Louis Kater

Effects of human thymic epithelial-conditioned medium on mitogen responsiveness of human and mouse lymphocytes.

The conditioned media from a variety of human tissue cultures, thymus, HeLa cells, labial epithelium, salivary glands, and fibroblasts, were examined for their effect on the response of human and mouse lymphocytes to mitogens. Conditioned media from thymus epithelial cultures (HTECM), but not from nonthymic epithelial cultures and fibroblasts, increased [3H]TdR incorporation into Con A- and PHA-stimulated thymocytes of man and mouse. No effect was seen on B lymphocytes. Target cells for HTECM were not found in human peripheral blood lymphocytes. In the mouse target cells were found in two thymocyte subpopulations, the cortisone-resistant and cortisone-sensitive, and in the spleen. Lymph node cells contained no target cells.

Presence of thymosin-like factors in human thymic epithelium conditioned medium

The objective of the present study was to determine whether or not thymosin and conditioned medium from human thymus epithelial cultures (HTECM) contain similar fractions, capable of inducing T-cell differentiation. Therefore we tested the ability of rabbit antisera to different thymosin fractions (thymosin fractions 5, 6 and alpha 1) of both bovine and human origin to block the stimulatory effect of HTECM on Con A and PHA response of mouse thymocytes. We also looked for reactivity of the antisera toward tissues of man, mouse and calf, and to tissue cultures of man and mouse. Anti-thymosin fraction 5 and 6, but not anti-thymosin-alpha 1, were found to inhibit the stimulatory effect of HTECM on both Con A and PHA responses. This cannot be attributed to cytostatic or cytotoxic effects of the antisera on thymocytes. No effect was seen when using antiserum to kidney fraction 5 or normal rabbit serum. In both tissue sections and tissue cultures of the different species tested, anti-thymosin reacts only with thymus epithelial cells. The reactivity is blocked by neutralizing the antisera with thymosin fraction 5 but not by kidney fraction 5. The reactivity is also strongly diminished by neutralizing the antisera with HTECM but not with supernatants of conditioned media from non-thymic tissues. The observations are highly suggestive for the presence of similar fractions in HTECM and thymosin, and that both are secreted by thymus epithelial cells.

How unique is the thymus? Conditioned media from thymus and tonsil epithelial cultures share biological activities in T-cell maturation.

Abstract Thymic factors, probably derived from thymus epithelial cells, are known for their capacity to induce T-cell maturation. One of these factors, human thymic epithelial conditioned medium (HTECM), is able to increase responsiveness of human and mouse thymocytes to concanavalin A (Con A) and phytohemagglutinin (PHA), mixed lymphocyte culture (MLC) reactivity, cell-mediated cytotoxicity (CMC), and in vivo graft-versus-host reactivity of mouse thymocytes. Conditioned media from human thymocytes, from epithelial cultures from nonlymphoid organs, and from fibroblast cultures fail to do so. We explored whether the activity found in HTECM is specific for the thymus or can be found to be a property of conditioned media from epithelial cultures of lymphoepithelial organs. It appeared that conditioned medium from tonsil epithelial cultures enhanced the mitogen responsiveness, MLC reactivity, and CMC response in the same way as described for HTECM. We therefore conclude that conditioned media from human thymus and tonsil epithelial cultures share biological activities in T-lymphocyte maturation in vitro.

The thymus in the aging individual: I. Mitogen responsiveness of human thymocytes

Abstract A decrease in thymus function has been observed in aging individuals. This may be due to changes either in the thymocyte population or in the thymus microenvironment. A function of the latter is secretion of thymic factors, one of which is human thymic epithelial-conditioned medium (HTECM). In this study we have investigated the responsiveness of human thymocytes from individuals of different age to mitogens and the effect of HTECM upon this response. The responsiveness of human thymocytes to Con A and PHA increased with advancing age, and was most prominent for PHA. This increase could not be attributed to changes in monocyte numbers. Thymocytes sensitive to HTECM modulation with Con A as mitogen were found in all age groups. With PHA as mitogen only thymocytes from individuals under the age of 8 years were sensitive to HTECM. The results can be explained by a relative increase of the more mature, medullary thymocytes in the thymus with age.

Effect of Human Thymic Epithelial Conditioned Medium on in Vitro and in Vivo Alloantigen-Induced Lymphocyte Activation in the Mouse

Human thymic epithelial conditioned medium (HTECM), but not control conditioned media, has been shown previously to enhance the Con A and PHA responsiveness of human and mouse thymocytes and the PHA response of spleen cells. In this study we have demonstrated that HTECM increased the reactivity of mouse thymocytes in oneway mixed lymphocyte culture and in cell-mediated cytotoxicity, while no enhancing effects were observed with spleen cells. Incubation of mouse thymocytes with HTECM rendered the cells more reactive in in vivo graft versus host reactions. The findings indicate that HTECM, an in vitro produced factor of the human thymus, plays an important role in the induction of immunocompetence in thymocytes.

The thymus in the aging individual: II. Thymic epithelial function in vitro in aging and in thymus pathology

Abstract Thymus function decreases with aging. This is accompanied by changes in thymocyte composition, related to different rates of involution of cortex and medulla. One cause may be an improper microenvironment for T-cell differentiation. A function of the thymus microenvironment is secretion of thymic factors, one of which is human thymic epithelial-conditioned medium (HTECM). In this study we investigated whether activity of HTECM on mitogen response of mouse thymocytes could be related to the age of the thymus donor. The activity of HTECM appeared to be highest when obtained from thymic epithelial cultures of donors around 20 years; thereafter the effect of HTECM declined. HTECM obtained from epithelial cultures of pathologic thymus tissue displayed various effects. HTECM from hyperplastic thymus showed the same or high activity related to that from age-matched normal thymus. HTECM derived from cultured thymic tumors gave no to very high activity.

Studies on the mechanism of action of human thymic epithelial conditioned medium on mouse thymocytes. Evidence for induction of immune competence

It has been shown that addition of human thymic epithelial conditioned medium (HTECM) leads to an increased response of mouse thymocytes to concanavalin A and phytohemagglutinin. HTECM caused a maximal potentiating effect when added to thymocyte cultures at the time of their initiation. Addition at later times had a smaller enhancing effect and after 24 hr no effect of HTECM could be measured. Responses to mitogen were higher at all time periods measured and peak responses were shifted to later times in the presence of HTECM. Determination of cell viability made it highly unlikely that the effect of HTECM was simple due to enhanced numbers of viable cells in culture. These data support the view that HTECM induces T-lymphocyte maturation.