280 H. S. LAWRENCE ET AL. 



fact that leucocytes or extracts obtained from human peripheral 

 blood have been found incapable of transferring the capacity for 

 detectable serum antibody formation in agammaglobuhnaemic 

 subjects (Good et al, 1957) and in normal recipients at the time of 

 maximal transferred delayed sensitivity to diphtheria toxoid, 

 v^hen assayed by a most sensitive means of detecting antibody, 

 even in minute concentration (<o*oi mg./ml.) (Lawrence and 

 Pappenheimer, 1956). (3) The function transferred by leucocyte 

 extracts to human recipients consists of both the prompt effector 

 reagent of delayed allergy (e.g. prompt effects of local transfer of 

 homograft sensitivity) and the machinery necessary for its con- 

 tinued production in the recipient as in the leucocyte donor (e.g. 

 enduring effects of systemic transfer in recipients homografted one 

 to two weeks after injection of leucocyte extracts). 



The fmdings in respect of leucocyte extracts allow application 

 of principles elucidated in relation to delayed sensitivity of bac- 

 terial and fungal origin towards an understanding of mechanisms 

 of homograft sensitivity. In this perspective transfer factor may 

 be viewed as a common efferent instrument of tissue damage 

 encountered in the delayed type of altered tissue reactivity 

 whether this event is initiated by bacterial cells, by fungal cells, or 

 by cells of yet another type such as are found in tissue homografts. 



Summary 



The transfer of local or systemic skin homograft sensitivity 

 (accelerated rejection) in humans can be accomphshed with 

 DNAse-treated blood leucocyte extracts when obtained from 

 donors sensitized in an adequate fashion. The sensitivity trans- 

 ferred can be shown to be both prompt and enduring. Active 

 hypersensitization of leucocyte donors by repeated sequential 

 graft application may be accompanied by desensitization of the 

 donor to the graft and desensitization of donor leucocytes, 

 resulting in failure to transfer sensitivity. 



In adapting the highly sensitive transfer system in human species 



