A sensitive cell line, HL cells, for isolation and propagation of Chlamydia pneumoniae strain TWAR.

The sensitivity of a human line, HL cells, for growth of Chlamydia pneumonia was compared with HeLa 229 cells using laboratory-adapted and wild strains. HL cells were more sensitive for growth of HeLa-adapted C. pneumoniae strains and more sensitive for isolation of the organism from patient specimens. Adaptation of new isolates to continuous cell culture growth has been much more successful in HL cells. Centrifugation of inoculum and incorporation of cycloheximide in the medium enhanced the infectivity. Microscopic observation of cultures from days 2 to 6 showed that C. pneumoniae undergoes a second cycle of growth in HL cells. However, the optimal time of harvesting is 3 days after inoculation.