108 The Lymphocyte and Lymphocytic Tissue 



donors. Four days later the ipsilateral popliteal lymph nodes were obtained 

 linn) the leukocyte-injected rabbits, and cells obtained from these were 

 transferred to the prospective recipients of the experiment. At the same 

 time lymph node cells were obtained from the original donors of the blood 

 leukocytes. The latter were incubated in vitro with Shigella antigen, washed, 

 and transferred to the recipient animals. On subsequent determination of 

 the antibody titers of the recipient rabbits, it was found that those that had 

 received the cells from lymph nodes draining sites of injection of rab- 

 bit leukocytes showed mean anti-Shigella agglutinin titers which were only 

 approximately one seventh those of the control animals, which had been 

 given only the Shigella-incubated lymph node cells. Other control groups 

 of recipients showed anti-Shigella agglutinin titers in the usual elevated 

 range. These included recipients in which the "anti-leukocyte" lymph node 

 cells had been heated before transfer and included still others given cells 

 from lymph nodes contralateral to the sites of rabbit-leukocyte injection. 43 



SUMMARY 



It can be seen that the involvement of cells of the lymphocytic series, or of 

 the lymphatic system, in the host response to transplanted tissue has been 

 indicated by observations made in three types of studies: (1) studies of 

 cellular infiltrations of transplanted tissue, (2) examinations of the cellular 

 reactions in lymph nodes regional to tissue transplants, and (3) studies of 

 the transfer of transplantation immunity by lymph node cells. The precise 

 function of the various cell types within this system in the rejection of trans- 

 planted tissue is not understood, and many questions remain unanswered 

 in this area. For example, is the presence of lymphocytes at the site of a 

 homograft, and especially in contiguity with transplanted cells, an expres- 

 sion of hypersensitivity, or a means of delivering antibodies, or do these cells 

 serve some other function in this situation? Again, in suspensions of trans- 

 ferred lymph node cells, which of the cell types are effective in conferring 

 transplantation immunity? If the majority cell type found in the transferred 

 suspensions is involved, does it carry out its function in the form in which 

 it is transferred or after conversion to another cell type in the new host 

 tissue, and by what mechanism is the tissue transplantation immunity con- 

 ferred? The answers to some of the questions in this area will come from 

 the considerable efforts being expended at present on immunologic study 

 of these problems. However, a great contribution to this field will be made 

 by the clarification of the interrelations among cell types within the lym- 

 phatic system — a clarification that must result from studies by cytologists 

 and pathologists. 



