DE-NOVO SYNTHESIS OF LEGIONELLA-PNEUMOPHILA ANTIGENS DURING INTRACELLULAR GROWTH IN PHAGOCYTIC-CELLS

Legionella pneumophila is a gram-negative rod which is able to multipl y within phagocytic cells, The process of phagocytosis leads to a rapi d environmental change that might require a coordinate regulation of g ene expression to ensure intracellular survival, Since there is little information on up- and downregulation of genes during the early phase s of phagocytosis, we radiolabeled intracellular L. pneumophila at dif ferent times after phagocytosis by macrophages of the Mono Mac 6 cell line and immunoprecipitated antigens with anti-legionella sera or mono clonal antibodies, We could identify two antigens which were upregulat ed, one of which was the Mip protein, three antigens which were downre gulated, and three antigens which were not detectable in extracellular ly grown L. pneumophila. The Mip protein was stained most intensively 4 to 8 h after intracellular infection, suggesting that it is needed d uring intracellular multiplication rather than initiation of infection , A 44-kDa antigen which was not detectable during extracellular growt h was most prominent from 2 to 4 h postinfection when Mono Mac 6 cells were used as phagocytic cells, The 44-kDa antigen was also expressed during growth within Acanthamoeba castelanii, MRC-5, and U937 cells bu t with different kinetics, Synthesis of this antigen was not dependent on protein synthesis of the host cell, Since the 43-kDa antigen could be precipitated by an antiserum produced against a recombinant Escher ichia coli harboring a plasmid with an L. pneumophila insert which als o codes for the mip gene, we believe that the corresponding gene is wi thin the vicinity of the mip gene, We named this protein legionella in tracellular growth antigen (LIGA), since it could be found exclusively in intracellularly grown L. pneumophila.