Haemagglutination-inhibition studies of the combining sites of anti-peptide antibodies in mice and rats.

Antibodies of poly-D-alanyl specificity were produced in goats, rabbits, rats and mice by immunization with poly-D-alanyl ribonuclease. The reaction of the sera with formalinized sheep erythrocytes, tanned and coated with poly-D-alanyl human serum albumin, was inhibited with oligopeptides of D-alanine of increasing size. The upper limit of the size of goat and rabbit antibody combining sites was complementary to a tetrapeptide, in agreement with results obtained by inhibition of precipitin reaction. Since the data obtained with both methods compared favourably, the upper limit size of mouse and rat antibody combining sites of poly-D-alanyl specificity was estimated by the passive haemagglutination-inhibition technique. The results suggest that such sites are similar in size to those of rabbit and goat antibodies, and are capable of accommodating a peptide composed of four alanine residues.