STUDIES ON TRANSPLANTATION ANTIGENS 7 



preparations then (1957) in use. At all events, the antigenic 

 preparation of Billingham, Brent and Medawar (1958) can absorb 

 humoral antibodies in vitro and excite their formation in vivo 

 (Brent, Medawar, and Ruszkiewicz, 1961). The preparation 

 described by Herzenberg and Herzenberg (1961) — probably 

 similar to, but anatomically better defmed than our own — and the 

 highly active preparation which Davies will describe shortly 

 (see Davies and Hutchison, 1961) also absorb or inhibit the action 

 of humoral antibodies; both have been subjected to scrupulous 

 tests of specificity of action, and we await with great interest tests 

 of their power to sensitize. Furthermore Lejeune and Kandutsch 

 (this vol. p. 25 and 72) both make use of the specific serological 

 activity of their sensitizing or "enhancing" extracts, and Stetson's 

 analysis (unpublished) of the anatomical distribution of iso- 

 antigens within cells is founded upon their power to inhibit 

 haemagglutination or the action of cytotoxins. The serological 

 activity of tissue extracts with respect to the H-2 system of antigens 

 in mice is therefore established beyond doubt. As our own work 

 has just been published (Brent, Medawar and Ruszkiewicz, 1961) 

 we shall not recapitulate it here. 



Instead, we shall discuss three topics under the general heading 

 of studies on the physical and chemical properties of extracts 

 containing sensitizing antigens : (i) problems connected with the 

 solubility or solubilization of antigens; (2) the behaviour of 

 cellular extracts subjected to the action of lipid solvents; and (3) 

 the heat-stability of sensitizing antigens. 



In nearly all our experiments (exceptions are noted) we have 

 used A-strain mice as donors of antigenic matter and of grafts, and 

 CBA or C3H mice as their recipients. It is known of CBA mice 

 (Barnes and Krohn, 1957), and can be assumed of C3H mice, that 

 they differ from A-strain mice by antigens segregating at ten or 

 more loci, but the serological and sensitizing activities we 

 describe are dominated by "strong" antigenic differences at the 

 H-2 locus. 



