Vector Transmission of Leishmania Abrogates Vaccine-Induced Protective Immunity

Numerous experimental vaccines have been developed to protect against the cutaneous and visceral forms of leishmaniasis caused by infection with the obligate intracellular protozoan Leishmania, but a human vaccine still does not exist. Remarkably, the efficacy of anti-Leishmania vaccines has never been fully evaluated under experimental conditions following natural vector transmission by infected sand fly bite. The only immunization strategy known to protect humans against natural exposure is “leishmanization,” in which viable L. major parasites are intentionally inoculated into a selected site in the skin. We employed mice with healed L. major infections to mimic leishmanization, and found tissue-seeking, cytokine-producing CD4+ T cells specific for Leishmania at the site of challenge by infected sand fly bite within 24 hours, and these mice were highly resistant to sand fly transmitted infection. In contrast, mice vaccinated with a killed vaccine comprised of autoclaved L. major antigen (ALM)+CpG oligodeoxynucleotides that protected against needle inoculation of parasites, showed delayed expression of protective immunity and failed to protect against infected sand fly challenge. Two-photon intra-vital microscopy and flow cytometric analysis revealed that sand fly, but not needle challenge, resulted in the maintenance of a localized neutrophilic response at the inoculation site, and removal of neutrophils following vector transmission led to increased parasite-specific immune responses and promoted the efficacy of the killed vaccine. These observations identify the critical immunological factors influencing vaccine efficacy following natural transmission of Leishmania

Campylobacter jejuni induces diverse kinetics and profiles of cytokine genes in INT-407 cells

OBJECTIVE: To examine the kinetic ability of embryonic human epithelial INT-407 cells to express messenger ribonucleic acid mRNA for various cytokines and chemokines in response to Campylobacter jejuni C. jejuni stimulation. METHODS: In an experimental single-blind study, cultured embryonic human epithelial INT-407 cells were treated with different concentrations of viable C. jejuni, its sonicated, and filtered supernatant. A modified non-radioactive in situ hybridization using probe cocktails was used to measure mRNA levels for the pro-inflammatory cytokines interleukin IL-1beta, IL-6, interferon-gamma IFN-gamma, tumour necrosis factor TNF-alpha, transforming growth factor TGF-beta1, and IL-8, and the anti-inflammatory cytokines, IL-4 and IL-10. The study was carried out from September 2005 to March 2007 at the Department of Microbiology, Immunology, and Infectious Diseases, College of Medicine, Arabian Gulf University, Bahrain. RESULTS: Viable C. jejuni, sonicated bacteria and fil..

Evaluation of s.c. route of immunization by homologous radio attenuated live vaccine in experimental murine model of visceral leishmaniasis

Our previous studies in BALB/c mice showed substantial protection against the experimental murine visceral leishmaniasis (MVL) when the animals were immunized with γ-irradiated live Leishmania donovani parasites through intra peritoneal (i.p.) and intra muscular (i.m.) routes respectively. The observations encouraged us to check the prophylactic efficacy of subcutaneous (s.c.) route as it is better alternative for human trial. The mice immunized with two subsequent doses of the radio attenuated homologous vaccine were challenged with virulent L. donovani parasites. Seventy-five days post infection, the animals were sacrificed. The extent of protection against the disease was evaluated by assessing the reduction of parasite burden in spleen and liver, the generation of free radicals (NO & ROS) and release of the cytokines from T-lymphocyte helper 1 (Th 1) and T-lymphocyte helper 2 (Th 2) along with the measurement of the serum immunoglobulins. The reductions in parasitic burden were observed up to 21 and 24 % in spleen and liver of the immunized groups with NO and ROS productions 27 and 34 % respectively. Whereas the increase in IFN gamma releases was between 19 and 34 %, the decrease in IL-10 release was not more than 22 %. This indicates the failure of the establishment of pronounced Th1 ambience which was further corroborated by the observed IgG2a and IgG1 ratio. The present study when compared with our previous observations with i.m. and i.p. routes revealed that s.c. route may not be a good choice for the use of radio attenuated vaccine