Immunodetection of the thymic epithelial P19 antigen in cultures of normal and pathological human thymic epithelium.

We investigated by an immunofluorescence assay the presence of the P19 antigen in cultures of human thymic epithelial cells (HTEC). This antigen is acquired during human thymic ontogeny, and in infants and adults most thymic epithelial cells were shown to display P19 antigen. In cultures of normal human thymic epithelium, we observed that the P19 protein was less expressed than in situ. However, the percentage of P19-containing cells increased with culture age, a finding which could be compared to that obtained recently concerning immunodetection of thymulin-containing cells. Indeed, thymic epithelial cells keep their endocrine function in culture and the number of thymulin-positive cells increases as a function of time. Interestingly, the increase of P19 expression was generally parallel to that of thymulin production. These data may reflect functional modifications of the cells in relation to differentiative effects. Similar results were obtained in pathological thymuses described as hyperplasia in M G patients. In contrast, thymomas behaved differently. Among the three benign thymomas tested, two were consistently P19-negative or faintly stained in culture conditions while one was very brightly stained from the onset and remained P19-positive throughout the culture; this finding correlates with studies on frozen sections. Our data show modifications of P19 antigen expression both in culture and in thymomas and suggest that P19 synthesis may be dependent upon components (factors or cells) which are efficient in the thymic microenvironment but partially defective in the cultures or after neoplastic transformation.