Immunological studies on human thymus. Occurrence and distribution of immunoglobulins and immunological receptors in myasthenia gravis and control patients.

Suspended cells and tissue sections from myasthenia gravis (MG) and control thymuses were characterized for surface expression and histological distribution of immunoglobulin (Ig) and receptors for sheep erythrocytes (SE), the Fc part of IgG (Fc gamma) and of IgM (Fc mu) and complement factors C3b and C3d (CR). In sections the cortical areas from both MG and control thymuses expressed SE as well as Fc gamma receptors, whereas medullary areas only showed weak SE binding. In contrast to control patients, MG thymuses also contained Ig+ cells confined to nodular areas of the thymic medulla. These nodules stained for both IgG and IgM, and were polyclonal with respect to light chains. In several cases IgD was found as well. In addition, the nodular areas were positive for C3b and C3d receptors. In serial sections, these Ig+ CR+ nodules corresponded to morphologically characteristic lymphoid follicles. Such B cell follicles were observed in variable numbers in all MG thymuses, whether hyperplastic or with normal histology. Five thymomas gave heterogeneous results with regard to immunological markers. Comparison of methods showed that receptor and Ig indication on sections was more sensitive than corresponding tests on thymus cells in suspension.