40 DISCUSSION 



may sometimes give tolerance and we are convinced that this is due to 

 contamination of our red cell preparations with leucocytes. We are, 

 therefore, of the opinion that tolerance of skin cannot be induced with 

 erythrocytes in mammals. 



Brent: Dr. Owen and I thought that the inabihty of red cells to 

 sensitize might be because the red cell antigen requires adjuvant, and 

 some years ago we investigated this possibility. We completely failed 

 to get any sensitization against skin grafts with red cell-adjuvant 

 emulsions. Dr. Barrett, have you repeated the experiments which you 

 did originally with tumour tissues using skin grafts ? 



Barrett: I have not, but Dr. Breyere has used some preparations in 

 rats and tested them with skin grafts. Regrettably, his red cell pre- 

 parations cannot be said to be certainly clear of leucocytes, although we 

 can be sure that there aren't a great many leucocytes because of multiple 

 handlings in unsihconized glass in the preparation of the antigen. 

 However, the result he gets is compatible with the red cell dose and not 

 compatible with the probable white cell dose. 



BiUingham: Drs. D. Steinmuller and L. Weiner have recently found 

 that injection of a suspension containing as few as 100,000 homologous 

 B.N.-strain spleen cells into adult Lewis rats, weighing about 200 

 grams, will sensitize them in respect of B.N. test skin homografts 

 transplanted 8 days later. 



To return to the point raised by Dr. Mitchison: we have all tried, by 

 various methods, to determine whether or not transplantation antigen 

 specificity is present on red cells. One procedure that we are currently 

 investigating takes advantage of the fact that the homograft sensitivity 

 eUcited by intraperitoneal^ inoculated splenic cells in mice dies away 

 fairly rapidly. Inoculation of homologous red cells, or lyophilized 

 tissues, should reawaken homograft sensitivity in these animals if they 

 contain the appropriate antigenic configurations. 



Mitchison: I have no difficulty in procuring tolerance of skin grafts in 

 chickens using red cells in irradiated blood; provided that the animal is 

 tolerant of the red cells it seems usually to be tolerant of the skin graft. 

 There are some technical complications about contamination of red 

 cells by leucocytes, but I don't think that the irradiated leucocytes were 

 responsible for the tolerance. I would like to ask Dr. Hasek whether the 

 compatibility of chromium-labelled red cells from the male in the 



