title: Oral vaccination of mice with lipid-encapsulated Mycobacterium bovis BCG: Effect of reducing or eliminating BCG load on cell-mediated immunity.
abstract: Oral delivery of lipid-encapsulated BCG represents an effective method for vaccination against tuberculosis (Tb). This method establishes live, replicating BCG in the lymphatic tissues of the alimentary tract, and promotes systemic-level cell-mediated immunity (CMI) and consequent protection against virulent mycobacterial challenge. Here, we investigated the effects of reducing or eliminating the BCG load on CMI responses in mice. Mice receiving a standard immunising dose of approximately 10(7) BCG (range, 1-5 x 10(7)) developed mycobacterial antigen-specific lymphocyte transformation (LT) responses, as well as interleukin-2 (IL-2) and gamma-interferon (IFN-gamma) secretion, at 8 and 18 weeks post-oral vaccination. These responses were concurrent with establishment of viable, replicating BCG in the alimentary tract lymphatics in over 90% of cases. Reducing the immunising dose by 10-fold reduced the magnitude of CMI, concurrent with abridged establishment of BCG in the lymphatics; reducing the dose 100-fold ablated BCG establishment, and diminished the production of IFN-gamma by antigen-stimulated lymphocytes of these mice. In mice immunised using the standard dose, replicating BCG were eliminated from the alimentary tract lymphatics using selective antibiotics. Interestingly, while lymphocyte transformation and interleukin-2 responses remained largely unaltered in these mice, levels of IFN-gamma produced by antigen-stimulated lymphocytes were shown to be reduced significantly. This study identifies a dosage threshold for effective oral vaccination using lipid-encapsulated BCG, and furthermore highlights the requirement of on-going intra-lymphatic BCG replication for the maintenance of strong IFN-gamma production, above other indicator CMI responses.
authors.affiliation: Centre for Innovation, University of Otago, P.O. Box 56, Dunedin, New Zealand. frank.cross@stonebow.otago.ac.nz
authors.forename: M L
authors.initials: ML
authors.lastname: Cross
authors.forename: M R
authors.initials: MR
authors.lastname: Lambeth
authors.forename: Y
authors.initials: Y
authors.lastname: Coughlan
authors.forename: F E
authors.initials: FE
authors.lastname: Aldwell
mesh_terms: D000276:Adjuvants, Immunologic / Q000008:administration & dosage / Q000494:pharmacology*; D000284:Administration, Oral; D000818:Animals; D001500:BCG Vaccine / Q000008:administration & dosage / Q000494:pharmacology*; D015169:Colony Count, Microbial; D004305:Dose-Response Relationship, Drug; D004337:Drug Carriers; D005260:Female; D007111:Immunity, Cellular / Q000187:drug effects*; D008081:Liposomes; D051379:Mice; D008807:Mice, Inbred BALB C
chemical_list: D000276:Adjuvants, Immunologic; D001500:BCG Vaccine; D004337:Drug Carriers; D008081:Liposomes