IMMUNOLOGICAL COMPETENCE OF SMALL LYMPHOCYTES 245 



However, in one litter all animals which were successfully injected 

 with 2* 5 million lymphocytes died of typical runt disease. In all 

 of these experiments, one or two mice in each htter were left as 

 uninjected controls identified by cutting off the tail tips; these 

 animals showed normal growth and survival. 



Following the injection of one miUion lymphocytes by the 

 intracardiac route into neonatal mice >24 <48 hours old, none 

 of the mice showed evidence of runt disease and all developed 

 normally. Thus rapid maturation of the A/Jax host's immune 

 response capacity within two days after birth apparently led to 

 the elimination of homologous donor lymphocytes before any 

 visible damage was done. 



Peripheral blood lymphocytes from specifically preimmunized 

 C57BL/6 mice were tested to evaluate further the immunological 

 competence of these cells on a quantitative basis. Small lympho- 

 cytes were harvested as in earlier experiments from adult C57BL/6 

 mice immunized by two intraperitoneal injections each of cells 

 equivalent in amount to J adult A/Jax spleen at 13 and 6 days 

 previously. A/Jax mice from four litters less than 24 hours old 

 were injected with about 900,000 "immune" lymphocytes — 

 equivalent to a dose of normal lymphocytes just sufficient to 

 procure runt disease. To avoid immediate reactions that could be 

 attributed to preformed donor serum antibodies, the cells were 

 washed repeatedly in cold Hank's solution prior to injection. All 

 18 recipients were severely affected and 14/18 died of acute runt 

 disease between seven and 20 days of age. The MST's of 10 -8 

 (9 '2-1 2* 7) days or 13 • i (10 • 5-16*4) days on the assumption of a 

 truncated distribution clearly reveal that sensitized lymphocytes 

 are capable of mediating accelerated transplantation disease 

 (cf Table I). The efficacy of such cells even in relatively low 

 dosage is also attested by the fmding that no animal escaped 

 immunological attack. 



The apparent absence of pathological changes in certain animals 

 under conditions where the majority of animals receiving the same 



TRANS. — 9 



