gms | German Medical Science

Lipopolysaccharide-binding protein (LBP) is an integral part of the innate immune system's response to Gram-negative bacteria. Among other effects, the concentration of neutrophil derived BPI (bactericidal permeability increasing protein) needed to kill bacteria is reduces by 10,000-fold for it acts as an opsonin. We hypothesized that LBP-knockout (LBPko) mice will have compromised host defense against Gram-negative bacteria using a burn model and higher wound infection rates compared to wild-types.

Female wild-type C57BL6 mice and corresponding LBPkos received a 20% partial thickness burn wound. Using pooled GeneChip probe array we screened for genes differentially expressed in the skin of the 2 strains of mice 6 hours postburn. Resulting we focused on skin mRNA levels of the chemokine GRO-1 (MIP2) and interleukins IL-1, IL-6, IL-10 and TNF. Following, 105 Pseudomonas aeruginosa were applied topically in a similar setting and quantitative Pseudomonas counts per g skin performed 24 hours later. Real time RT-PCR was used to compare mRNA levels of these cytokines within Pseudomonas-infected burn wounds from LBPko versus C57BL6 mice.

In the GeneChip analysis (6 hrs postburn) GRO-1 was upregulated more than 50 times. Pseudomonas bacterial counts were 13 times lower in LBPko animals (p<.05) at 24 hours. In the real time RT-PCR analysis, IL-6 gene expression was significantly higher in LBPko (p<.04, [Fig. 1]) as was TNF and IL-10.

Contrary to our initial hypothesis, the bacterial numbers in LBPko animals were lower than in wild-types using the burn model. Absent LBP leads to higher gene expression of the neutrophil-attractant GRO-1 (MIP2) chemokine as well as the proinflammatory cytokines in our experimental design. Further investigation is needed to shed light on the bactericidal host defense mechanisms which appear to be compensating for absent LBP in LBPko animals.