Rectal immunization with antigen-containing microspheres induces stronger Th2 responses than oral immunization: a new method for vaccination

Immunogenicity of Recombinant Helicobacter pylori Urease B Administered by Various Routes and with Different Adjuvants

Because of the high prevalence of Helicobacter pylori infection and the morbidity and mortality associated to the disease, development of a preventive vaccine has become a priority. To this goal, we produced recombinant H. pylori urease B (rUreB) and tested its immunogenicity in BALB/c mice when administered as 3 doses (week 0, 4 and 6) by either parenteral (intramuscular) or mucosal routes (intragastric, intranasal, intrarectal) and with the use of various adjuvants (none, CpG, alum or Freund's). The intramuscular route was more immunogenic than any mucosal route; of the mucosas, only intranasal induced modest levels of serum IgG. All adjuvants improved the seroresponse to plain rUreB and, of them, Freund's and alum were equally good and better than CpG ODN 1826. Stool IgA was barely detected by any immunization strategy.

Colonic antigen administration induces significantly higher humoral levels of colonic and vaginal IgA, and serum IgG compared to oral administration

It was hypothesised that different immune responses would be obtained following oral and colonic antigen administration, due to the significant differences in the immune environments of the colon and that of the small intestine. Antigen administration to the mouse colon (via the rectum) was found to generate different profiles of immune responses compared to oral administration (by gavage). Serum IgG and IgA levels in faecal and colonic extracts and in the vaginal wash were significantly higher following colonic administration of soluble (plus cholera toxin B subunit adjuvant) or encapsulated (in microspheres) antigen while smaller differences were seen in the small intestinal IgA levels. This reflects the compartmentalisation within the common mucosal immune system and suggests that the colon may be an appropriate vaccination target for diseases of the colon, and for sexually and vertically transmitted diseases. Antigen was also administered rectally and intramuscularly as controls. Colonic administration was superior to rectal administration, possibly due to the greater amounts of lymphoid tissue in the colon, although the immune response profiles were similar.

The oral immunogenicity of BioProtein, a bacterial single-cell protein, is affected by its particulate nature

The bacterial single-cell protein BioProtein (BP; Norferm Danmark, Odense, Denmark), produced by fermentation of natural gas with methanotrophic bacteria, is a potential protein source for man and animals. For human consumption, removal of the nucleic acid is necessary. Preliminary studies have shown that ingested BP induces a specific immune response. The objective of the present study was to characterize the type of response, its development over time and product-related causative factors. Mice were fed with diets containing 60 g nucleic acid-reduced BP/kg, 240 g nucleic acid-reduced BP/kg, 240 g untreated BP (basic BP)/kg or 240 g casein/kg (control). In another study, mice were fed 240 g basic BP/kg, whole cell-free BP-culture homogenate or control diet. The immune response was monitored using an ELISA for BP-specific immunoglobulin in blood and BP-specific immunoglobulin A in blood and saliva. Ingested BP induced a steady specific mucosal and systemic immune response, characterized by a dose-dependent production of immunoglobulin and immunoglobulin A in blood and immunoglobulin A in saliva. Basic BP and nucleic acid-reduced BP induced identical responses. However, feeding mice BP-culture homogenate induced immunoglobulin A in saliva but there was no systemic response. The antibodies from BP-fed mice cross-reacted with BP-culture homogenate revealing the presence of the same antigenic components in the two products despite the different oral immunogenicity. Thus, ingestion of BP induces a persistent mucosal and systemic immune response of which the systemic response can be avoided by ingesting a BP preparation free of whole cells. This indicates the importance of the non-particulate constitution of single-cell protein products intended for human or animal consumption.

Rectal immunization of mice with hepatitis A vaccine induces stronger systemic and local immune responses than parenteral immunization

Systemic (spleen cell (SPLC), serum antibodies) and intestinal mucosal (Peyer's patch cells (PPC), lamina propria lymphocytes (LPLs), coproantibodies) immune responses were compared in mice immunized with varying doses (144, 72, 36, 18 ELISA units [EU]) of HAVRIX, an alum-adsorbed killed hepatitis A virus (HAV) vaccine, delivered either intrarectally (i.r.) or intraperitoneally (i.p.) in three doses at weekly intervals. HAV-specific IgG, IgM, and IgA antibody responses were evaluated by ELISPOT and EIA and HAV-responsive lymphocytes by lymphocyte stimulation assays. Systemic IgG responses were greater in mice immunized intraperitoneally with 144, 72, and 36EU of HAVRIX, while IgM and IgA responses were greater in PPC and LPL cell populations, serum and coproantibodies of rectally immunized mice, particularly at HAVRIX doses of 36 and 18EU. Rectal immunization at lower doses (36, 18EU) also elicited strong cellular responses in all cell populations while parenteral (i.p.) vaccination, did not. Results suggest that rectal immunization may be a highly effective way of inducing both local and systemic immunity to HAV.