Abstract: | An extremely thermostable and resistant to some chemical substances factor was found in the sera of Wistar and noninbred rats of different age, male and female. This factor inhibited the action of normal and immune antibodies to rat erythrocytes and rat serum antigens. The blocking factor was relatively specific and more effective in respect to the normal antibodies than to the immune ones. The activity of the blocking factor was connected with the alpha1-globulin. |