Cross immunological reactions between three haptens of the "para" group and 4-aminoantipyrine.

Cross passive hemagglutination reactions between sulfanilic acid (SA), para-aminobenzoic acid (PABA), p-phenethidine (PT) and 4-aminoantipyrine (4-AA) haptens have been investigated using conjugates of diazo derivaties of these compounds with homologous serum proteins. Intense cross passive hemagglutination reactions were found between PABA, SA and 4-AA haptens. Although anti-PT sera cross reacted intensely with PABA, SA as well as with 4-AA haptens, antibodies cross reacting with PT were not detected in any of the anti-PABA, anti-SA and anti-4-AA antisera. The conjugates containing a heterologous hapten de not substantially alter the titer of the hemagglutination reactions performed with erythrocytes coated with the homologous hapten, but completely suppress the hemagglutination reactions performed with erythrocytes coated with this hapten as well as with other, but not all, heterologous, haptens. The results support the conclusion that the apparent polysensitization to drugs may actually rely upon cross reactions with haptens chemically related to the immunizing one.