Biological studies with an iodine-containing synthetic immunological determinant 4-hydroxy-3-iodo-5-nitrophenylacetic acid (NIP) and related compounds

Immunization with 4-hydroxy-3-iodo-5-nitrophenylacetic acid (NIP)—protein conjugates, and assay of antisera by binding of N¹³¹IP—ε-amino-n-caproic acid (N¹³¹IP—aminocap), is used to investigate the response of CBA mice. Primary immunization is obtained more efficiently with alum-precipitated conjugates mixed with pertussis, than with conjugates alone or in Freund's complete adjuvant, and is most efficient with conjugates of chicken serum globulin (NIP—CG) or edestin. The mice invariably respond to efficient immunization. Secondary responses have been obtained by stimulation in vitro or in vivo of spleen cells transferred from primed donors. Cells taken from donors primed with NIP—ovalbumin respond detectably to as little as ~0.001 μg NIP—ovalbumin/mouse, but are less sensitive to stimulation with NIP—bovine serum albumin (NIP—BSA). Secondary stimulation by NIP-conjugate is subject to competitive inhibition by NIP—aminocap. Prolonged administration of NIP—BSA or NIP—BGG renders mice partially unresponsive to immunization with NIP—CG, but the degree of immunological paralysis obtained is less than that obtained towards the carrier protein.