An unusual inhibition of an anti-P1.

Tests for unexpected antibodies using commercially prepared red blood cells demonstrated no agglutination even though crossmatching and testing with saline washed commercially prepared reagent red blood cells identified an anti-P1. This antibody was inhibited when tested with red blood cells suspended in a modified Alsever's solution and several commercially prepared reagent red blood cell diluents. The inhibitory substance was identified as inosine. Hypoxanthine, adenine, and thymine also inhibited the anti-P1. Partial inhibition was produced by uracil, 5-methylcytosine, and xanthine. No other example of anti-P1 has been found to exhibit this unusual inhibiting characteristic.