**4. Conclusions**

*Thymus*

**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

*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* 

**108**

**Figure 3.**

**Figure 2.**

*medulla (M) but also in the cortex (Co).*

*Density means of 3-NT cells in the thymus (density mean ± SEM of pixels/mm2*

*V-exposed mice from week 1 to week 4. ANOVA (Tukey' s) p* ≤ *0.05.*

*). Density values increased in* 

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 polluted cities [39].
