Rickettsia rickettsii growth and temperature-inducible protein expression in embryonic tick cell lines

Rickettsia rickettsii has limited adverse effects on its arthropod vector, but causes severe disease in man, To model differences in host-parasite interaction, R. rickettsii growth and protein expression were examined at temperatures reflective of host environment in the tide cell lines DALBE3 and IDE2, the human endothelial cell line ECV304, and the African green monkey kidney cell line Vero76. At low multiplicities of infection, rickettsial titres increased 10²-10³-fold in all cell lines after incubation for 3 days at 34°C, At higher multiplicities and with extended incubation, R. rickettsii showed enhanced survival in tick versus mammalian cells. No difference in rickettsial ultrastructure or protein profiles was detected between different host cell types. Rickettsial proteins of 42, 43, 48, 75 and 100 kDa are induced in tick cells shifted from 28°to 34°C, but not in cells maintained at 28°C. This temperature response may be associated with expression of rickettsial determinants that are pathogenic to mammalian hosts.