TRANSPLANTATION TOLERANCE AND AGE I47 



Table III 

 Spleen indices* of CBA mice killed 8 days after challenge with C57BL 



SPLEEN cells FOLLOWING NEONATAL INJECTION WITH ISOLOGOUS OR HOMOLOGOUS 

 LETHALLY irradiated CELLS 



(Data from Howard and Michie, 1962) 



Day o Day 2 



lo'i.v. + lo'i.P. 1*5 X lo'i.v. + 



irradiated 1-5 x 10' i.p. Test 4S1E Test 4S2E Average 



spleen cells non-irradiated 

 spleen cells 



CsjBL CBA Cs7BL 



+ o 0*94 0*92 0*93 



+ + i-io 0-85 0-97 



o + + I -60 2-31 1-96 



00 + 2-02 2-17 2-09 



• c 1 -A — rel. spleen wt. of treated mouse 



~ rel. spleen wt. of untreated litter-mate 



to the host. In this case no resistance was conferred. The overall 

 findings are summarized in Table IV. It can be seen that whenever 

 the initial inoculum and the challenging inoculum have an H-2 

 histocompatibility group in common which is lacking from the 

 host, the resistance phenomenon shows itself Whenever these 

 conditions are not met, no resistance is induced. If the resistance 

 results from specific sensitization of the newborn mice to strong 

 histocompatibility antigens of the challenge donor, then these 

 results would conform precisely to expectation. 



In a separate series, htters subjected at birth to the presumptively 

 immunizing procedure were left unchallenged and their spleens 

 were harvested on day 2 for histological examination. As com- 

 pared with uninjected or isologous-injected controls, these 

 showed an approximate doubling of mitotic rate, appearance of 

 numerous large pyroninophilic cells in the red pulp and the 

 emergence of foci of activated reticulum cells in the Malpighian 

 bodies. All these changes parallel closely those found in adults 

 following strong antigenic stimulation. 



Much remains to be done if the observed phenomena are fully 



