Constitutive IFN-a Expression in the Human Thymus Figure 2. MxA is expressed in the thymic medulla. Postnatal thymus tissue was formalin fixed and paraffin embedded. 4 um sections were mounted on slides. A, Thymus tissue was stained with CD1a and MxA followed by Goat anti-mouse IgG1 Alexa Fluor 488 and Goat anti-mouse IgG2a Alexa Fluor 594. B, Thymus tissue was stained with antibodies directed against CD27 and MxA followed by Goat ant-mouse IgG1 Alexa Fluor 488 and Goat anti-mouse IgG2a Alexa Fluor 594. doi:10.1371/journal.pone.0024252.g002 Figure 3. MxA is preferentially expressed in mature thymocytes and exogenous IFN-a only upregulates MxA in immature CD1a+CD272 thymocytes. A, B, Total thymocytes were stained for surface expression of CD4, CD8, CD1a, CD3, CD27, CD45RA and CD123 combined with intracellular MxA expression. A, Differences of thymocyte subset expression patterns in all thymocytes, MxA negative and positive cells are shown. B, Differences of thymocyte subset expression patterns in CD27+, MxA negative and positive cells are shown. C, Total thymocytes were cultured in the presence or absence of 1000 U/mL IFN-a overnight. Cells were stained for surface expression of CD4, CD8, CD1a, CD3, CD27, CD45RA and CD123 combined with intracellular MxA expression. MxA expression in immature and mature thymocyte subsets was determined by gating on CD1a+CD272 and CD1a2CD27+ cells respectively. doi:10.1371/journal.pone.0024252.g003 PLoS ONE | www.plosone.org 5 August 2011 | Volume 6 | Issue 8 | e24252