IMMUNOLOGICAL COMPETENCE OF SMALL LYMPHOCYTES 25I 



tively reflect the occurrence of graft-versus-host reactions in this 

 system. 



Histopathological changes in tissue sections from these animals 

 may be summarized as follows. The white pulp folHcles of the 

 spleens of normal A/Jax mice are compact with definite peri- 

 follicular*' collars", but the follicles of runts were more diffuse and 

 hypertrophied with indistinct perifoUicular "collars". Moreover, 

 the red pulp of runts showed far more pale-staining and swollen 

 reticuloendothehal cells as well as accentuated erythropoiesis. In 

 contrast with litter mate controls, enlarged Hvers of runts showed 

 oedema and focal necrosis with vacuolation and loss of cytoplasm 

 in hepatic cells. In other areas, coalescence of cells with indistinct 

 cytoplasmic membranes was observed. No marked changes were 

 seen in sections of enlarged kidneys from runted animals. 



Non-tolerant and non-chimeric state of inoculated 

 survivors 



Most of the experimental animals that failed to die of acute 

 transplantation disease (cf. Table I) were test-grafted with 

 C57BL/6 female skin at six to ten weeks of age. Littermate 

 controls were similarly test-grafted at the same time. All of these 

 homografts were rejected between 8 and 12 days after grafting, 

 indicating that none of the A/Jax mice neonatally injected with 

 C57BL/6 small lymphocytes had been made tolerant of C57BL/6 

 antigens. The absence of accelerated reactions to these homo- 

 grafts also indicated that the experimental A/Jax mice had acquired 

 no lasting immunity as a consequence of neonatal exposure to 

 C57BL/6 lymphocytes. In another approach to the question of 

 tolerance or persistence of donor cell descendants, an attempt was 

 made to renew the runting syndrome in animals that had 

 recovered from the initial graft-versus-host reaction. Eleven such 

 survivors about 12 weeks old that had not been tested with skin 

 homografts were each injected intravenously with 3*4 million 

 adult C57BL/6 blood lymphocytes. None showed any signs of 



