24 DISCUSSION 



one. You certainly can't extrapolate from the mouse to any other 

 species ; this coincidence of histocompatibility antigens on the red cell 

 and on the other tissue cells is purely fortuitous. 



Woodruff: Is it fortuitous ? Is there any evidence that this is purely a 

 mouse phenomenon ? 



Amos: I don't know if I can answer that completely. Dr. Bilhngham, 

 in the rat, how many of these other systems also show up with 

 haemagglutinating antibodies ? 



Billinghani: From our analyses with the unrelated B.N. and Lewis rat 

 strains we know that there are at least i6 different histocompatibihty 

 loci in this species, of which 4 appear to be of major status (Billingham, 

 R. E., Hodge, B. A., and Silvers, W. K. [1962]. Proc. nat. Acad. Sci. 

 {Wash.), in press). Dr. Joy Palm has recently reviewed the current 

 status of knowledge of blood groups in the rat ("Blood Groups in 

 Infra-Human Species," in Ann. N.Y. Acad. Set., 1962, in press). In her 

 own studies with the Lewis and B.N. strains she has found that genes 

 of at least one blood group locus are important in determining the 

 incompatibility of skin homografts. 



G. Klein: Dr. Amos, is your statement that the coincidence of trans- 

 plantation antigens on the red cells and on other tissue cells is purely 

 fortuitous, based mainly on the fact of haemagglutination ? Could it be 

 that most antigens are in fact present on red cells but some of them are 

 unable to cause haemagglutinability ? 



Amos: I don't think so; this is a quantitative question. I can answer 

 this in an indirect way in terms of absorption, that there is a completely 

 different pattern of absorption obtained with some of the non-H-2 

 antibodies. Certainly the quantitative differences in the amounts of 

 antigens are quite different with respect to different antigens. Within 

 the H-2 system the distribution of antigens appears to be much the 

 same, so that for any given organ, no matter whether it is H-2^, H-2^, 

 H-2^, etc. the level as judged by absorptive capacity is comparable. But 

 if you now move to a system other than H-2, the relative proportion of 

 antigens in different tissues will be quite different, e.g. alpha, which is in 

 high concentration in kidney while H-2 is low in this organ. I think 

 this relationship is different again for H-i and H-3. This is why I think 

 it is rather fortuitous. It is a question of the activity of the genes con- 

 trolling the particular tissue that you're dealing with. 



