An antibody to human thymic Hassall's body epithelium recognizes a subset of blood group A antigens

[Target epitopes of monoclonal antibodies against ABH structures]

Comparing the reactivities of murine and human monoclonal antibodies directed against the antigens of A, B, and H blood groups by using different techniques (agglutination, inhibition by synthetic oligosaccharides and salivary antigens, tissue immunofluorescence, the use of an anti-idiotype antibody) enabled us to show a high heterogeneity of anti-A, anti-AB antibodies and, to some extend, anti-B and anti-H antibodies. Despite this diversity, the determination of the antibody specificity thanks to synthetic antigens made it possible to distinguish several groups of anti-A, B, AB, and H antibodies and to establish a classification that takes also their reactivity towards salivary and tissue antigens into account. On the contrary, few correlations were found between these tests and the ability of antibodies to agglutinate red blood cells of the different ABO-system variants.

Expression of ABH, Lewis and related tissue antigens in the human thymus

Expression of ABH, Lewis and related antigens was studied in the thymus of children of known ABO, Lewis and secretor status using a panel of specific reagents. ABH and Lewis antigens partly under control of the secretor status were expressed on the Hassals' bodies and a large fraction of the medullary epithelial cells. The sialyl-Lea antigen was only present on some Hassals' bodies of Lewis-positive individuals. ABH but not Lewis antigens were also present on cortical epithelial cells but this was independent of the secretor status. The X, sialyl-X and Y antigens were only expressed on Hassals' bodies irrespective of the ABO, Lewis or secretor phenotype. Furthermore, the anti-X and sialyl-X antibodies labelled a subset of leucocytes of all the individuals tested. These results show that the genetic control of the expression of ABH and Lewis glycosidic tissue alloantigens in the thymus is different on cortical and medullary epithelial cells and stress the heterogeneity of the thymus epithelial cells.

Thymic medullary cells expressing B lymphocyte antigens

A small subpopulation of human thymic medullary cells was found to express B cell-restricted and -associated antigens in various combinations. The cells were detected in fetal, juvenile, and adult thymi using indirect immunoenzymatic methods and monoclonal antibodies (MoAbs). Morphologically, they could be subdivided into small, round lymphoid cells, accounting for less than 1% of medullary lymphoid cells, and into a larger variant, even more infrequent in number and asteroid in shape because of short cytoplasmic processes. Immunophenotype (CD19+, CD20+, CD22+, CD37+, IgM+, IgD+) and morphology of the first cell type led to the conclusion that the lymphoid cells were B lymphocytes. The second, asteroid cell type constantly expressed CD20 and inconstantly expressed IgM, CD19, CD22, and CD37; they were often found to form rosettes with non-B lymphocytes. It can be concluded that a small number of B cells and asteroid cells of still uncertain origin, but expressing B cell-restricted antigens, are constitutive elements of the fetal and adult thymic medulla. It can be hypothesized that the asteroid cell might represent a novel type of thymic accessory cell and that the rosetting of non-B lymphocytes around this asteroid cell might simulate or in fact be the earliest B cell interaction of maturing T cells.

Intra- and extrathymic B cells in physiologic and pathologic conditions. Immunohistochemical study on normal thymus and lymphofollicular hyperplasia of the thymus

