cytokines produced by stimulated T cells. Moreover, the immunity induced by i.n. immunization did not provide effective protection against i.n. challenge of a virulent PrV strain, whereas i.m. immunization produced resistance to viral infection. Therefore, although i.n. immunization was a useful route for inducing mucosal immunity at the virus entry site, i.n. immunization did not provide effective protection against the lethal infection of PrV.     

Identification of novel Leishmania major antigens that elicit IgG2a response in resistant and susceptible mice

Experimental murine models with high, intermediate and low levels of genetically based susceptibility to Leishmania major infection reproduce almost entire spectrum of clinical manifestations of the human disease. There are increasing non-comparative studies on immune responses against isolated antigens of L. major in different murine strains. The aim of the present study was to find out whether there is an antigen that can induce protective immune response in resistant and susceptible murine strains. To do that, crude antigenic extract of procyclic and metacyclic promastigotes of L. major was prepared and subjected to SDS-PAGE electrophoresis. Western-blotting was used to search for antigen(s) capable of raising high antibody level of IgG2a versus IgG1 in the sera of both infected resistant and susceptible strains. Two novel antigens from metacyclic promastigotes of L. major (140 and 152 kDa) were potentially able to induce specific dominant IgG2a responses in BALB/c and C57BL/6 mice. The 2 antigens also reacted with IgG antibody of cutaneous leishmaniasis patients. We confirm that 140 and 152 kDa proteins of L. major promastigotes are inducing IgG production in mice and humans.     

Prophylactic immunization against experimental leishmaniasis. II. Further characterization of the protective immunity against fatal Leishmania tropica infection induced by irradiated promastigotes

The genetic vulnerability of BALB/c mice to Leishmania tropica (L. major) infection renders them incapable of controlling a primary cutaneous lesion that leads to uniformly fatal visceral disease. Potent, long-lasting protection involving both lesion healing and survival can be induced by repeated prophylactic i.v. immunization with gamma-irradiated (150K rad) L. tropica promastigotes. The effect is not dependent on continuing viability or cellular invasiveness of the irradiated parasites because their effective immunogenicity withstands heating at 56 degrees C for 1 hr. Immunity is not stage specific and encompasses both amastigote and promastigote challenges. Similar prophylaxis can be induced by immunization with heterologous irradiated L. donovani promastigotes. Repeated i.v. immunization with irradiated L. tropica promastigotes induces an antibody response in the isotype sequence M leads to G1/G3 leads to G2a/G2b leads to A with substantially higher titres than are found in response to the infection itself. Splenectomy before immunization drastically reduces this antibody response without incurring any impairment of the extent of protection. Passive transfer of large amounts (up to 10 ml) of hyperimmune serum (or isotype fractions thereof) throughout the first 8 wk of infection fails to arrest disease progression during this period. Despite the previously described lack of any detectable cutaneous DTH reactivity, which has hitherto correlated with protective cell-mediated immunity, the results obtained do not support attribution of an alternative causal role to the humoral response.     

Immunogenic dialyzable factor derived from a ribosomal fraction of Salmonella typhimurium III. Analysis of resistance induced by dialyzable factors

Dialyzable factors (DF) were prepared from ribosomal fractions of several organisms including rough mutants of Salmonella typhimurium LT2, salmonella species of different serogroups, other enteric bacteria and gram-positive organisms, and tested for their immunogenicity against S. typhimurium infection in mice. All of them conferred local resistance on mice challenged intramuscularly with S. typhimurium LT2 in the early stage of immunization before the establishment of delayed-type hypersensitivity (DTH) to salmonella antigens. Although DFs of enteric bacteria including rough mutants of S. typhimurium induced DTH to salmonella antigens, only DF of a two-heptose mutant of S. typhimurium LT2 afforded significant mouse protection but others only prolonged the mean time to death. DF of Listeria monocytogenes induced the cross-reacting immunity which afforded the low level of mouse protection as well as an increase in mean time to death without inducing DTH. Passive transfer of anti-O antibody did not enhance the mouse protection provided by each DF. Resistance conferred by DF of S. typhimurium LT2 consisted of two phases: (i) nonspecific macrophage activation resulting in reduction of organisms at the infected site, which became active in the early stage of immunization and (ii) salmonella-specific immunity capable of preventing systemic infection, which became active in the late stage of immunization.     

