Inhibition of abl tyrosine kinase supports antimicrobial activity in human alveolar macrophages

Objective: Inhibition of abl tyrosine kinase by Gleevec® has revolutionized the therapy of chronic myeloic leukemia. The therapeutic manipulation of this ubiquitously expressed enzyme requires careful evaluation of potential side effects. This study was designed to investigate the functional implication of Gleevec® on the interaction of Mycobacterium tuberculosis (M.Tb) and its natural host cell, the alveolar macrophage.

Methods: Human alveolar macrophages were purified from bronchoalveolar lavage cells and infected with virulent M. Tb. Intracellular growth, phagosomal acidification and the expression of antimicrobial peptides was compared in the presence or absence of Gleevec.

Results: First we established by Western blot analysis that infection with M. Tb induces abl tyrosine kinase activity. Inhibition of this interaction by Gleevec triggered increased killing of intracellular M. Tb (56±14%) in six independent donors. Using a pH-dependent fluorochrome we demonstrate that increased antimicrobial activity is mediated by promotion of phagosomal acidification. As the ultimate effector mechanism we identify increased levels of the antimicrobial peptide cathelicidin (+39±15; n=4), which is cleaved from its inactive precursor to the bioactive form in the acidic environment.

Conclusion: Therapeutic inhibition of abl tyrosine kinase during leukemia treatment should not predispose to infections with intracellular pathogens and may even result in triggering antimicrobial effector mechanisms of innate immunity.

Gewinner des Science-Preises der DGP 2009