Mechanism of Intensification by Complete Freund's Adjuvant of the Acquisition of Delayed Hypersensitivity in the Guinea Pig

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Abstract
In the guinea pig, delayed administration of complete Freund's adjuvant (CFA) to skin sites previously primed with a cellular antigen leads to a marked intensification of the acquired sensitivity to that antigen. This effect has been demonstrated with diverse cellular antigens including foreign erythrocytes (both fresh and formaldehyde treated), HeLa cells and dead bacteria, Thus, when a borderline-sensitizing quantity of cells is given intradermally on Day 0, followed by adjuvant into the same site on Day 4, there results a marked intensification of the delayed hypersensitivity reaction to Day 6 testing with the priming cells in the adjuvant treated animals. It appears that CFA intensified acquisition of delayed hypersensitivity to cellular antigens, as well as to soluble protein antigens and contact allergens, involves two steps: 1) initial interaction of antigen with immunocompetent cell, 2) subsequent stimulation by adjuvant of immunocommitted cells (probably by enhancing their clonalization). It appears that the CFA effect takes place primarily in lymph nodes regional to the sensitization site.