Am. J. Respir. Crit. Care Med.,
Volume 157, Number 6, June 1998, 1967-1974
Entry and Intracellular Growth of Legionella dumoffii in
Alveolar Epithelial Cells
KOJI
MARUTA,
HIROSHI
MIYAMOTO,
TETSUO
HAMADA,
MIDORI
OGAWA,
HATSUMI
TANIGUCHI,
and
SHIN-ICHI
YOSHIDA
Departments of Microbiology and Pathology and Cell Biology, School of Medicine, University of Occupational and
Environmental Health, Kitakyushu, Japan
We have found that Legionella dumoffii strain Tex-KL (ATCC 33343) invades into and proliferates in
the human lung alveolar epithelial-cell line A549 in vitro. The organism associated with the A549 cells
at a 10-fold greater magnitude than L. pneumophila Philadelphia-1 during in vitro coculture for 1 h.
Thereafter, L. dumoffii Tex-KL invaded the cells at a significantly higher rate (100- to 1,000-fold) than
did L. pneumophila Philadelphia-1. After internalization, however, both bacteria proliferated at the
same rate. This in vitro finding led us to examine the bacterial localization in lungs in a fatal case of
L. dumoffii pneumonia. Double immunostaining revealed the bacteria in surfactant apoprotein A-positive cells (i.e., type II alveolar epithelial cells). Next, we infected guinea pigs intratracheally
with L. dumoffii Tex-KL. The animals became sick with a fever from 24 h to 48 h after infection with
104 to 109 cfu of L. dumoffii Tex-KL. The lung tissues were examined through electron microscopy at
definite intervals. Many bacteria were found not only inside phagocytic cells in the alveolar space, but also in type I and type II alveolar epithelial cells. These findings strongly suggest that L. dumoffii
has an ability to invade into and proliferate in human alveolar epithelial cells, which may explain the
rapid and fulminant progress of pneumonia caused by L. dumoffii.
