Depression of delayed hypersensitivity by pretreatment with Freund-type adjuvants. I. Description of the phenomenon.
Delayed hypersensitivity induced by antigen in Freund's complete adjuvant (FCA) can be depressed by pretreatment with FCA alone beforehand. In the guinea-pig, pretreatment with FCA depressed the 24 hr skin reactions which otherwise followed immunization with bovine γ-globulin, human serum albumin and the arsanil-N-acetyl tyrosine in FCA. The depression ranged from 25 to 75% and 4 hr skin reactions were also depressed. In contrast, haemolytic and cytophilic antibody to BGG was not depressed by pretreatment with FCA before immunization with antigen in FCA. 
 
It was not necessary to use the same adjuvant for pretreatment and immunization, and pretreatment with FCA or Corynebacterium parvum adjuvant depressed delayed hypersensitivity to BGG induced by BGG in either FCA or C. parvum adjuvant. 
 
In both the guinea-pig and rat, pretreatment with FCA, and soluble antigen acted synergically in depressing 24 hr delayed skin reactions. Thus pretreatment with either FCA or soluble antigen, before immunization with antigen in FCA depressed delayed hypersensitivity skin reactions, and pretreatment with both agents caused a greater depression than either singly. However pretreatment with FCA did not alter the depression of antibody production caused by soluble antigen. 
 
In the mouse, pretreatment with FCA or C. parvum depressed contact sensitivity to picryl chloride induced by picryl chloride in FCA. Contact sensitivity to picryl chloride and oxazolone induced by skin painting was not depressed by pretreatment with FCA.