Conserved metabolic enzymes as vaccine antigens for giardiasis

Giardia lamblia is a leading protozoal cause of diarrheal disease worldwide. Infection is associated with abdominal pain, malabsorption and weight loss, and protracted post-infectious syndromes. A human vaccine is not available against G. lamblia. Prior studies with human and murine immune sera have identified several parasite antigens, including surface proteins and metabolic enzymes with intracellular functions. While surface proteins have demonstrated vaccine potential, they can exhibit significant variation between G. lamblia strains. By comparison, metabolic enzymes show greater conservation but their vaccine potential has not been established. To determine whether such proteins can serve as vaccine candidates, we focused on two enzymes, α-enolase (ENO) and ornithine carbamoyl transferase (OCT), which are involved in glycolysis and arginine metabolism, respectively. We show in a cohort of patients with confirmed giardiasis that both enzymes are immunogenic. Intranasal immunization with either enzyme antigen in mice induced strong systemic IgG1 and IgG2b responses and modest mucosal IgA responses, and a marked 100- to 1,000-fold reduction in peak trophozoite load upon oral G. lamblia challenge. ENO immunization also reduced the extent and duration of cyst excretion. Examination of 44 cytokines showed only minimal intestinal changes in immunized mice, although a modest increase of CCL22 was observed in ENO-immunized mice. Spectral flow cytometry revealed increased numbers and activation state of CD4 T cells in the small intestine and an increase in α4β7-expressing CD4 T cells in mesenteric lymph nodes of ENO-immunized mice. Consistent with a key role of CD4 T cells, immunization of CD4-deficient and Rag-2 deficient mice failed to induce protection, whereas mice lacking IgA were fully protected by immunization, indicating that immunity was CD4 T cell-dependent but IgA-independent. These results demonstrate that conserved metabolic enzymes can be effective vaccine antigens for protection against G. lamblia infection, thereby expanding the repertoire of candidate antigens beyond primary surface proteins.     

Protective immune responses in mice induced by intramuscular and intranasal immunization with a Mycoplasma pneumoniae P1C DNA vaccine

Mycoplasma pneumoniae is an important causative agent of atypical pneumonia. This study was to determine the ability of a DNA expression vector, which encodes the carboxy terminal region of the M. pneumoniae P1 protein (P1C), to induce humoral and cellular immune responses and to protect against M. pneumoniae infection in BALB/c mice. Mice were immunized with pcDNA3.1/P1C by either intramuscular injection (i.m.) or intranasal inoculation (i.n.). Our results showed that p1c DNA immunization generates detectable antibodies specific to M. pneumoniae, and elicits high levels of IgG1, IgG2a, and IgG2b isotypes (P?< 0.01). The levels of IFN-γ and IL-4 in spleen cells of the immunized mice were significantly elevated by immunization via both the i.m. and i.n. methods. Moreover, p1c DNA-immunized mice exhibited detectable protection against M. pneumoniae infection. The lung tissue inflammation was relieved and the histopathologic score (HPS) of pcDNA3.1/P1C-immunized mice was significantly decreased than those in phosphate-buffed saline (PBS) or vaccine-vector-immunized mice (P?< 0.01), whereas there were no significant differences in HPS between i.m. and i.n. vaccination (P?> 0.05). Our results suggest that pcDNA3.1/P1C could be useful for developing a vaccine against M. pneumoniae infection.     

Prophylactic immunization against experimental leishmaniasis. V. Mechanism of the anti-protective blocking effect induced by subcutaneous immunization against Leishmania major infection

The responsiveness of BALB/c mice to protective i.v. immunization with 150,000-rad irradiated or heat-killed Leishmania major promastigotes can be totally suppressed by prior subcutaneous (s.c.) injection of the same "vaccine." Induction of this effect is leishmania specific for although prevention of protection against L. major infection can be obtained with either homologous or Leishmania donovani promastigotes, it does not follow s.c. administration of an immunogenic Trypanosoma cruzi epimastigote preparation. Multiple s.c. injections of irradiated L. major promastigotes do not inhibit the subsequent antibody response of any major isotype to i.v. immunization, but rather induce some priming. The same s.c. injections induced delayed-type hypersensitivity (DTH) reactivity that could be transferred locally or systemically, although it was weaker than in mice with cured infections. Parallel cell-mediated immunity (CMI) responses were also reflected in vitro in specific lymphocyte transformation assays. Despite this evidence of a DTH/helper type of T cell response, transfer of 5 X 10(7) viable T cell-enriched spleen cells from 4 X s.c. immunized donors to normal recipients completely abrogated the protective response to i.v. immunization. Conversely, T cell-depleted (anti-Thy-1.2 + C treated) cells were without effect. The inhibitory T cells were defined by monoclonal antibody pretreatment as possessing an Lyt-1+2-,L3T4+ phenotype. T cells from s.c. immunized donors were also shown, by mixed transfer experiments, to counteract completely the protective effect of T cells from i.v. immunized donors in 550-rad irradiated recipients. They were as potent as suppressor T cells from donors with progressive disease both in this capacity and in abrogating the prophylactic effect of sublethal irradiation itself. The similarities and differences between suppressor and immune effector T cells induced by s.c. or i.v. immunization and those arising in response to leishmanial infection itself are discussed.     

Vault nanocapsules as adjuvants favor cell-mediated over antibody-mediated immune responses following immunization of mice

Background

Modifications of adjuvants that induce cell-mediated over antibody-mediated immunity is desired for development of vaccines. Nanocapsules have been found to be viable adjuvants and are amenable to engineering for desired immune responses. We previously showed that natural nanocapsules called vaults can be genetically engineered to elicit Th1 immunity and protection from a mucosal bacterial infection. The purpose of our study was to characterize immunity produced in response to OVA within vault nanoparticles and compare it to another nanocarrier.

