Effective mucosal immunity. Current concepts for vaccine delivery and immune response analysis

Levels of parotid and submandibular/sublingual salivary immunoglobulin A in response to experimental gingivitis in humans

Salivary secretory IgA (s-IgA) is considered to act as an important first line of defense mechanism in the oral cavity. It has therefore been suggested that an increased antigenic load would induce an increase in salivary IgA production. This study investigated the pure glandular levels of salivary IgA in parotid and submandibular/sublingual (SM/SL) saliva during plaque accumulation leading to experimental gingivitis. Starting from regular oral hygiene, 14 healthy, nonsmoking men refrained from all oral hygiene measures for 12 days. On days -2, 0, 3, 6, and 12 a plaque index, a bleeding index, and unstimulated and stimulated saliva from the parotid and the SM/SL glands were measured. Salivary IgA was quantified using a sandwich ELISA. All subjects developed gingivitis as measured by a bleeding index. Compared to baseline the salivary flow rate was increased on day 12. Regarding the secretion rate of IgA there was a statistically significant increase in stimulated parotid saliva but not SM/SL saliva compared to baseline after 6 and 12 days without oral hygiene. No significant changes were observed for the concentration of IgA during the trial. Thus, in healthy subjects with regular oral hygiene the development of plaque induced gingivitis is associated with increased salivary gland output and increased total IgA output levels in stimulated parotid saliva but not in SM/SL saliva.

Monoclonal antibody-mediated modulation of the humoral immune response against mucosally applied Streptococcus mutans

Systemic immunization with antigen coupled to monoclonal antibody (MAb) has been used by several investigators to increase the number of MAb-producing hybridomas against an antigen and to elicit antibodies specific for poorly immunogenic epitopes. This strategy has implications for vaccine design in that protective immunity is not necessarily directed at immunodominant epitopes of pathogens and may be improved by deliberately shifting the immune response toward subdominant epitopes. To our knowledge, no studies to date have addressed the potential for immunomodulatory activity mediated by MAbs bound to mucosally applied antigen. To test whether administration of an exogenous MAb directed against a streptococcal surface protein could influence the humoral immune response, BALB/c mice were immunized orally by gastric intubation or intranasally with Streptococcus mutans alone or S. mutans complexed with a MAb directed against the major surface protein P1. Significant changes in the subclass distribution, as well as the specificity, of anti-P1 serum immunoglobulin G antibodies were demonstrated in groups of mice which received S. mutans coated with the anti-P1 MAb versus those which received S. mutans alone. Alterations in the humoral immune response were dependent on the amount of anti-P1 MAb used to coat the bacteria. In addition, differences in the anti-P1 immune responses were observed between groups of mice immunized via oral versus intranasal routes. In summary, an exogenous MAb complexed with a streptococcal antigen prior to mucosal immunization can influence the immunoglobulin isotype and specificity of the host humoral immune response against the antigen.

Oral immunization of mice with a glycoconjugate vaccine containing the O157 antigen of Escherichia coli O157:H7 admixed with cholera toxin fails to elicit protection against subsequent colonization by the pathogen

It has been postulated that a humoral immune response directed against the O157 antigen of Escherichia coli O157:H7, and expressed in the intestine, might afford protection from colonization and consequent infection by this enteric pathogen. The present study was conducted to determine whether such an immune response can be experimentally generated in mice. To this end, mice were orally immunized with a glycoconjugate vaccine consisting of horse serum albumin and the O157 polysaccharide admixed with the mucosal adjuvant, cholera toxin. Mice consistently developed robust local and systemic immune responses to the cholera toxin adjuvant, but were far from uniformly reactive to the test vaccine. Moreover, vaccinated mice were as susceptible to transient intestinal colonization following challenge with an isolate of E. coli O157:H7 as unvaccinated control mice. These results indicate that this vaccination approach is unlikely to be straightforward in target bovine or human hosts.Key words: Escherichia coli O157:H7, glycoconjugate vaccine, mucosal immunity, mice.

Salmonella landau as a live vaccine against Escherichia coli O157:H7 investigated in a mouse model of intestinal colonization

The present study was performed to assess the potential of a humoral mucosal immune response directed against the O157 antigen of Escherichia coli O157:H7 to prevent intestinal colonization by the pathogen. To this end, mice were gavaged with inocula of Salmonella landau, a Salmonella strain that naturally expresses the O157 antigen. Salmonella landau was avirulent for mice. Despite this, mice exposed to S. landau developed high titres of serum and coproantibodies against the O157 antigen. These mice, compared with controls, demonstrated some ability to resist transient intestinal colonization by an oral inoculum of an isolate of E. coli O157:H7. These findings suggest that a local immune response directed against the O157 antigen might increase host resistance to this pathogen.Key words: Salmonella landau, Escherichia coli O157:H7, mucosal immunity, mice.

Parenteral immunization with a glycoconjugate vaccine containing the O157 antigen ofEscherichia coliO157:H7 elicits a systemic humoral immune response in mice, but fails to prevent colonization by the pathogen

The results of the present study show that whereas both BALB/c and C57BL/6 mice parenterally inoculated with a horse serum albumin - Escherichia coli O157 antigen conjugate vaccine develop systemic, specific antibodies to the carrier protein, only the former mice routinely develop antibodies to the carbohydrate O157 moiety. However, little convincing evidence was found to show that these antibodies transuded into the intestinal tract either naturally or in response to an oral inoculum of the pathogen. Moreover, this vaccination procedure failed to protect mice against intestinal colonization following oral challenge with the pathogen. Thus, the results of this study suggest that parenteral vaccination might be an unsuitable strategy for combatting E. coli O157:H7 organisms located in the gut.Key words: Escherichia coli, glycoconjugate vaccine, mice.

