THE CYTOPLASMIC AUTO-ANTIGEN OF THE HUMAN THYROID. I. IMMUNOLOGICAL AND BIOCHEMICAL CHARACTERISTICS.

The reaction between the thyroid microsomal antigen and Hashimoto sera was studied by quantitative complement-fixation. Iso-fixation curves indicated a heterogeneity among individual sera and cross-absorption experiments suggested that this could be attributed to antibodies with differing abilities to fix complement with the same antigenic determinants. The results of equilibrium density gradient centrifugation, electron microscopic and immunofluorescent studies were consistent with an association of the antigen with small smooth-surfaced vesicles in the microsomal fractions. The effect of enzymes, detergents, organic solvents and other chemical and physical treatments suggests that the complement-fixing antigen is an insoluble lipoprotein intimately bound to the structural elements of the vesicle membranes. Organ-specific antibodies were obtained on immunization of a rabbit with human thyroid microsomes. The microsomal antigen may provide a model for organ-specific components in other tissues able to provoke or sustain auto-immune diseases.