The incidence of thymic B lymphoid follicles in healthy beagle dogs

The incidence of thymic B cell lymphoid follicles was retrospectively studied in 62 male and 58 female healthy control beagle dogs (age 11.3 +/- 4.8, range 6 to 23 months). The animals were selected from toxicological studies performed in the period 1990-2001 at the Organon labs. The animals had received vehicle treatment. Thorough microscopic examination of the thymus in hematoxylin & eosin (H&E)-stained sections resulted in an unexpectedly high overall incidence of 70% of medullary lymphoid follicles. Occasionally, these lymphoid follicles contained germinal centers. With the use of a T- and B cell marker (respectively CD3 and CD79alpha) we confirmed that the lymphoid follicles exclusively contained large numbers of B lymphocytes. Moreover, with the use of the B cell marker, almost all animals (97%) prove to have B cell rich medullary areas. The study also confirmed that the dog thymus underwent progressive involution during the period from 6 to 23 months of age. As a consequence of the involution, B cell areas and lymphoid follicles may be obscured in some H&E sections. Results of this study indicated that dense B lymphocyte aggregates and/or B lymphoid follicles are a normal constituent of the canine thymus.

Fc gamma receptors and HLA-DR antigens on thymus cells in myasthenia gravis

Receptors for the Fc part of IgG (Fc gamma R) and HLA-DR antigens were detected in thymus tissue from patients with myasthenia gravis (MG) using monoclonal antibodies (B1D6 and OKIa1) in indirect immunofluorescence. The amount of Fc gamma R and HLA-DR antigens was increased on epithelial reticular cells and on interdigitating reticular cells in hyperplastic thymus as compared to normal thymus. In thymomas from MG patients the neoplastic epithelial cells expressed Fc gamma R, whereas only a few cells had HLA-DR antigens. Neither thymocytes nor B lymphocytes in the hyperplastic thymuses and in the thymomas were stained by B1D6.

Rabbit antiserum to a citric acid extract of human skeletal muscle staining thymomas from myasthenia gravis patients

Rabbit antiserum to a citric acid extract of human skeletal muscle (CA) stained both the cell membrane and the cross-striational bands of skeletal muscle cells. The rabbit antiserum also stained the cell membrane of epithelial thymoma cells from myasthenia gravis (MG) patients. Normal and hyperplastic thymus tissue were not stained, apart from scattered myoid thymic cells. Absorption of the antiserum with CA abolished staining of the thymoma, indicating that human skeletal muscle and epithelial thymoma cells possess common antigens.

Leu 7+ (HNK-1+) cells. I. Selective compartmentalization of Leu 7+ cells with different immunophenotypes in lymphatic tissues and blood

In the present immunohistochemical studies, Leu 7+ (HNK-1+, human natural killer and killer) cells were found to occupy preferentially germinal centres of follicles in lymph nodes and tonsils. Leu 7+ cells were also present in germinal-like zones of spleen follicles and in mantle zones of hyperplastic thymus follicles and varied in localization in lymph nodes involved in different types of follicular centre cell-derived malignant lymphomas. Most of the Leu 7+ cells in the follicles expressed the Leu 3 (helper/inducer) marker. Double staining studies of tonsil sheep erythrocyte-rosetting and peripheral blood mononuclear cell suspensions showed that two main, mutually complementary, subpopulations of Leu 7+ cells could be distinguished in both cases, namely Leu 7+/Leu 4+ (subdivided into Leu 2+ (suppressor/cytotoxic) and Leu 3+) and Leu 7+/Leu 4-, including mostly cells with OKM 1 (myelomonocytic) characteristics. Thus, in the tonsil cell suspension the cells with Leu 7+ Leu 3+/OKM 1- immunophenotype strongly predominated, whereas among peripheral blood mononuclear cells Leu 7+Leu 2+/OKM 1- and Leu 7+/OKM 1+ immunophenotypes were mostly observed.

The ontogeny of immunological receptors in the thymus

Receptors for sheep erythrocytes, for the Fc part of IgG (Fc gamma R) and IgM (Fc mu R), and for components of activated human complement C3 (C3bR and C3dR) in thymus tissue from fetuses, infants and children were studied using haemadsorption to cryostat sections in a closed chamber. Sheep erythrocytes (SE) did not adhere to sections of thymus from fetuses at 10-11 weeks of gestation, adhered weakly between 14 and 20 weeks, while they adhered in a dense monolayer in older fetuses, in infants and in children, denser in the cortex than in the medulla. Ox erythrocytes (OE), sensitized with IgG to demonstrate Fc gamma R, adhered focally to both cortical and medullary areas. The adherence was more pronounced to the sections of fetal thymus than to the sections from infants and children. OE, sensitized with IgM to demonstrate Fc mu R, adhered focally to all thymus tissue sections, preferentially to the cortex. The adherence was most pronounced in fetal thymus. SE, sensitized with IgM and coated with complement, adhered to sections of fetal thymus, but the density decreased markedly during fetal life. Indicator cells demonstrating C3bR adhered focally also to sections from infants and children, while indicator cells demonstrating C3dR did not adhere to sections from individuals older than 38 weeks of gestation. Indicator cells demonstrating C3bR and C3dR adhered both to cortex and medulla.

Acetylcholine receptor turnover in myasthenia gravis

Humoral antibodies directed against the acetylcholine receptor are present in most patients with myasthenia gravis. These antibodies accelerate receptor degradation and thus cause a decrease in receptor level and impaired neuromuscular transmission. The stimulus that triggers and sustains the formation of the antibodies has not been identified, but it is possible that the primary antigen may be located on the cell surface of thymic lymphocytes. In some situations the clinical state in myasthenia gravis does not correlate with the antibody titer, suggesting that other factors also influence receptor amount and/or function of other potential regulators that have been investigated. Calcium and agents that increase cyclic AMP appear to increase the formation of the receptor and thus might serve to mitigate the effects of the circulating antibodies. In contrast, cholinergic agonists may cause a further decrease in receptor number, providing an explanation of why myasthenic patients may become resistant to therapy.