AN ISOANTIGENIC LIPOPROTEIN 77 



dying at a given dose varied among experiments. Such variation 

 in the dose of antigenic material required to produce enhancement 

 has been observed throughout these studies and is presumably due 

 chiefly to variations in the growth characteristics of the tumour. 

 When the ascites form of sarcoma I was used as the challenging 

 graft, the amount of antigenic material required to produce 

 enhancement was considerably less than when the solid form of 

 the same tumour was used. However, the use of the sohd tumour 

 afforded better quantitation of antigenic activity. In a number of 

 enhancement assays, the whole Triton extracts and the TSL 

 fraction were at least as active as the particulate fraction from 

 which they were derived and in some experiments they appeared 

 to be considerably more active on a weight basis. Results com- 

 parable to those shown in Table I were obtained with the 

 haemagglutination inhibition assay except that the whole Triton 

 extract appeared to inhibit only slightly. Possibly the haemagglu- 

 tination inhibition assay provides a more quantitative picture of 

 the distribution of activity since the TSL fraction which contained 

 most of the antigenic activity constituted only about 1 5 per cent 

 of the whole Triton extract. 



Because of the low levels of activity present in the water- 

 soluble fraction of the Triton extract and its complexity — at least 

 eight components were indicated by chromatography on diethyl- 

 aminoethyl (DEAE)-cellulose columns — further studies were 

 concentrated on the Triton-soluble lipoprotein. 



Properties of the Triton-soluble lipoprotein 



Different preparations of freeze-dried TSL were powders 

 ranging in colour from tan to brown. It dissolves readily in 

 a I per cent solution of Triton at pH 7 or above, in concentrations 

 as high as 80 mg./ml., to give an optically clear solution. 



Electrophoresis: Some electrophoretic patterns obtained with a 

 Tisehus apparatus are shown in Fig. 3. Triton was included in 



