Lipopolysaccharide analogs improve efficacy of acellular pertussis vaccine and reduce type I hypersensitivity in mice

Pertussis is an infectious disease of the respiratory tract that is caused by the gram-negative bacterium Bordetella pertussis. Although acellular pertussis (aP) vaccines are safe, they are not fully effective and thus require improvement. In contrast to whole-cell pertussis (wP) vaccines, aP vaccines do not contain lipopolysaccharide (LPS). Monophosphoryl lipid A (MPL) and Neisseria meningitidis LpxL2 LPS have been shown to display immune-stimulating activity while exerting little endotoxin activity. Therefore, we evaluated whether these LPS analogs could increase the efficacy of the aP vaccine. Mice were vaccinated with diphtheria-tetanus-aP vaccine with aluminum, MPL, or LpxL2 LPS adjuvant before intranasal challenge with B. pertussis. Compared to vaccination with the aluminum adjuvant, vaccination with either LPS analog resulted in lower colonization and a higher pertussis toxin-specific serum immunoglobulin G level, indicating increased efficacy. Vaccination with either LPS analog resulted in reduced lung eosinophilia, reduced eosinophil numbers in the bronchoalveolar lavage fluid, and the ex vivo production of interleukin-4 (IL-4) by bronchial lymph node cells and IL-5 by spleen cells, suggesting reduced type I hypersensitivity. Vaccination with either LPS analog increased serum IL-6 levels, although these levels remained well below the level induced by wP, suggesting that supplementation with LPS analogs may induce some reactogenicity but reactogenicity considerably less than that induced by the wP vaccine. In conclusion, these results indicate that supplementation with LPS analogs forms a promising strategy that can be used to improve aP vaccines.

Host genetics of Bordetella pertussis infection in mice: significance of Toll-like receptor 4 in genetic susceptibility and pathobiology

The susceptibility to and the severity of Bordetella pertussis infections in infants and children varies widely, suggesting that genetic differences between individuals influence the course of infection. We have previously identified three novel loci that influence the severity of whooping cough by using recombinant congenic strains of mice: Bordetella pertussis susceptibility loci 1, 2, and 3 (Bps1, -2, and -3). Because these loci could not account for all genetic differences between mice, we extended our search for additional susceptibility loci. We therefore screened 11 inbred strains of mice for susceptibility to a pertussis infection after intranasal infection. Susceptibility was defined by the number of bacteria in the lungs, being indicative of the effect between the clearance and replication of bacteria. The most resistant (A/J) and the most susceptible (C3H/HeJ) strains were selected for further genetic and phenotypic characterization. The link between bacterial clearance and chromosomal location was investigated with 300 F2 mice, generated by crossing A/J and C3H/HeJ mice. We found a link between the delayed clearance of bacteria from the lung and a large part of chromosome 4 in F2 mice with a maximum log of the odds score of 33.6 at 65.4 Mb, which is the location of Tlr4. C3H/HeJ mice carry a functional mutation in the intracellular domain of Tlr4. This locus accounted for all detectable genetic differences between these strains. Compared to A/J mice, C3H/HeJ mice showed a delayed clearance of bacteria from the lung, a higher relative lung weight, and increased body weight loss. Splenocytes from infected C3H/HeJ mice produced almost no interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha) upon ex vivo restimulation with B. pertussis compared to A/J mice and also showed a delayed gamma interferon (IFN-gamma) production. TNF-alpha expression in the lungs 3 days after infection was increased fivefold compared to uninfected controls in A/J mice and was not affected in C3H/HeJ mice. In conclusion, Tlr4 is a major host factor explaining the differences in the course of infection between these inbred strains of mice. Functional Tlr4 is essential for an efficient IL-1-beta, TNF-alpha, and IFN-gamma response; efficient clearance of bacteria from the lung; and reduced lung pathology.

Induction of Nevi and Skin Tumors in Ink4a/Arf Xpa Knockout Mice by Neonatal, Intermittent, or Chronic UVB Exposures

Nevi and melanomas correlate to childhood and intermittent solar UV exposure, xeroderma pigmentosum patients run increased risk, and p16(Ink4a) expression is often lost in malignant progression. To ascertain the effect of these risk factors, pigmented hairless Ink4a/Arf-, Xpa- knockout mice were subjected to various combinations of neonatal [7,12-dimethylbenz(a)anthracene (DMBA) or UVB exposure] and adult treatments (12-O-tetradecanoylphorbol-13-acetate or subacute daily UVB exposure or intermittent overexposure). Nevi occurred earliest, grew largest, and were most numerous in mice exposed to DMBA followed by intermittent UVB overexposure [effect of six minimal edemal doses (MED), 1 x /2 weeks > 4 MED 1 x /wk]. Neonatal UV exposure enhanced nevus induction but lost its effect after 200 days. The Xpa(-/-) mice proved exquisitely sensitive to UV-driven nevus induction, indicating the involvement of pyrimidine dimer DNA lesions, but Xpa(+/+) mice developed many more nevi (>40 per mouse) at high UV dosages not tolerated by Xpa(-/-) mice. Ink4a/Arf(-/-) mice developed most skin tumors faster, but surprisingly developed nevi slower than their heterozygous counterparts especially after neonatal UV exposure. Despite raising >1,600 nevi, only six melanomas arose in our experiments with Ink4a/Arf knockout mice (five of which in Xpa(+/+) mice at high UV dosages). In contrast to human nevi, these nevi lacked hotspot mutations in Braf or Ras genes, possibly explaining the lack of malignant progression in the Ink4a/Arf(-/-) mice. Hence, although our experiments did not effectively emulate human melanoma, they provided clear evidence that intermittent UV overexposure strongly stimulates and the Ink4a/Arf(-/-) genotype may actually impair nevus development.

Genetic control of Bordetella pertussis infection: identification of susceptibility loci using recombinant congenic strains of mice

Susceptibility to and severity of Bordetella pertussis infection in infants and children vary widely. The spectrum of clinical symptoms ranges from subclinical infection to mild disease, severe whooping cough, and death. The aims of this study were to examine genetic susceptibilities of mice to B. pertussis and to identify genetic loci in the mouse genome that are involved in susceptibility to B. pertussis infection. For this purpose we screened two sets of recombinant congenic strains (RCS) of mice, HcB and CcS, for differences in the numbers of bacteria in the lung 7 days after inoculation. For both CcS and in HcB mice, a wide range in numbers of bacteria in the lung was found, suggesting that the course of infection is under multigenic control. From both RCS sets of mice, we selected one strain to identify possible susceptibility loci in F(2) hybrid mice. The degree of lung colonization 7 days postinoculation in these F(2) mice was evaluated in relation to genetic markers by linkage analysis. We found three novel loci that are involved in the control of B. pertussis infection. One locus, designated B. pertussis susceptibility locus 1 (Bps-1), was identified on chromosome 12. The presence of the C57BL/10 genome on this locus instead of the C3H genome significantly decreased the number of B. pertussis bacteria in the lung. Bps-1 has a dominant-positive effect on the clearance of B. pertussis from the lung. The function of most genes in this region is unknown. Two other loci, Bps-2 and Bps-3, showed genetic interaction and are located on chromosomes 5 and 11. We aim to identify the gene(s) in these regions which modify susceptibility to B. pertussis.