Basement membrane proteins and reticulin in a normal thymus and the thymus in myasthenia gravis.

The distribution of basement membrane (BM) proteins, laminin and type IV collagen were studied immunohistochemically in a series of 12 normal thymuses representing different age groups (0-52 years) and in 10 cases of myasthenia gravis (age 7-53 years). The staining pattern was compared with that of conventional reticulin staining. BM proteins were present at the capsule-parenchyma interface and scantily distributed in the medullary stroma, where they were closely associated with reticulin fibres. The extrathymic perivascular space was effectively visualized by the staining of the BM's marginal to it. The fiber network present in this space stained with reticulin stain and, less continuously, in BM stainings. Lymph node like tissue with germinal centers was occasionally present in the perivascular spaces in normal thymuses and commonly in the myasthenia gravis cases, where the perivascular spaces were often dilated. The BM's of the perivascular space were mostly continuous in normal cases, but discontinuities were observed in cases of myasthenia gravis, especially in the spaces which were widely dilated. Immunohistochemical detection of BM proteins seems to be useful in the study of thymic structure, particularly in the demonstration of the characteristic changes of the perivascular space in myasthenia gravis. It is suggested that the reticulin fibres present in the medulla and in the perivascular space contain laminin and type IV collagen.