Legionella pneumophila down-regulates MHC class I expression of human monocytic host cells and thereby inhibits T cell activation

Neumeister, B.; Faigle, M.; Spitznagel, D.; Mainka, A.; Ograbek, A.; Wieland, H.; Mannowetz, N.; Rammensee, H. -G.

Legionella pneumophila down-regulates MHC class I expression of human monocytic host cells and thereby inhibits T cell activation

2005

Legionella (L.) pneumophila, the causative agent of Legionnaires’ disease, is an intracellular pathogen of alveolar macrophages that resides in a compartment displaying features of endoplasmatic reticulum (ER). In this study, we show that intracellular multiplication of L. pneumophila results in a remarkable decrease in MHC class I expression by the infected monocytes. During intracellular multiplication, L. pneumophila absorbs ER-resident chaperons such as calnexin and BiP, molecules that are required for the correct formation of the MHC class I complex. Due to reduced MHC class I expression, stimulation of allogeneic blood mononuclear cells was severely inhibited by infected host cells but cytotoxicity of autologous natural killer cells against Legionella-infected monocytes was not enhanced. Thus, reduced expression of MHC class I in infected monocytes may resemble a new immune escape mechanism induced by L. pneumophila.

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