Requirements for ingestion of Chlamydia psittaci by mouse fibroblasts (L cells)

Abstract

Ingestion of 14C-amino acid-labeled C. psittaci (6BC) by mouse fibroblasts (L cells) was inhibited when the host cells were incubated for 30 min at 37.degree. C in Earle salts containing 10 .mu.g of crystalline trypsin/ml. Tryptic digestion also inhibited the ingestion of 1-.mu.m polystyrene latex beads. Trypsin-treated L cells almost completely recovered their ability to ingest chlamydiae after 4 h at 37.degree. C in medium 199 with 5% fetal calf serum. Cycloheximide (10 .mu.g/ml) blocked this recovery. Heating 14C-amino acid-labeled C. psittaci for 3 min at 60.degree. C inhibited its ingestion by L cells; inactivating it with UV light did not affect the ingestion rate. Efficient ingestion of C. psittaci by L cells involves trypsin-labile sites on the host and heat-sensitive sites on the parasite. The failure of excess unlabeled infectious C. psittaci to promote the ingestion of 14C-labeled heat-inactivated chlamydiae suggests that direct interaction between these 2 sites must occur for uptake to proceed normally.