SESSILE AND HUMORAL ANTIBODIES 229 



immunization by the intradermal route, use of small antigen dose 

 particularly as antigen-antibody complexes (Uhr, Salvin and 

 Pappenheimer, 1957), sublethal irradiation (Salvin and Smith, 

 1959) — all prolong the delayed hypersensitive state which tends 

 to disappear as humoral antibody synthesis accelerates. Such an 

 explanation might also account for the examples of prolonged 

 graft survival when immunization by the intravenous route with 

 non-paralysing antigen doses has been used (Billingham and 

 Sparrow, 1955; Prehn, 1959). Leskowitz and Waksman (i960) 

 have shown that immunization by this route in rabbits is known to 

 provoke a good humoral response, but a low level of delayed 

 hypersensitivity which is further depressed by a booster intra- 

 venous dose. In guinea pigs delayed reactions to chemicals such as 

 2 : 4-dinitrochlorobenzene are rarely achieved when subcutaneous 

 and intravenous immunization is performed (Landsteiner and 

 Jacobs, 1936). The inhibition of experimental allergic encephalo- 

 myelitis in rabbits, rats, and guinea pigs by prior treatment 

 with nervous tissue unmixed with adjuvants increases with re- 

 peated immunization. In a discussion upon this subject Waksman 

 (1959) mentions the possibility that the various forms of delayed 

 hypersensitivity may be diminished by a "vigorous conditioning 

 of the immune apparatus to another type of response", namely 

 a humoral one. 



The adoptive enhancing activity described has been previously 

 observed by Mitchison and Dube (1955). Presumably the incon- 

 sistent results obtained in the BALB/c hosts are related to the fme 

 balance existing between the cells secreting humoral antibody, and 

 those in a state of hypersensitivity. The influence of splenectomy 

 has been examined by previous workers (for references see 

 Woglom, 1929) some of whom, as in this paper, record increased 

 resistance. If this represents the prevention of a degree of auto- 

 enhancement, it is to be expected that not all tumour-host 

 combinations will allow the observation of this effect, particularly 

 those tumours of extreme sensitivity to isoantisera. 



