Agglutinins to rabbit erythrocytes in extracts of human malignant tissues

Agglutinins to rabbit erythrocytes in extracts from human malignant tissues were identified as the naturally occurring IgG antibodies in human serum to rabbit erythrocytes. This was revealed by agglutination, absorption, antiglobulin and inhibition tests, immunization of rabbits and immunochemical analyses. The agglutinins can therefore be used as convenient markers for both extracellular immunoglobulin and unspecifically bound immunoglobulin in tumour tissues. Apparently the extracts also contained small amounts of IgA antibodies to rabbit erythrocytes.