DISCUSSION 



Kandutsch: As I understand it, your antigenic material isolated from 

 ascitic fluid is a cell product and is insoluble or particulate. When you 

 do agar gel diffusion tests with this and get a Ime, how do you exclude 

 the possibility that your insoluble antigen has simply not left the cup, 

 and that the line you see is due to an impurity ? I ask this because when 

 we attempted to carry out similar gel diffusion tests with our enhancing 

 (or "promoting") preparations we found that we had a Hne with the 

 rabbit antiserum (sometimes two) until I got the preparation as pure as 

 I was able to get it, and then we got no lines. The material just re- 

 mained in the cup in the system we used. 



Davies: We cannot rule out completely the possibility that the anti- 

 gen remains in the cup and that the line is due to impurity. However, 

 when we worked with bacterial antigens we found that the most 

 apparently insoluble substances would still give a diffusion line if you 

 waited long enough; there we had other evidence that the bacterial 

 antigen itself was responsible for the line. There is not as good evidence 

 here, but our method of estimating this activity is by dilution on diffu- 

 sion plates, and the amount of reaction we get with this product of 

 mine is as good as the best preparation of Dr. Haughton's species- 

 specific ** antigen 3 ". So it must represent a fairly large proportion of 

 this product. By all the means we have tried so far we have not been 

 able to pick up impurity, but our evidence for physical homogeneity is 

 rather poor. 



G. Klein: Since you are using an isologous ascitic tumour system, I 

 wondered whether it is really certain that the H-2 antigens come from 

 the tumour cells rather than from the host, since the fluid is coming 

 from the host. Perhaps you could clarify this by using an ascitic tumour 

 homograft which does grow in spite of homograft reaction in a non- 

 specific fashion. There are such tumours available. 



Davies: The analogous product of a non-specific tumour didn't give 

 any inhibition at all in the tests I showed. Full details are given in the 

 published version of my paper. However, with one supposedly non- 

 specific tumour (LAN) recently we have found that it does carry some 

 specificity — it inhibits in H-2'' and H-2^ So this is rather interesting 



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