Role of the 25 kDa major outer membrane protein of Legionella pneumophila in attachment to U-937 cells and its potential as a virulence factor for chick embryos

The gene encoding the 25 kDa major outer membrane protein (MOMP) of Legione lla pneumophila was transformed into Escherichia coli JM 83 and the resulta nt E. coli LP 116 clone expressed the Legionella-MOMP. Compared with the pa rent E. roll strain, the clone showed a fivefold increase in opsonin-indepe ndent binding to U-937 cells. Furthermore, this gene was incorporated by el ectroporation into a low virulence derivative of Leg. pneumophila which sho wed reduced expression of the MOMP but enhanced expression of a 31 kDa prot ein in the OMP profile. After electroporation, the attenuated strain showed an increased expression of the MOMP while the 31 kDa protein was eliminate d and virulence for the chick embryo was re-established. The use of a monoc lonal antibody specific for the MOMP abolished virulence and adherence. The se studies suggest that the 25 kDa MOMP of Leg. pneumophila serves as an ad hesive molecule for host cells and that this protein plays a major role in the virulence of the organism for the chick embryo.