STUDIES ON TRANSPLANTATION ANTIGENS I5 



tions, and we have therefore examined the effect of hpid solvents 

 on the sensitizing activity of dried antigenic sediment. Aqueous 

 suspensions of antigenic sediments v^ere shell-frozen at — 79°, 

 "lyophiUzed" at a temperature not exceeding —5°, and then 

 further dried over phosphorus pentoxide at room temperature 

 overnight under high vacuum (Brent, Medawar and Ruszkiewicz, 

 1 961). From eight determinations, the weight of antigen dried 

 under these conditions was 9*9 ± 0-6 mg. per gram wxt weight 

 of the lymphoid tissue from which the antigen was extracted. 

 The dried antigen was extracted successively, at 0° or —15°, in 

 3:1 v/v ethanol-ether, 3 : i v/v ether-carbon tetrachloride, 

 ethanol-ether as before, and ether. The solvents of each extraction 

 were pooled, and the lipid emulsified in water either (i) by 

 evaporating to dryness, redissolving in ethanol, adding water, and 

 withdrawing alcohol on a rotary evaporator below room 

 temperature; or (2) by adding water to the pooled extract and 

 removing the organic solvents with a rotary evaporator as 

 before — a simpler and more effective procedure. 



The residue after exposure to lipid solvents was simply redis- 

 persed in normal saline, in which part of the protein now formed 

 a clear solution. 



The lipid fraction was tested for its sensitizing power, and the 

 residue for its sensitizing power and its ability to absorb the 

 corresponding haemagglutinins (see Brent, Medawar and Rusz- 

 kiewicz , 1 961). The results of the tests in vivo are summarized in 

 Table IV. The lipid fraction was inert, in the sense that the skin 

 grafts used to disclose any state of sensitivity it might have 

 produced enjoyed a normal expectation of life (~ 11 days). 

 The residue had no power to absorb humoral antibodies, 

 but retained a small but clearly discernible fraction of its 

 power to sensitize. Recombination of the lipid extract with 

 the residue gave the same results as the use of the residue 

 alone. These facts are commented upon at the end of the next 

 section. 



