Analogous Cytokine Responses toBurkholderia pseudomalleiStrains Contrasting in Virulence Correlate with Partial Cross-Protection in Immunized Mice

Abstract

Cytokine mRNA levels were assessed in Burkholderia pseudomallei-susceptible BALB/c mice and B. pseudomallei-resistant C57BL/6 mice following administration of a sublethal dose of less virulent (LV) B. pseudomallei, a candidate immunogen tested for protection against a highly virulent (HV) challenge. Compared on the basis of the bacterial loads, the cytokine patterns induced by HV and LV B. pseudomallei were similar, involving gamma interferon, interleukin-10, and other cytokines. Partial cross-protection between B. pseudomallei strains is shown to be associated with cytokine profiles involving both type 1 and type 2 cytokines.Melioidosis is a potentially acute fulminating disease of humans and animals caused by the gram-negative intracellular bacterium Burkholderia pseudomallei (36). Infection occurs by subcutaneous inoculation of contaminated soil or surface water and can result in latent infection or a diverse range of clinical presentations (6). As recently reported by Currie et al. (8), recrudescence of disease may occur years after initial exposure, which suggests that the immune responses induced may not be effective for clearance of the organism. Differences in host and pathogen virulence factors are known to be important in determining disease severity (33). Gamma interferon (IFN-␥) plays a critical role in innate host resistance during primary infection (26), but mechanisms of adaptive immunity have not been widely studied. BALB/c mice are susceptible to infection with highly virulent (HV) B. pseudomallei, whereas C57BL/6 mice are relatively resistant (17). Cytokine responses following an HV B. pseudomallei challenge (34) are unlike those seen in other models of intracellular infection, and resistance and susceptibility do not correlate with divergent cytokine profiles commonly associated with development of distinct T helper cell subsets. Instead, early cytokine profiles are similar in BALB/c and C57BL/6 mice, with the only demonstrated difference being in the magnitude of the cytokine response (34). Responses involving a similar range of cytokines have been reported in patients (4,11,31).Characterization of less virulent (LV) strains of B. pseudomallei (12,13,35) allows us to determine their potential as candidate immunogens for induction of adaptive immunity against HV B. pseudomallei. In models of infection with other intracellular pathogens (3,5,22,27,28,29), cytokine responses are dependent upon the level of virulence of the challenge strain. The present study investigated the influence of B. pseudomallei virulence on disease progression and cytokine responses in melioidosis. Cytokine profiling of the spleen and liver was carried out by reverse transcription-PCR, and bacterial growth in the blood, liver, and spleen was determined. Immunization experiments were performed by using LV B. pseudomallei as a candidate immunogen for protection against an HV challenge to analyze the relationship between cytokine responses and immunity to B. pseudomallei.The B. pseudomallei strains used were NCTC 13178 (H...

A model of immunity to Burkholderia pseudomallei: unique responses following immunization and acute lethal infection

“…However, it is possible that latent infection, not detectable by standard culture techniques, resulting from immunization with CL04 might reappear subsequently considering the extremely chronic recrudescent nature of melioidosis. The current observations are consistent with previously reported clearance rates for less virulent B. pseudomallei [15] and, combined with the comparative immunization data in this study illustrates unique immunogenicity traits amongst B. pseudomallei isolates even where individual strains are equivalent in virulence and in clearance kinetics in mice. Immunogenicity of B. pseudomallei isolates therefore appears to be associated with specific bacterial components present in particular strains.…”

“…Immunization-induced immunity could not protect mice from higher LC doses. Moreover, considerable bacterial loads at several weeks after LC in immunized mice illustrates non-sterilizing immunity, which is consistent with a previous study [15]. Gene microarray assessment of mRNA expression identified several unique immunization-associated genes including GM-CSF, Bad and TERT/TP2 in BALB/c mice and CDK5 in C57BL/6 mice.…”

“…Using a primary-boost-LC approach we have demonstrated that both BALB/c and C57BL/6 mice can be protected against lethal B. pseudomallei infection using CL04. Compared to alternative-immunization strategies tested in the extensive initial screening in this study and by strain comparisons with a previous study [15], we show that protection generated in response to immunization with CL04 is more robust than that generated in response to other strains and is dependent on factors including immunization dose, bacterial viability and booster administration. Analysis of the kinetics of bacterial survival in the optimized immunization model shows that the primary immunization dose is rapidly and efficiently cleared to less than 1% of the initial immunization dose within a few days of administration, which is also true for the subsequent booster.…”

Burkholderia pseudomallei Capsule Exacerbates Respiratory Melioidosis but Does Not Afford Protection against Antimicrobial Signaling or Bacterial Killing in Human Olfactory Ensheathing Cells

“…; however, these were insufficient to inhibit the hyperproduction of proinflammatory responses in the lungs, NALT, and OM. Interestingly, the levels of many cytokines in the lungs, NALT, and OM were not proportionate to the B. pseudomallei colonization load in the tissue; similar results were reported for the spleen (66).…”

Interleukin-12 induces a Th1-like response to Burkholderia mallei and limited protection in BALB/c mice

“…However, in BALB/c mice, the level of expression of some of these cytokines including IFN-␥ was greater than in C57BL/6 mice, which was interpreted as a possible role for endotoxic shock and a cytokine-mediated immunopathology in the development of melioidosis [39]. It was further found that the mixed Th1-and Th2-like cytokine response induced by highly virulent and less virulent strains of B. pseudomallei, correlated with partial cross-protection between the two strains in mice previously immunized with the less virulent B. pseudomallei candidate vaccine strain [40].…”