Interleukin-11 Drives Early Lung Inflammation during Mycobacterium tuberculosis Infection in Genetically Susceptible Mice

IL-11 is multifunctional cytokine whose physiological role in the lungs during pulmonary tuberculosis (TB) is poorly understood. Here, using in vivo administration of specific antibodies against IL-11, we demonstrate for the first time that blocking IL-11 diminishes histopathology and neutrophilic infiltration of the lung tissue in TB-infected genetically susceptible mice. Antibody treatment decreased the pulmonary levels of IL-11 and other key inflammatory cytokines not belonging to the Th1 axis, and down-regulated IL-11 mRNA expression. This suggests the existence of a positive feedback loop at the transcriptional level, which is further supported by up-regulation of IL-11 mRNA expression in the presence of rIL-11 in in vitro cultures of lung cells. These findings imply a pathogenic role for IL-11 during the early phase of Mycobacterium tuberculosis-triggered disease in a genetically susceptible host

Treatment with anti-IL-11 antibodies significantly attenuates the severity of TB in I/St mice.

<p>(A) ∼3-fold decrease in lung CFU counts compared to control animals. (B and C) Lung pathology in individual animals. None of anti-IL-11-treated mice developed necrotic TB foci evident in control mice <i>a</i>, <i>d</i> and <i>g</i> (circled). (D) Statistical evaluation of the proportion of inflamed lung tissue. CFU counts and morphometry were performed in all mice included in 2 independent experiments (total N = 16 and 17 for experimental and control groups, respectively). Histology is displayed for individual mice analyzed in one experiment (N = 7 for each group).</p

Protein levels of IL-11 affect IL-11 mRNA expression.

<p>(A) <i>In vivo</i> administration of anti-IL-11 antibodies leads to a selective down-regulation of IL-11 mRNA. The level of expression was quantified in 5 individual mice per group, using qrt-PCR and normalization against the level of GAPDH expression. Results obtained in 1 of 2 similar experiments are expressed as mean ± SEM (for IL-11 expression <i>P</i> = 0.021, for other cytokines <i>P</i>>0.05). (B) Introduction of 100 ng/ml rIL-11 in cultures of lung cells up-regulates the expression of IL-11 mRNA. Results of two similar experiments are expressed as mean of 3 wells ± SEM (<i>P</i><0.01, ANOVA, compared to negative controls and cultures stimulated with 10 ng/ml IL-11).</p

Properties of anti-IL-11 polyclonal antibodies.

<p>(A) Reactivity of affinity purified rabbit globulin preparation against mIL-11 assessed in ELISA format. No reactivity was found in pre-immune globulin (diamonds); immunoglobulin from rabbits immunized thrice with rmIL-11 showed very strong reactivity (squares); after exhaustion on mycobacterial sonicate adsorbent, specific anti-IL-11 reactivity dropped but was readily detected (triangles). (B) Immune blotting with rmIL-11 with polyclonal rabbit anti-mIL-11 antibodies (preparation identical to one displayed as triangles in (A). Tracks: 1, 2 – immune rabbits 1 and 2; 3, 4 – pre-immune rabbits 1 and 2; 5 – conjugate-free control.</p

Two weeks after TB challenge the level of IL-11 mRNA increases ∼1 log in the lungs of TB-susceptible I/St but does not change in TB-resistant A/Sn mice.

<p>Mean ± SEM expression level plotted against that of GABDT in 4 individual mice per group is displayed (<i>P</i><0.01, ANOVA, between naïve and infected I/St mice).</p

Anti-IL-11 antibody therapy decreases levels of IL-11 and pro-inflammatory factors in the lung tissue without shifting the IL-12 – IFN-γ/IL-10 balance.

<p>Cytokine contents in lung homogenates were assessed by ELISA for 4 mice in each group. The results of one of two similar experiments are displayed as mean ± SEM.</p