Immunoglobulins in Hassall's corpuscles of the human thymus

Ninety nine human thymuses were examined immunohistochemically for the presence of immunoglobulins G, A, M. D and E, light-chains, secretory component and albumin in the cells of Hassall's corpuscles. Igs G, A, M and secretory component were present. These showed a rise after birth until the age of 20 years and also increased with the degree of involution, falling when involution became complete. Albumin was also consistently demonstrated. There was a degree of correlation between the presence of Igs and production of Igs G, A and M by plasma cells in the thymic medulla. There was a close correlation between the amounts of IgA and secretory component in the cells of Hassall's corpuscles and the thymus may have to be regarded as a part of the secretory-IgA system. Light chains of the immunoglobulin molecule were also present, with lambda predominating over kappa, possibly reflecting the same kappa/lambda ratio found with thymic immunoglobulin production. No IgD or IgE was demonstrated. The presence of albumin may represent a passive uptake of protein in senescent cells but a more active uptake of Igs, particularly IgG and IgA, could be postulated. The production of Igs in the thymus and their presence in Hassall's corpuscles could be of significance in the maturation and regulation of the immune response.