**3.3 Thymic epithelial cells**

Previous studies have demonstrated the interdependence of TEC and the thymocytes to maintain the thymic microenvironment integrity. TEC are APCs distributed in the cortex (cTEC) and in the medullae (mTEC). cTEC select the thymocytes that express TCR and recognize self-MHC. The remaining cells are eliminated by apoptosis; this positive selection takes place in the cortex. mTEC with DCs are in charge of the negative selection of T cells and to establish central tolerance, as well as helping to regulate the production of regulatory T cells (Treg) [26, 27]. Previous studies from our group have demonstrated that V exposure change the thymic

#### **Figure 2.**

*K5 expression in the thymus. Representative photomicrographs from: (A) control and (B) 2-week-V-exposed. Positive K5 cells are located in the medullae (M) and some in the cortex (Co), B. K5+ cells located in the medulla (M) but also in the cortex (Co).*

**109**

**Author details**

(3-NT) [38].

**4. Conclusions**

polluted cities [39].

thymus tissue of 3-NT (**Figure 3**).

Martha Ustarroz-Cano, Marisol López-Ángel, Nelly López-Valdez,

Autonomous University of Mexico (UNAM), Mexico City, México

Department of Cellular and Tissular Biology, School of Medicine, National

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Isabel García-Peláez and Teresa I. Fortoul\*

provided the original work is properly cited.

\*Address all correspondence to: fortoul@unam.mx

*The Effect of Atmospheric Pollution on the Thymus DOI: http://dx.doi.org/10.5772/intechopen.87027*

cortex/medullae ratio and by using cytokeratin-5 (K5) as a marker, the mistaken location of the K5+ cells in the medulla was demonstrated **Figure 2** [4, 30].

The density mean showed the changes in the presence of K5+, ocher-stain cells that increased during the first week of exposure compared with controls; however, the stain density at weeks 2 and 4 had a slight decrease but never reached the control values p < 0.05. These results showed that V produced changes in thymus cytoarchitecture, in addition of an increase in K5+ cells, changes that suggest that the T-cell selection was disrupted by V-inhalation [5]. Also, the presence of nitrosative stress as possible explanation of our findings was explored with 3-nitrotyrosine

Our unpublished data demonstrated an increase time-dependent in the whole

Air pollution affects the thymus. V inhalation induces nitrosative stress a decrease in DCs, the expression of CD11c and MHCII and mTEC increase, which could implicate that the negative and the positive selection were not properly completed. All these changes could allow that autoreactive clones were liberated to the blood stream and the incidence in autoimmune diseases rises in the dwellers of

**Figure 3.**

*Density means of 3-NT cells in the thymus (density mean ± SEM of pixels/mm2 ). Density values increased in V-exposed mice from week 1 to week 4. ANOVA (Tukey' s) p* ≤ *0.05.*

*The Effect of Atmospheric Pollution on the Thymus DOI: http://dx.doi.org/10.5772/intechopen.87027*

cortex/medullae ratio and by using cytokeratin-5 (K5) as a marker, the mistaken location of the K5+ cells in the medulla was demonstrated **Figure 2** [4, 30].

The density mean showed the changes in the presence of K5+, ocher-stain cells that increased during the first week of exposure compared with controls; however, the stain density at weeks 2 and 4 had a slight decrease but never reached the control values p < 0.05. These results showed that V produced changes in thymus cytoarchitecture, in addition of an increase in K5+ cells, changes that suggest that the T-cell selection was disrupted by V-inhalation [5]. Also, the presence of nitrosative stress as possible explanation of our findings was explored with 3-nitrotyrosine (3-NT) [38].

Our unpublished data demonstrated an increase time-dependent in the whole thymus tissue of 3-NT (**Figure 3**).
