Fundamental study on the structure and functions of lymphoid follicles with germinal center observed in the thymuses of patients with myasthenia gravis

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The developing lymphoid follicles in the thymuses of patients with myasthenia gravis (MG) were immunohistochemically investigated with emphasis on the structure and functions of the thymus.The follicles were composed of abundant immature B lymphocytes and some elongated epithelial cells in which tonofilaments and desmosomes in the cytoplasm were confirmed by an immunoelectron microscopic method. These epithelial cells as well as B lymphocytes reacted with L26ab. They were not present in the follicles of the lymphnodes. Although a significant population of B lymphocytes was confirmed in the follicle, only a few immunoglobulin-bearing cells were present in the thymuses together with the follicles at about 30 % patients and lacked in the remaining thymuses, furthermore, no rearrangement of immunoglobulin heavy chain gene (Igh) was recognized in these thymic tissues. The epithelial cells in the thymic follicles were structurally similar to those in the medullary zone of the human neonatal … More thymus.Regarding apoptosis of the thynic tissues from MG patients, expression of Fas antigen related to apoptosis was reduced in the lymphoid follicles of the thymus, but was diffusely significant in the remaining thymic tissues. BMI antigen was not expressed in the lymphoid follicles nor other parts of the thymus. Fas mRNA was also decreased to a varying degree in the thymic tissues.Thymomas of patients with MG were at about 45 % associated with medullary differentiation or lymphoid follicles that were not found in thymomas of patients without MG.B lymphocytes were concentrated in these areas, but immunolobulin-bearing cells were scarce or lacked.From these results, it was concluded that B lymphocytes concentrated in the follicles of the thymuses or thymomas from patients with MG revealed a state of preactivated antibody production, the epithelial cells in the lymphoid follicle of the thymus might be related to an immunological function associated with antibody production and the cells included in the lymphoid follicles might be able to reduce a negative regulation for T lymphocytes in the thymuses of patients with MG. Less