SESSILE AND HUMORAL ANTIBODIES 221 



in the primary rejection of allogeneic skin grafts, we decided to 

 examine the possibility of synergic activity occurring between 

 humoral and cellular components in this context. To perform 

 such experiments one must know what dose of immune cells is 

 capable of a detectable effect per se, and then employ smaller 

 quantities. Attempts were made to titrate sensitized cells by 

 assessing the number needed to produce a well defmed adoptive 

 immunity against skin grafts. The experience of Bilhngham, 

 Brent and Medawar (1954) when demonstrating adoptive 

 immunity in CBA hosts against A skin indicated that at least four 

 immune nodes per recipient would be required; Mitchison (1955) 

 estimated that approximately fifty milhon sensitized cells were 

 the minimum number able to transfer a detectable level of 

 immunity to Sa i in CsyBR/a and C57BL hosts in his experi- 

 ments. Wiim (1961) has been able to observe evidence of adoptive 

 immunity to Sa i in C57BL/ 10 hosts with lower doses of sensitized 

 cells also administered intraperitoneally, and in contrast to the 

 other authors found the spleen possessed marked immune 

 activity as early as 7 days after implantation of the immunizing 

 graft, hi order to economize on our mouse stocks used for the 

 production of sensitized cells, we injected each animal at 6 

 subcutaneous sites in relation to the axillary, brachial and inguinal 

 lymph nodes and once intraperitoneally. Five days later the 

 spleen and lymph nodes were harvested, and pooled cell suspen- 

 sions prepared in " 199" medium. Donors of sensitized cells were 

 in all cases of the same strain and sex as the recipients. 



Comparisons between sensitized cell dosage experiments 

 performed by different investigators are fraught with difficulties. 

 In addition to the usual strain differences, there are the different 

 test systems of unequal sensitivity. The grafting of H-2 incom- 

 patible skin is a sensitive method of revealing immunity, but a less 

 delicate test for showing enhancement. The reverse may be true 

 of some tumour grafts, and marginal degrees of enhancement are 

 best sought for by the use of such material; often it will also be 



