Functional relationship of macrophages and basophils to the thymus gland

Transplantation of cultured thymic fragments: results in nude mice. V. Reconstitution with xenogeneic (rat) thymic tissue

Transplantation of F344 rat cultured thymic fragments was able to restore immune function to nude mice. Approximately half of such animals displayed increased lifespan (7-8 months). These mice were also capable of rejecting allogeneic mouse skin and rat skin from a strain (Buffalo) unrelated to the thymus donor; however, they were incapable of rejecting rat skin from the thymus donor strain. Proliferative responses to T-cell mitogens were restored. Proliferative responses to alloantigens and xenoantigens in mixed leucocyte cultures were also restored and showed the same patterns of specific reactivity and non-reactivity as in skin graft rejection. The ability to make antibody responses to specific antigens was also restored, but the responsiveness was more variable than for cell-mediated responses. Some mice were able to make antibody to rabbit serum proteins; however, fewer mice made antibody to ovalbumin. The inability to respond to ovalbumin may be due to the fact that F344 rats are low responders to this protein. These results suggest that cultured xenogeneic thymus is effective in restoring two major differentiation functions of the normal thymus gland: development of specific antigen responsiveness and non-responsiveness.

Studies on the in vitro culture of murine fetal thymus: effect of factors promoting epithelial growth

Fourteen-day fetal thymus was grown in organ culture under conditions reportedly optimizing epidermal/epithelial cell growth. While the fibroblastoid component is stimulated by epidermal growth factor and fibroblastoid growth factor, embryonic thymic epithelial cells do not grow significantly under any conditions, although they persist in organ explants. The major cell types cultured are fibroblastoid and macrophage. In organ explant cultures, epithelial cells appear to be oriented by the presence of a cell coat demonstrated by electron microscopy. This coat is absent from certain ciliated cells consistently found in deeper regions of the explant. Using amniotic fluid as a growth factor, almost pure cultures of thymic macrophages can be obtained.

Thymic microenvironment and cultures derived from mouse thymic explants. A morphological study

Cultures derived from thymus fragments of embryonic (18-19 day old), newborn or one month old C57BL mice have been characterized functionally l(phagocytic and nonspecific esterase activities) and morphologically by means of light, scanning (SEM) and transmission (TEM) electron microscopy. The observations show the heterogeneity of the cell populations composing the monolayers. After a few days incubation macrophages appear as the predominating cell type, while epithelial cells usually constitute no more than 30% of the cells. Experiments designed to determine the fate of lymphocytes adhering to the monolayers lead us to believe (on the basis of SEM morphometric analysis) that the survival of lymphocytes attached either to thymic macrophages or to epithelial cells is improved during the first days of coculture. This survival enhancement does not, however, appear to be a specific inductive effect since a similar survival increase is found when lymphocytes adhere to non-thymic cells. In contrast with the monolayer, the explant provides a three-dimensional culture system able to preserve intact thymic microenvironmental conditions since numerous lymphocytes are found even in five week old cultures which were not overlaid with thymocytes or spleen cells.

Basophil production

Factors influencing basophil production from the bone marrow of ovalbumin (OA)-sensitized guinea pigs have been examined in vitro. Autologous co-cultures of marrow and spleen cells from OA-immune animals contained significantly higher numbers of basophils after 7 d of liquid culture in the presence of OA, compared with control co-cultures or with marrow cultures alone (P < 0.005). Basophils increased in co-culture as the number of spleen cells added to a fixed number of marrow cells was increased from 0.10 to 2.5 x 10(6)/ml; at each spleen cell concentration, the presence of OA significantly enhanced basophil production in vitro when compared with unstimulated co-cultures. There was no basophil production from spleen cell suspensions cultured in the absence of autologous marrow cells. Conditioned media (CM) prepared from OA-stimulated spleen cells of OA-treated animals (CM-OA) caused a specific stimulation of basophil production from normal guinea pig bone marrow cells in liquid cultures (P < 0.01). Phytohemagglutinin (PHA)- and pokeweed mitogen-stimulated CM (CM-PHA, CM-pokeweed mitogen) nonspecifically enhanced normal basophilopoiesis, causing dose-dependent increases in basophils and histamine in vitro. CM-OA and CM-PHA also preferentially stimulated formation of neutrophil-macrophage colony-forming units in semisolid methylcellulose cultures.CM-PHA prepared from T cell-enriched splenic cell suspensions contained basophil-stimulating activity, whereas T cell-depleted CM-PHA activity did not exceed control values (P < 0.01). Preliminary characterization of CM-PHA revealed that basophil-stimulating activity was predominantly heat stable and nondialyzable. These results demonstrate OA-specific, as well as mitogen-dependent T-cell regulation of guinea pig basophilopoiesis in vitro. The data are compatible with the existence of a specific "basophilopoietin" in CM derived from guinea pig splenic T cells.