Female reproductive tract immunity in bovine trichomoniasis

PROBLEM

Mechanisms of protective immunity in the female reproductive tract are poorly understood. For sexually transmitted diseases, bovine trichomoniasis is a useful model because it resembles human trichomoniasis to some extent, and antibodies play an important role in protection against these extracellular parasites. Protective efficacy was compared in animals with genital responses of predominantly immunoglobulin G (IgG) or predominantly IgA antibodies to a purified surface antigen of Tritrichomonas foetus.

METHOD OF STUDY

Immunization of mice by various routes with immunoaffinity-purified T. foetus surface antigen (TF1.17) or killed cells was used to define the best routes and antigen combinations to give predominantly IgG or IgA antibodies to TF1.17 antigens in genital secretions. Cattle were then immunized either subcutaneously (SC) two times with TF1.17 antigen and once SC with killed T. foetus or twice SC with TF1.17 antigen and once intravaginally with killed T. foetus. All immunizations were in Quil A adjuvant. Controls were not immunized. Animals were challenged intravaginally with 10(6) T. foetus 3 weeks after the third immunization. Vaginal mucus was collected weekly for culture and antibody assays. Serum was collected weekly, and uterine secretions were collected at 10 weeks post-challenge. Tissues were fixed at 10 weeks also.

RESULTS

Murine studies showed systemic priming with vaginal boosting gave the highest genital IgA responses. In cattle, systemic immunization (group S) induced high IgG1 antibody levels in vaginal secretions. Systemic priming with vaginal boosting (group S/V) primed for an anamnestic vaginal IgA response after challenge with T. foetus. Cattle with predominantly IgG or predominantly IgA responses in vaginal secretions either did not become infected or cleared infection faster than controls. Uterine IgA responses at 10 weeks were highest in the vaginally boosted group, but other responses were not different from the controls at this time point. Microscopic examination of genital tissues showed subepithelial infiltration of mononuclear cells in all groups. Lymphoid aggregates or nodules were detected in vaginal sections in cattle of groups S/V and C as well as in uterine sections of all animals in all three groups.

CONCLUSIONS

Both IgG and IgA antibodies to T. foetus superficial antigen were associated with protection. The timing of the response was related to the time of clearance. Lymphoid organization in the vagina and uterine tissues suggested development of mucosal inductive sites.

Induction of mucosal and systemic responses against human immunodeficiency virus type 1 glycoprotein 120 in mice after oral immunization with a single dose of a Salmonella-HIV vector

Previous studies from our group showed that a Salmonella-HIV vector vaccine that expressed recombinant HIV-1 envelope protein gp120 stably in the vector cytoplasm elicited type 1 helper T cell (Th1) responses to gp120. Despite the promise of such vaccines, a major limitation in their use was that multiple immunizations were required to elicit even small responses. For this reason, we sought a modified vector configuration that would induce more potent gp120-specific T cell responses exhibiting a broader spectrum of effector functions after a single inoculation. In this article we describe the construction and immunogenicity of a Salmonella-HIV vector that displays a truncated derivative of HIV-1(IIIB) envelope in the periplasm of the vector. A single oral dose of this Salmonella vector, called H683(pW58-asd+), generated a gp120-specific proliferation response in the spleen 14 days after immunization. In agreement with our previous findings, the gp120-specific splenic CD4+ T cells elicited by H683(pW58-asd+) displayed a Th1 phenotype; however, gp120-specific splenic CD4+ Th2 cells were also evident. In addition, this strain induced strong gp120-specific IgA antibody-secreting cell (ASC) responses in the intestinal lamina propria and mesenteric lymph nodes. As many as 2% of the total lamina propria and mesenteric lymph node IgA ASCs were found to be specific for gp120 28 days after a single oral dose of H683(pW57-asd+). Because the proliferative response following a single dose of H683(pW58-asd+) was comparable to that seen previously after three doses of an analogous construct expressing recombinant gp120 in the cytoplasm, these observations suggest that Salmonella-vectored secreted HIV-1 antigens elicit higher T cell responses than their cytoplasmically bound analogs.

New strategies for using mucosal vaccination to achieve more effective immunization

Future progress in vaccination will be significantly advanced by application of emerging technologies for immunization of mucosal surfaces. It should now be possible to maximize the antigenicity of many vaccines and facilitate their interaction with appropriate lymphoid tissues to induce protective cellular and humoral responses. Mucosal vaccines requiring no more than two doses are achievable with current technologies. Living vaccines have been among the most promising candidates for mucosal vaccination, but with few exceptions their promise is still to be realized. Development of new microencapsulated delivery systems and adjuvants has made non-living vaccines reasonable options for mucosal immunization. To be practical, such vaccines should be developed as combined agent vaccines, possibly deliverable by multiple mucosal routes. Although strategies to be used for specific mucosal vaccines will depend upon a number of factors pertinent to the disease agent, in concept an adjuvant administered with inactivated but maximally antigenic pathogens or their recombinant adhesive subcomponents could prove to be among the more practical mucosal vaccine options for use globally.