HOMOGRAFT SENSITIVITY IN HUMAN BEINGS 277 



The role of desensitizadon 



The finding that leucocyte extracts obtained from one donor at 

 the height of his accelerated rejection period of a fourth-set 

 sensitizing skin homograft transferred homograft sensitivity 

 (accelerated rejection) to tv^o recipients is of some interest. Of 

 particular significance, hov^ever, was the finding that leucocyte 

 extracts prepared from the same donor ii days later were in- 

 capable of transferring homograft sensitivity to four additional 

 recipients. When the donor of leucocyte extracts was tested with 

 the apphcation of a fifth-set graft of the skin to which he had been 

 sensitized, he accorded it a first-set reaction of rejection. It may be 

 of interest also that the same leucocyte donor exhibited a "recall 

 flare" at each previously rejected graft bed site while in the course 

 of rejecting the second, third and fourth-set grafts (cf. Rapaport 

 and Converse, 1957). 



One interpretation of these results could be that the individual 

 actively sensitized by repeated application of skin homografts has 

 his peripheral blood leucocytes only transiently endowed with the 

 capacity to transfer homograft sensitivity. Another, perhaps more 

 likely interpretation, particularly in view of the appearance of the 

 "recall flare" phenomenon, would suggest that in the course of 

 active //ypersensitization of the leucocyte donor, the phenomena of 

 sensitization and Jesensitization proceed pari passu. If this be the 

 case, then when sensitization is in the ascendancy transfer will be 

 successful, and when desensitization has occurred transfer of 

 homograft sensitivity will fail. 



There is precedent for this conclusion in the transfer of tuber- 

 culin sensitivity in human beings where it has been found that 

 in vitro incubation of sensitized viable leucocytes with antigen 

 (tuberculin-PPD) results in their becoming desensitized and in- 

 capable of transferring sensitivity (Lawrence and Pappenheimer, 

 I957)« This observation has been confirmed in vivo in human sub- 

 jects by showing that leucocytes of donors sensitive to tuberculin 



TRANS. — 10 



