Delayed-type hypersensitivity in rabbits. Comparison of the adjuvants dimethyl dioctadecyl ammonium bromide and Freund's complete adjuvant.

Injection of rabbits with antigen mixed with the cationic surface-active lipid dimethyl dioctadecyl ammonium bromide (DDA) induced delayed-type hypersensitivity (DH), which could be measured as skin reactions and was confirmed by histology of the skin test sites. 1 week after injection of a conjugate of bovine serum albumine (BSA) with dinitrophenol (DNP30-BSAj) mixed with DDA, DH was detectable in most but not in all rabbits. Similar results were obtained using FCA as adjuvant. The animals treated with the latter adjuvant, however, produced a long-lasting DH (1-3 weeks) complicated by circulating anti-DNP antibodies (Arthus-type reactions). Skin testing with heterologous hapten-carrier complexes revealed that individual rabbits immunized with DNP30-BSA in DDA expressed DH with different reaction patterns, either to hapten, carrier or both. In conclusion, DDA is a useful adjuvant for the induction of a state of pure DH in rabbits. However, not all rabbits do respond, or respond similarly.