Chemokine expression and fetal thymus colonization in Foxn1-deficient mice. Sagittal sections of frozen embryos from indicated mice of BALB/c background were 2-color stained for CCL21 (Alexa 633, red) and keratin (FITC, blue) (A-D), CCL25 (Alexa 633, red) and keratin (areas surrounded by dashed lines indicate keratin-positive areas) (E-H), or CD45 (Alexa 633, green) and keratin (FITC, red) (I-L). Control IgG staining shows the specificity of CCL21 and CCL25 signals (M-P). Anterior-posterior (a-p) and dorsal-ventral (d-v) orientation of the images is indicated. The means plus or minus standard errors of the numbers of CD45⁺ cells in and attached to the third pharyngeal pouch region that contains the thymic primordium are shown in panels Q and R. ^***P < .001; NS, not significant.