The biology of Coxiella burnetti and the pathobiochemistry of Q fever and its endotoxicosis

Abstract

C. burnetii possesses a battery of host-independent enzymes which mediate endergonic and exergonic reactions. The biochemical and biophysical lesions responsible for the organism's obligate intracellular parasitic state have not been identified. Clues to this fundamental problem may lie in the agent's acidophilic metabolism and proliferation within the host cell's phagolysomal vacuole. What are the modifiers of transcription and translation? What constituents of the lysosomal vacuole contribute to the parasite's metabolism? Does the parasite have intrinsic cell-wall synthesizing capability? The isolation of plasmids from C. burnetii opens lines of investigation which should lead to solution of the problem, thereby helping to answer the general question of what is the nature of obligate parasitism. An understanding of the pathobiochemistry of Q fever and of its endotoxicosis rests on elucidating closely interrelated regulatory events. Stimulated hepatic transcription and translation of certain RNA and protein species attend the development of the disease, as do phosphorylation and dephosphorylation of central RNA and protein species. Phosphorylation and dephosphorylation are central regulators in protein synthesis. Whole animal experiments differ from those with cultured cells in important responses. Glycogenolysis, hepatic steatogenesis, and lipase activation are obvious examples of such differences. Stimulation of the production of lymphokines and of hormones is absent in HepG2 cells, and insulin seems to be critical in regulating the phosphorylation-dephosphorylation equilibrium which leads to regulation of protein synthesis. Newly synthesized, so far unidentified proteins may be involved in convalescence, re-establishing the homeostasis of the uninfected state. The model of pathobiochemical regulation in Q fever and endotoxicosis may be applicable to other febrile infections and endotoxicoses.