Use of Lightly Haptenated Phage to Detect High-Affinity Antibody.

We coupled bacteriophage T4 with standard (0.16%) or low (0.005%) concentrations of NIP-azide. The low concentration produced haptenated phage (type B) that was inactivated by the IgG anti-NIP of some rabbits but not by that of other rabbits similarly immunized. The most active IgG fraction at an anti-NIP concentration of 100 µg/ml inactivated the type B phage with a titre of 2400, while the same anti-NIP concentration of the least active IgG fraction from another rabbit had a titre of 0.3. With the standard haptenated phage titres only varied within a 20-fold range. IgM fractions of a few rabbits tested did not appear to exhibit a great variation with the type B phage. The IgG fractions with high titres against the type B phage bound more NIP-hapten at low (≈ 10^-10M) hapten concentrations than those with a low titre, but this superiority was greatly reduced by an increase of hapten concentration to 10^-8M. The same phenomenon could be demonstrated by an inhibition technique, lnactivation of type B phage appeared to detect exclusively antibodies with association constants considerably higher than 10⁸. Its affinity threshold seems to be higher than the threshold of two other methods employed, haemagglutination of haptenated erythrocytes and inactivation of the standard haptenated phage. [ABSTRACT FROM AUTHOR]