DISCUSSION 67 



that it grows so readily in all kinds of mice, in some cases in the pre- 

 sence of this incompatibility. However, for syngeneic specific tumour 

 systems, the yield of purified antigen is related to the weight of cells 

 recovered from the fluid, and not to the weight of material remaining 

 in the fluid after the cells have been removed. 



G. Klein: If the antigens come from the tumour cells, then the 

 question is whether they are released due to lysis or by secretion. This 

 could perhaps be clarified by using different ascitic tumours that have 

 very different tendencies to lyse. If it could be shown that it is not lysis 

 but secretion, it may be very interesting to find out whether different 

 types of tumour cells show differences in their secretory ability. 



Hasek: I am inclined to believe that it is lysis. V. Haskova and I. 

 Hilgert (1961. Folia hiol. (Prague), I, 81) have some evidence of in- 

 creasing content of deoxyribose in the ascitic fluid with the growth of 

 the tumour used in their experiments (sarcoma I) which might reflect 

 the cell disintegration. 



Davies: In my fractionation traces of nucleic acid are removed, but 

 Hilgert's correlation of DNA increase with greater antigenic potency is 

 very suggestive of the antigen being a product of cell lysis. We also 

 find a relatively greater yield of antigen from leukaemic cells, which 

 are much more easily lysed than the other kinds of ascites cells we have 

 used. If the lysis could be increased we might get a much better yield 

 of antigen, but complete cell disruption is to be avoided because the 

 starting material is then so much more complex. 



Simonsen: I should be very interested to know where this soluble 

 antigen of ascitic fluid would go in the isogenic host. Is it possible to 

 label it with some radioactive label so that you can see what happens to 

 it when no antigenic disparity is involved ? Where does it go to, and 

 what is the lifespan of this material when there is no antibody reaction 

 against it ? 



Davies: We worked out that it would be prohibitively expensive to 

 label with ^*C by feeding the mice, but it might be possible with ^^P. 



Brent: You mentioned that you obtained haemagglutination inhi- 

 bition with 50 (JLg. of material per ml. of antibody. I wasn't quite clear 

 about the strength of the antibody used. 



Davies: No, 50 [xg. is the amount of material which will inhibit in the 

 smallest number of haemagglutinating doses which we dare to use 



