Publications

Melioidosis is a severe infectious disease caused by the saprophytic facultative intracellular pathogen Burkholderia pseudomallei. The disease is endemic in Southeast Asia and Northern Australia, and no effective vaccine exists. To describe human cell-mediated immune responses to B. pseudomallei and to identify candidate antigens for vaccine development, the ability of antigen-pulsed monocyte-derived dendritic cells (moDCs) to trigger autologous T-cell responses to B. pseudomallei and its products was tested. moDCs were prepared from healthy individuals exposed or not exposed to B. pseudomallei, based on serological evidence. These were pulsed with heat-killed B. pseudomallei or purified antigens, including ABC transporters (LolC, OppA, and PotF), Bsa type III secreted proteins (BipD and BopE), tandem repeat sequence-containing proteins (Rp1 and Rp2), flagellin, and heat shock proteins (Hsp60 and Hsp70), prior to being mixed with autologous T-cell populations. After pulsing of cells with either heat-killed B. pseudomallei, LolC, or Rp2, coculturing the antigen-pulsed moDCs with T cells elicited gamma interferon production from CD4+ T cells from seropositive donors at levels greater than those for seronegative donors. These antigens also induced granzyme B (cytotoxic) responses from CD8+ T cells. Activation of antigen-specific CD4+ T cells required direct contact with moDCs and was therefore not dependent on soluble mediators. Rp peptide epitopes recognized by T cells in healthy individuals were identified. Our study provides valuable novel data on the induction of human cell-mediated immune responses to B. pseudomallei and its protein antigens that may be exploited in the rational development of vaccines to combat melioidosis.

Bluetongue virus (BTV) is an economically important arbovirus of ruminants transmitted by Culicoides biting midges. Vector control using residual spraying or application to livestock is recommended by many authorities to reduce BTV transmission; however, the impact of these measures in terms of both inflicting mortality on Culicoides and subsequently upon BTV transmission is unclear. This study consisted of a standardized World Health Organization laboratory assay to determine the susceptibility of European Culicoides species to deltamethrin and a field trial based upon allowing individuals of a laboratory strain of Culicoides nubeculosus Meigen to feed upon sheep treated with Butox 7.5 pour-on (a deltamethrin-based topical formulation). Susceptibility in the laboratory trial was higher in colony C. nubeculosus (24-hLC(90) = 0.00106%), than in field populations of Culicoides obsoletus Meigen (24-h LC(90) = 0.00203%) or Culicoides imicola Kieffer (24-h LC(90) = 0.00773%). In the field, the pour-on formulation was tested with a total of 816 C. nubeculosus specimens fed upon on the thigh of treated sheep. The study revealed a maximum mortality rate of 49% at 4 d postapplication, and duration of lethal effect was predicted to be as short as 10 d, despite testing being carried out with a highly susceptible strain. The reasons for this low efficacy are discussed with reference both to the potential for lack of spread of the active ingredient on the host and feeding patterns of the major potential vector species on the sheep host. Practical implications for vector control strategies during BTV incursions are also detailed.

In most mammals, the MHC class I molecules are polymorphic and determine the specificity of peptide presentation, whereas the transporter associated with antigen presentation (TAP) heterodimers are functionally monomorphic. In chickens, there are two classical class I genes but only one is expressed at a high level, which can result in strong MHC associations with resistance to particular infectious pathogens. However, the basis for having a single dominantly expressed class I molecule has been unclear. Here we report TAP1 and TAP2 sequences from 16 chicken lines, and show that both genes have high allelic polymorphism and moderate sequence diversity, with variation in positions expected for peptide binding. We analyze peptide translocation in two MHC haplotypes, showing that chicken TAPs specify translocation at three peptide positions, matching the peptide motif of the single dominantly expressed class I molecule. These results show that coevolution between class I and TAP genes can explain the presence of a single dominantly expressed class I molecule in common chicken MHC haplotypes. Moreover, such coevolution in the primordial MHC may have been responsible for the appearance of the antigen presentation pathways at the birth of the adaptive immune system.