In normal hen ovary S1P1 expression was observed in areas of immune cell infiltration. (Row A) Immune cells (Bu1a+ and CD3+) are adjacent to the follicle (f) in the ovarian stroma near a transverse blood vessel (arrow in column S1P1). Cells lining the vessel near the follicle (f) are S1P1+ (row A, S1P1) (original magnification 100×). (Row B) High magnification (see red boxes in row A) showing B and T cells clustered within the stroma near S1P1 stained vascular endothelium (arrow). Some immune cells are also S1P1+ (open arrow) (original magnification 400×). (Row C) Cross-section of a large blood vessel shows Bu1a and CD3 positive cells are clustered near the blood vessel. The apical surfaces of endothelial cell express S1P1 (original magnification 100×).