Immunohistochemical study of tyrosine phosphorylation signaling in Hassall's corpuscles of the human thymus

A phase II study of saracatinib (AZD0530), a Src inhibitor, administered orally daily to patients with advanced thymic malignancies

OBJECTIVES

Thymic malignancies are rare, and options are limited for metastatic disease. Src plays a role in normal thymic epithelial maturation, and its inhibition with the oral compound saracatinib was postulated to be effective in controlling thymic malignancy.

MATERIALS AND METHODS

Patients with unresectable thymic malignancy were treated with saracatinib 175mg by mouth daily in 28 days cycles with radiographic evaluation at cycle 2 day 1 for safety, then cycle 3 day 1 and every 8 weeks thereafter. Response was evaluated by RECIST 1.0. A two-stage optimal design was used, powered to detect a true response rate of 20%.

RESULTS

21 patients were enrolled at two institutions, 12 of them with thymoma, 9 with thymic carcinoma. Thymoma patients received a median of 4.5 cycles and thymic carcinoma patients a median of 1 cycle. There were no responses, so accrual was halted after the first stage per protocol. 9 patients had stable disease beyond the first assessment. Median time to progression was 5.7 months for thymoma patients and 3.6 months for thymic carcinoma patients. Saracatinib was well tolerated.

CONCLUSION

Src inhibition by saracatinib did not produce any radiographic responses, though some patients did experience stable disease. Though negative, this study shows the feasibility of completing a trial in this rare disease, and of accruing reasonably significant numbers of thymic carcinoma patients. More clinical trials are required for this population (NCT00718809).

Immunohistological analysis of the jun family and the signal transducers and activators of transcription in thymus

The Jun family and the signal transducers and activators of transcription (STAT) are involved in proliferation and apoptosis. Moreover, c-Jun and STAT3 cooperate to regulate apoptosis. Therefore, we used double immunostaining to investigate the immunotopographical distribution of phospho-c-Jun (p-c-Jun), JunB, JunD, p-STAT3, p-STAT5, and p-STAT6 in human thymus. JunD was frequently expressed by thymocytes with higher expression in medullary compared to cortical thymocytes. p-c-Jun was frequently expressed by cortical and medullary thymic epithelial cells (TEC) and Hassall bodies (HB). p-STAT3 was frequently expressed by TEC with higher expression in cortical compared to medullary TEC and HB. p-c-Jun, JunB, p-STAT3, p-STAT5, and p-STAT6 were rarely expressed by thymocytes. JunB and JunD were expressed by rare cortical TEC with higher expression in medullary TEC. p-STAT5 and p-STAT6 were expressed by rare cortical and medullary TEC. Double immunostaining revealed p-c-Jun and JunD expression in rare CD11c positive dendritic cells. Our findings suggest a notable implication of JunD in the physiology of thymocytes and p-c-Jun and p-STAT3 in the physiology of TEC. The diversity of the immunotopographical distribution and the expression levels of p-c-Jun, JunB, JunD, p-STAT3, p-STAT5, and p-STAT6 indicates that they are differentially involved in the differentiation of TEC, thymocytes, and dendritic cells.

Thymic epithelial cells in age-dependent involution

Aging involves morphological and functional alterations within the microenvironment of the thymus where heterogenous populations of thymic epithelial cells (TEC) play the main roles. The studies performed to date on thymic involution signalize a disturbed interaction between individual thymic compartments that disrupt thymocyte-TEC interactions and, as a sequele, disturb differentiation of both TEC and thymocytes. The process of aging affects the various subsets of TEC at different periods of life. Changes in different subsets of TEC are documented on the basis of their phenotypical characteristics, involving morphological analysis and immunocytochemistry. The character and kinetics of changes in TEC are typical for individual subsets and probably sex-dependent. In the course of life, the involutionary changes, expressed by disorganised thymic structure and function, are accompanied by changes in medullary TEC, manifested by alterations in the differentiation process of the cells. In parallel, at the same stage of individual life, the aging process induces increased proliferative and secretory activity of subseptal TEC, which seem to functionally replace medullary TEC. Structural and phenotypic modifications of TEC are locally controlled by complex sets of different factors and seem to represent a morphological adaptation of the gland to the process of aging. Microsc. Res. Tech. 62:488-500, 2003.

