The interaction of tetanus toxin and antitoxin

Tetanus antitoxic horse sera were fractionated with sodium sulphate and by electrophoretic separation. The activity of the native serum and of fractions was determinedin vivoin the mouse and guinea-pig andin vitroby the flocculation method. All the sera and fractions showed several zones of flocculation. The flocculation optimum corresponding to the toxin-antitoxin complex was selected by absorption of antitoxin to the floccules. The distribution of activity amongst the electrophoretic components of the native serum was computed from electrophoretic analysis, refractive increment measurements and assays of the activity of the electrophoretically pure fractions. In all the sera examined the antitoxin was associated with both β- and γ-globulin. The γ-globulin antitoxin had a shorter flocculation time and a higherin vivo/in vitroratio than β-globulin. Thein vivo/in vitroratio of γ-globulin was two to three times that of β-globulin antitoxin, its exact value depending on the toxin concentration against which the antitoxin was measured. The avidity of γ-globulin antitoxin was greater than that of β-globulin antitoxin judged by two independent ‘dilution’ tests, namely a comparison of the mouse unitage using two concentrations of toxin and a comparison of the values obtained with one concentration of toxin in the mouse and in the guinea-pig. Thein vivovalues of the various antitoxins varied with the toxin employed in the test. During the first course of immunization in a horse the γ-globulin antitoxin rose to a constant value; β-globulin antitoxin increased to a still higher value later in the course. The avidity of the serum, as measured by the two ‘dilution’ ratios, also increased during immunization.