In vitro stimulation of spleen cells of the mouse by DNP--carrier complexes.

Hapten—carrier complexes were prepared with the 2,4-dinitrophenyl group (DNP) as a hapten and bovine serum albumin (BSA), bovine gamma-globulin (BGG) (heterologous), mouse immunoglobulin (MIg) (isologous) and polyvinyl pyrrolidone (PVP) (thymus-independent) as carriers. All complexes could be used for priming, independent of the type of carrier or the number of DNP groups. No response, however, could be obtained with any of the DNP—PVP complexes or with the complexes with a low hapten/carrier ratio (about 3). Priming with carriers alone resulted in some activity on challenge with the homologous DNP—carrier complexes, but this response was less than after priming with one of the homologous DNP—carrier complexes. Cross-reactions between DNP—MIg, DNP—BGG and DNP—BSA complexes could be obtained. In almost all instances challenge with BSA with the highest number of DNP groups (DNP—BSA) resulted in the highest activity. Inhibition of the reaction could to a certain extent be obtained with ε-DNP—L-lysine. These experiments suggest that: (1) for priming, the hapten/carrier ratio is of no importance and the influence of the type of carrier is low; (2) stimulation can only be obtained with complexes with a high hapten—carrier ratio; when this ratio approaches a maximum (DNP—BSA) the type of the carrier used by priming seems to be irrelevant; (3) the data from these experiments, from cross-reactions and from inhibition reactions suggest that the stimulating activity of DNP—BSA is due to the DNP groups, but the activity of complexes such as DNP—BSA, DNP—BGG and DNP—MIg is at least partly due to the `new antigenic determinant' (NAD) or DNP—NAD groups.