Chemotactic response of fish macrophages to Legionella pneumophila: correlation with pathogenicity

Abstract

Chemotaxis is the directional migration of cells in response to a chemical stimulus. This phenomenon appears to be responsible for the accun~ulation of macrophages during inflammation This work represents an attempt to understand certain aspects of host-parasite relationships in Legionnaire's Disease. In the first phase of this study, we measured the chemotactic stimulation of fish macrophages by 2 strains of Legionella pneumophila, one virulent and one avirulent for guinea pigs. Results from this part of the study, coupled with the possibility that reduced chemotaxis may b e a factor contributing to increased virulence, led us to initiate the second phase of this work to determine the correlation between in vitro chemotaxis and the degree of virulence of L. pneumophila for spot Leiostonius xanthurus. These studies demonstrated that virulent cells did not attract n~acrophages to the extent that avirulent cells did. The percentage of macrophages migrating toward virulent Legionella at 90 min was 24 as compared to 61 for the avirulent strain. In vivo studies showed that intraperitoneal injection of 1 to 2 X 10'' viable cells of vlrulent L. pneumophjla killed 100 ":, of the fish within 2 d whereas the same number of avirulent L pneumophila resulted in death in only 58 '10 of the fish within 2 d after injection.