Normal thymuses and thymuses with lymphofollicular hyperplasia have been examined immunohistologically using immunoenzymatic single and double labelling methods and a panel of monoclonal antibodies against B lymphocyte differentiation antigens (CD19-, CD20-, CD21-, CD22-, CD23- and CD37ag) and human immunoglobulins (IgM, IgD) for the presence and localisation of B lymphocytes and cells expressing B cell differentiation antigens. The numerous hyperplastic lymph follicles which occur in the pathological condition of lymphofollicular hyperplasia of the thymus were found to originate in the extrathymic compartment of the interlobular septal space. This area was found to be blown up by the growing lymph follicles with exactly the same cellular composition as their counterparts in the peripheral lymphatic tissue. Some of the B lymphocytes expressing the immunophenotype of follicular mantle zone lymphocytes which were detected in the thymic medulla probably infiltrated through discontinuities of the border between the perivascular space and the thymic medulla. Apart from this primarily extrathymic B cell compartment, B lymphocytes and cells expressing B cell antigens were found within the thymus medulla of normal control thymuses of different ages from fetal to adult life. These cells were detected as a small subpopulation in normal fetal, juvenile and adult thymuses. Morphologically they could be subdivided into small, round lymphoid cells accounting for less than 1% of medullary lymphoid cells, and into a larger variant, asteroidally shaped because of short cytoplasmic processes. These asteroid cells were even more infrequent than the lymphoid variant. Immunophenotype (CD19ag+, CD20ag+, CD22ag+, CD37ag+, IgM+, IgD+) and morphology of the first cell type led to the conclusion that the lymphoid cells were in fact B lymphocytes. They were scattered throughout the medulla of fetal and juvenile and adult thymuses alike. The second, the asteroid cell type, constantly expressed CD20ag and inconstantly IgM, CD22ag and CD37ag; furthermore, CD23ag was detected in a subset of the asteroid cells either restricted to the perinuclear zone or expressed in the entire cytoplasma and on the plasma membrane. The asteroid cells were located in the corticomedullary region of the fetal thymuses but were randomly distributed with a tendency to Hassall's corpuscles in juvenile and adult thymuses. They often formed rosettes with non-B lymphocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Human erythrocyte antigens. III. Characterization of a panel of murine monoclonal antibodies that react with human erythrocyte and erythroid precursor membranes

Human erythrocyte membrane proteins express antigens which serve as markers for erythroid differentiation as well as targets for human blood group alloantibodies. We have produced and characterized a new panel of five monoclonal antibodies to erythrocyte membrane proteins. Three monoclonal antibodies (E3, E4, E5) were specific for erythrocyte glycophorins. One antibody (E3) identified the sialoglycoprotein alpha and beta homologous regions proximal to the plasma membrane, a second antibody (E4) was specific for sialoglycoprotein alpha, while a third (E5) was a sialoglycoprotein-beta-specific antibody. Two antibodies (E6 and TE10) to the 65,000-dalton chymotrypsin cleavage product of band 3 were also produced. These antibodies constitute a new panel of probes for investigation of normal erythroid differentiation, erythroleukemia, and the expression of normal and anomalous blood group antigens.

The thymic microenvironment. Characterization of in vitro differentiation of the IT26R21 rat thymic epithelial cell line

We have previously postulated an in vivo pathway of thymic epithelial (TE) cell maturation in pre- and postnatal thymus, whereby endocrine medullary TE cells terminally differentiate to form Hassall's bodies. Epithelial-cell differentiation has been well documented in vitro using epidermal keratinocytes. Therefore, to characterize TE-cell differentiation in vitro, we observed clones of the rat TE cell line, IT26R21, after 4 and 14 days in culture. We found alterations in cell morphology, the cessation of cell proliferation, and the acquisition of a differentiation antigen defined by monoclonal antibody TE-19 (a marker of terminally differentiated epithelial cells). At light and electron microscopy, we detected progressive TE-cell stratification and squamous-cell formation between 4 and 14 days of culture. Autoradiography on day 14 showed that squamous TE cells in stratified layers did not incorporate tritiated thymidine, while surrounding smaller cells adhering to the substratum continued to synthesize DNA. At indirect immunofluorescence, only 3% of cells reacted with monoclonal antibody TE-19 at day 4, while on day 14, 22% of the TE cells were TE-19 positive (P less than 0.02). Antibody-TE-19 reactivity was limited to stratified, squamous TE cells. Additionally, we isolated a clone of the IT26R21 cell line that did not undergo these changes characteristic of TE cell differentiation. We conclude that IT26R21 TE cells are capable of undergoing programs of both terminal differentiation and cell renewal in vitro.