Anat Cell Biol.  2011 Mar;44(1):14-24. 10.5115/acb.2011.44.1.14.

Characterization of the expression of cytokeratins 5, 8, and 14 in mouse thymic epithelial cells during thymus regeneration following acute thymic involution

• Lee EN
• Park JK
• Lee JR
• Oh SO
• Baek SY
• Kim BS
• Yoon S

• KMID: 2168864
• DOI: http://doi.org/10.5115/acb.2011.44.1.14

Abstract

The thymus is a central lymphoid organ for T cell development. Thymic epithelial cells (TECs) constitute a major component of the thymic stroma, which provides a specialized microenvironment for survival, proliferation, and differentiation of immature T cells. In this study, subsets of TECs were examined immunohistochemically to investigate their cytokeratin (CK) expression patterns during thymus regeneration following thymic involution induced by cyclophosphamide treatment. The results demonstrated that both normal and regenerating mouse thymuses showed a similar CK expression pattern. The major medullary TECs (mTEC) subset, which is stellate in appearance, exhibited CK5 and CK14 staining, and the minor mTEC subset, which is globular in appearance, exhibited CK8 staining, whereas the vast majority of cortical TECs (cTECs) expressed CK8 during thymus regeneration. Remarkably, the levels of CK5 and CK14 expression were enhanced in mTECs, and CK8 expression was upregulated in cTECs during mouse thymus regeneration after cyclophosphamide-induced acute thymic involution. Of special interest, a relatively high number of CK5+CK8+ TEC progenitors occurred in the thymic cortex during thymus regeneration. Taken together, these findings shed more light on the role of CK5, CK8, and CK14 in the physiology of TECs during mouse thymus regeneration, and on the characterization of TEC progenitors for restoration of the epithelial network and for concomitant regeneration of the adult thymus.

Keyword

Cytokeratin; Thymic epithelial cell; Thymic epithelial progenitor; Thymus regeneration

MeSH Terms

Adult
Animals
Cyclophosphamide
Epithelial Cells
Humans
Keratins
Light
Mice
Regeneration
T-Lymphocytes
Thymus Gland
Cyclophosphamide
Keratins

Figure

• 

  Fig. 1 (A-D) Immunohistochemical localization of cytokeratin (CK)5 in frozen sections of mouse thymus from control animals (A1-3, n=4), and at 3 (B1-3, n=7), 7 (C1-3, n=6), and 14 (D1-3, n=4) days after cyclophosphamide treatment. C, cortex; M, medulla; arrows, CK5+ thymic epithelial cells. Scale bars=100 µm (A1, B1, C1, D1), 50 µm (A2, A3, B2, B3, C2, C3, D2, D3). (E) Data on the relative intensity of CK5 expression in the thymic medulla are also plotted in a bar graph and expressed as mean±standard deviation. CY 3d, CY 1w, and CY 2w represent 3, 7, and 14 days after cyclophosphamide treatment, respectively. *P<0.001 compared with the control, as determined by the t-test.

• 

  Fig. 2 (A-D) Immunohistochemical localization of cytokeratin (CK)14 in frozen sections of mouse thymus from control animals (A1-3, n=4), and at 3 (B1-3, n=7), 7 (C1-3, n=6), and 14 (D1-3, n=4) days after cyclophosphamide treatment. C, cortex; M, medulla; arrows, CK14+ thymic cortical epithelial cells. Scale bars=100 µm (A1, B1, C1, D1), 50 µm (A2, A3, B2, B3, C2, C3, D2, D3). (E) Data on the relative intensity of CK14 expression in the thymic medulla are also plotted in a bar graph and expressed as mean±standard deviation. CY 3d, CY 1w, and CY 2w represent 3, 7, and 14 days after cyclophosphamide treatment, respectively. *P<0.001 compared with the control, as determined by the t-test.

• 

  Fig. 3 (A-D) Immunohistochemical localization of cytokeratin (CK)8 in frozen sections of mouse thymus from control animals (A1-3, n=4), and at 3 (B1-3, n=7), 7 (C1-3, n=6), and 14 (D1-3, n=4) days after cyclophosphamide treatment. C, cortex; M, medulla. Scale bars=100 µm (A1, B1, C1, D1), 50 µm (A2, A3, B2, B3, C2, C3, D2, D3). (E) Data on the relative intensity of CK8 expression in the thymic cortex are also plotted in a bar graph and expressed as mean±standard deviation. CY 3d, CY 1w, and CY 2w represent 3, 7, and 14 days after cyclophosphamide treatment, respectively. *P<0.001 compared with the control, as determined by the t-test.

• 

  Fig. 4 High magnification images of the stellate and globular thymic medullary epithelial cells (mTECs) by immunohistochemical localization of cytokeratin (CK)5, CK8, and CK14 in frozen sections of the mouse thymus from control animals. (A, B) CK5 and CK14 immunoreactivity was observed in virtually all of the stellate mTECs, whereas thymic cortical epithelial cells (cTECs) barely expressed CK5 and CK14 in the thymic cortex of normal mice. (C) CK8 was expressed by a minor subset of mTECs, most of which are globular in appearance, in the thymic medulla of control mice, whereas all the cTECs expressed CK8 in the thymic cortex of normal mice. C, cortex; M, medulla; arrows, CK8+ globular mTECs. Scale bars=50 µm.

• 

  Fig. 5 (A) Two-color double-label immunofluorescent localization of cytokeratin (CK)8 (green) and CK5 (red) in frozen sections of mouse thymus 3 days after cyclophosphamide treatment. C, cortex; M, medulla; arrows, CK5+CK8+ thymic epithelial cells. Scale bar=50 µm. Data on the relative number of CK5+CK8+ (B) and CK14+CK8+ (C) Cotical thymic epithelial cells (cTECs) are also plotted in a bar graph and expressed as mean±standard deviation. *P<0.001 compared with the control, as determined by the t-test.

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