The Goodpasture antigen is expressed in the human thymus

BACKGROUND

Autoimmunity to kidney antigens causes membranous nephropathy and Goodpasture's disease and very likely is pivotal in many other glomerular diseases. We investigated the potential for central tolerance to the best-characterized kidney autoantigen, the NC1 domain of the alpha3 chain of type IV collagen [alpha3(IV)NC1], which is the target of autoimmune attack in Goodpasture's disease.

METHODS

Indirect immunofluorescence on human thymus and polymerase chain reaction (PCR) and Southern blot analysis of cDNA reverse transcribed from RNA extracted from human thymus and kidney.

RESULTS

Indirect immunofluorescence on human thymus demonstrated the presence of alpha3(IV)NC1 in all six thymus samples examined. The homologous collagen IV chain, alpha5(IV)NC1, also was detected with a similar intra-thymic distribution. Strikingly, thymic alpha3 and alpha5 localized around and within Hassall's corpuscles in the thymic medulla, which are structures implicated in T cell apoptosis and possibly negative selection. In contrast, alpha1(IV)NC1 localized to the basement membranes of interlobular septa and blood vessels, as is typical of collagen IV chains situated outside the thymus. Reverse transcription-polymerase chain reaction (RT-PCR) confirmed the presence of mRNA encoding alpha3(IV)NC1 and alpha5(IV)NC1 in thymic tissue establishing that the antigens were likely to have been synthesized locally.

CONCLUSIONS

The results demonstrate that alpha3(IV)NC1 is expressed in the human thymus, and therefore should be available for induction of alpha3(IV)NC1-specific tolerance. This observation has the important implication that patients' alpha3(IV)NC1-specific, autoreactive T cells are more likely to recognize cryptic epitopes that are not adequately presented by thymic antigen-presenting cells (APC) than the major antigen-derived epitopes generally identified by conventional approaches.

Immunolocalisation of the janus kinases (JAK)--signal transducers and activators of transcription (STAT) pathway in human epidermis

The janus kinases (JAK) and signal transducers and activators of the transcription (STAT) pathway have been shown to be activated by a number of cytokines or growth factors and to play significant roles in the differentiation of various cell types. In the present study, we investigated the distribution of the JAK-STAT pathway using immunohistochemistry in the human epidermis. Each element of the pathway showed abundant and differential expression in the epidermis. The differential distribution of the elements was most strikingly observed in the horny keratinised cell and granular layers of the epidermis. JAK2, JAK3, STAT1 and STAT5 were expressed in high amounts, and JAK1, TYK2, STAT2, STAT3, STAT4 and STAT6 to a much lesser extent in the horny cell layer. JAK3, TYK2, STAT2, STAT3, STAT4 and STAT6 were more abundantly expressed in the granular layer than the lower layers of the epidermis. JAK1, STAT1 and STAT5 were expressed at almost the same levels in the various layers of the epidermis. These results show that elements of the JAK-STAT pathway are abundantly and differentially expressed in the epidermis. It is suggested that each element of the pathway may play a role at a distinct stage of keratinocyte differentiation.

Immunolocalization of the mitogen-activated protein kinase signaling pathway in Hassall's corpuscles of the human thymus

In the present study, we investigated the immunohistochemical localization of mitogen-activated protein kinase (MAPK) signaling pathway in the human thymus. Three members of MAPK, the extracellular signal-regulated kinase (ERK), the c-Jun N-terminal kinase (JNK) and the p38 kinase, showed differential expression patterns in the thymus medulla. The phosphorylated form of ERK (p-ERK) was abundantly present in the outer layer of Hassall's corpuscles, and the phosphorylated form of p38 kinase (p-p38 kinase) was present in the entire Hassall's corpuscles. The phosphorylated form of JNK (p-JNK) was expressed in medullary thymocytes. We also examined localization of MAPK kinases (MAPKK or MEK) which specifically activate MAPK. MEK1, an activator of ERK, was found in the outer layer of Hassall's corpuscles where p-ERK was expressed. MEK3, an activator of p38 kinase, was also expressed in the outer layer. MEK4 and MEK7, which are activators of JNK, were present in the entire Hassall's corpuscles. Thus, differential expression of MAPK in the thymus supports the concept that the MAPK signaling pathway controls the specificity of functional thymic responses to extracellular stimuli. Furthermore, the abundant expression of various elements of the pathway in Hassall's corpuscles suggests that the pathway is involved in thymic medullary epithelial maturation.