PECAM-1^−/− mice develop detectable ANAs and autoimmune disease with age.

PECAM-1^−/− (n = 8) and wild-type (PECAM-1^+/+) (n = 8) mice were maintained in a barrier-protected facility and bled on a monthly basis over a 17-month period. Serum samples were analyzed from an initial 1:50 dilution on HEp-2000 cell substrates and ANAs detected with antimouse FITC. (A) Photomicrograph of a negative wild-type and positive PECAM-1^−/− sera obtained from a PECAM-1^−/−mouse at 9 months of age. The PECAM-1^−/− sera produced a homogeneous staining pattern of the cell nuclei (magnification × 132). (B) End-point serum dilutions of all serum samples from PECAM-1^+/+ and PECAM-1^−/− mice at 17 months of age. (C) ELISA readings of IgG antibodies to dsDNA for sera obtained from PECAM-1^+/+ (front row) (n = 4) and PECAM-1^−/− (back row) (n = 4) mice at 9 months of age. Values are representative of triplicate experiments. (D) Frozen kidney sections of PECAM-1^+/+ (n = 8) and PECAM-1^−/− (n = 8) were stained for hematoxylin and eosin (magnification × 132) and immune complex deposition by immunofluorescence with FITC–antimouse IgG (Fab′₂) (magnification × 132). This figure shows representative hematoxylin and eosin and immunofluorescence stains of frozen kidney sections from 17-month-old PECAM-1^+/+ and PECAM-1^−/− mice. All slides were photographed and reproduced with identical times, microscope settings, and exposure times, thereby ensuring that the background was equivalent across all photographs shown.