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Murine Typhus Toxin: Studies on Identification of the Neutralizing Factor Present in Normal Human Serum

National Institute of Allergy and Infectious Diseases, Rocky Mountain Laboratory, Hamilton, Montana 59840

ABSTRACT

Studies were made on the isolation and identification of the Rickettsia typhi toxin-neutralizing factor (TNF) previously demonstrated in normal human serum. By means of various methods of separating serum proteins, such as filtration on Sephadex G-200, dextran precipitation, hydroxyapatite chromatography, and ultracentrifugation, TNF was found to be closely associated with purified serum ß-lipoprotein, although no serological relationship with this protein was demonstrated. Lipase as well as trypsin digestion of purified preparations of ß-lipoprotein destroyed the TN activity. No evidence was obtained for an association of TNF with the immunoglobulins or with any serum protein other than ß-lipoprotein. Further studies revealed that (i) serum specimens with TN titers of 1:1024 and others with titers of 1:8 or less contained the same concentration of ß-lipoprotein; (ii) purified preparations of ß-lipoprotein isolated from TNF positive and negative sera, and which had the same protein concentration, differed as much as 250-fold in TN titer; and (iii) the TN activity of a serum could be removed by absorption with antiserum to ß-lipoprotein from a positive donor, but not with antiserum to ß-lipoprotein from a negative donor.