Methodology and Principal Findings

We characterized immunity resulting from immunization with the model antigen, ovalbumin (OVA) encased in vault nanocapsules and liposomes. We measured OVA responsive CD8⁺ and CD4⁺ memory T cell responses, cytokine production and antibody titers in vitro and in vivo. We found that immunization with OVA contain in vaults induced a greater number of anti-OVA CD8⁺ memory T cells and production of IFNγ plus CD4⁺ memory T cells. Also, modification of the vault body could change the immune response compared to OVA encased in liposomes.

Conclusions/Significance

These experiments show that vault nanocapsules induced strong anti-OVA CD8⁺ and CD4⁺ T cell memory responses and modest antibody production, which markedly differed from the immune response induced by liposomes. We also found that the vault nanocapsule could be modified to change antibody isotypes in vivo. Thus it is possible to create a vault nanocapsule vaccine that can result in the unique combination of immunogen-responsive CD8⁺ and CD4⁺ T cell immunity coupled with an IgG1 response for future development of vault nanocapsule-based vaccines against antigens for human pathogens and cancer.     

Comparison of BCG,MPL and cationic liposome adjuvant systems in leishmanial antigen vaccine formulations against murine visceral leishmaniasis

Background  

The development of an effective vaccine against visceral leishmaniasis (VL) caused by Leishmania donovani is an essential aim for controlling the disease. Use of the right adjuvant is of fundamental importance in vaccine formulations for generation of effective cell-mediated immune response. Earlier we reported the protective efficacy of cationic liposome-associated L. donovani promastigote antigens (LAg) against experimental VL. The aim of the present study was to compare the effectiveness of two very promising adjuvants, Bacille Calmette-Guerin (BCG) and Monophosphoryl lipid A (MPL) plus trehalose dicorynomycolate (TDM) with cationic liposomes, in combination with LAg, to confer protection against murine VL.     

Mouse immune response to meningococcal antigens

The mouse immune response against Neisseria meningitidis was studied by using an extract from group Y (Slaterus) known to contain protein antigens common to other meningococci. By using a solid-phase radioimmunoassay, high titers of specific IgM and IgG class antibodies were measured which lasted over 2 months after immunization. These antibodies cross-reacted with similar extracts from other meningococci groups. Bactericidal antibodies directed against protein antigens were also elicited after immunization and they belonged to IgM, IgG2a, and IgG2b isotypes. Cellular immunity, expressed as delayed type hypersensitivity under the conditions tested, could be detected neither in homologous nor heterologous reactions.     

Specific cross-protective antigonococcal immunity in the murine genital tract

Specific acquired immunity to gonococci was studied in systemically immunized mice, challenged with 10(7) gonococci by intrauterine inoculation. Protection after intraperitoneal immunization was monitored by vaginal cultures taken 24 h post-challenge, since events during the first 24 h postexposure to gonococci are crucial in determining the outcome of infection. Mice were protected against gonococcal challenge by two inoculations with either live or boiled gonococci given 4 weeks apart, whereas immunization with one inoculation did not protect against challenge 1 week later. Protection was correlated with high titers of IgG antibody in serum after two immunizations, but not with the high titers of serum IgM antibody found after the one immunization. IgG antibodies, but not IgM antibodies, were shown to pass into genital secretions. Protection could be passively transferred by serum with high titers of antibody. Of most practical importance was the finding that not only were heat-stable antigens protective, but also heterologous protection resulted after immunization with three strains differing in source (disseminated gonococcal infection versus gonorrhea), opacity-transparency characteristics, and serum sensitivity. The data indicate that IgG antibodies resulting from systemic immunization with heat-stable antigens may be able to provide cross-protection immunity against gonorrhea.     

Increase in the immunogenicity of HIV peptide antigens by chemical linkage to polytuftsin (TKPR40).

The use of synthetic peptide antigens in human prophylaxis still suffers from the very important problem of finding suitable carriers devoid of side effects. A desirable carrier for use in humans would be poorly immunogenic by itself, yet it would enhance the immune response to the peptide antigen. In the study reported herein, we examined the role of polytuftsin (TKPR40), a synthetic polymer of the natural immunomodulator tuftsin, as a carrier for synthetic peptides of HIV derived from the gp41 and gp120 proteins. Chimeric immunogens were constructed by chemical linkage between synthetic peptides of HIV and polytuftsin. These were employed for immunization of mice of different MHC haplotypes, and the humoral and cellular immune responses developed against the peptides were assessed by measuring total IgG, IgG, subclasses, T-cell proliferation, and in vitro cytokine release. A significantly stronger immune response was observed in mice immunized with the peptide-polytuftsin conjugates than in mice receiving the peptide dimers (peptide-peptide). Peptide-polytuftsin conjugates induced IgG2a and IgG2b isotype switching after both primary and secondary immunization. In addition, there was a positive correlation between the amounts of cytokines and the shift in the IgG isotypes. These data suggest that the use of polytuftsin as a carrier may increase the immune response against poorly immunogenic synthetic peptides.