A domino-like chlamydial attachment process: concurrent Parachlamydia acanthamoebae attachment to amoebae is required for several amoebal released molecules and serine protease activity

Abstract

A domino-like chlamydial attachment process: concurrent Parachlamydia acanthamoebae attachment to amoebae is required for several amoebal released molecules and serine protease activity Parachlamydia acanthamoebae is an obligate intracellular bacterium that infects free-living amoebae (Acanthamoeba), and is a potential human pathogen associated with hospital-acquired pneumonia. The attachment mechanism of this bacteria to host cells is crucial in bacterial pathogenesis, yet remains undetermined. Hence, we obtained monoclonal antibodies (mAbs) specific to either P. acanthamoebae or amoebae in an attempt to elucidate the attachment mechanism involved. Hybridomas of 954 clones were assessed, and we found that four mAbs (mAb38, mAb300, mAb311, mAb562) that were reactive to the amoebae significantly inhibited bacterial attachment. All mAbs recognized amoebal released molecules, and mAb311 also recognized the amoebal surface. mAbs reacted with the bacteria not only within amoebae, but also when they were released from amoebae (except mAb311). Furthermore, a serine protease inhibitor had an inhibitory effect on the bacterial attachment to amoebae, although none of the mAbs had any synergistic effect on the inhibition of attachment by the protease inhibitor. Taken together, we conclude that concurrent P. acanthoamebae attachment to amoebae is required for several amoebal released molecules and serine protease activity, implying the existence of a complicated host-parasite relationship. INTRODUCTIONChlamydiae, which are obligate intracellular bacterial pathogens, have been reclassified into the order Chlamydiales, which includes four families, Chlamydiaceae, Parachlamydiaceae, Waddliaceae and Simkaniaceae (Horn, 2008). The family Chlamydiaceae, which is broadly distributed among mammals, including humans, includes two major human pathogens designated the pathogenic chlamydiae. Chlamydophila pneumoniae is a causal agent of common respiratory infection (Bartlett, 2008) and is also suspected of being involved in certain chronic diseases, such as asthma (Sutherland & Martin, 2007) and atherosclerosis (Watson & Alp, 2008), while Chlamydia trachomatis is responsible for sexually transmitted disease and preventable blindness (Jordan et al., 2011). Furthermore, Parachlamydiaceae, Waddliaceae and Simkaniaceae have only recently been recognized as environmental chlamydiae, and exhibit a wide distribution in natural environments, such as in rivers and soil (Greub, 2009;Horn et al., 2004). These species can grow and survive within the free-living amoeba Acanthamoeba, which is the most abundant genus of amoebae (Khan, 2006).Abbreviations: AIU, amoeba-infectious units; HRP, horseradish peroxidase; PAS, Page's modified Neff's amoeba saline.A supplementary table, showing a summary of monoclonal antibodies directed to either P. acanthamoebae or amoebae, is available with the online version of this paper. Microbiology

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