Antibodies to Recoverin Induce Apoptosis of Photoreceptor and Bipolar Cellsin vivo

Abstract

Autoantibodies against recoverin are found in the sera of patients with cancer-associated retinopathy (CAR) syndrome. In these studies we examined the effect of anti-recoverin antibodies from the sera of patients with CAR and rat monoclonal antibody on the retinas of Lewis rats. Anti-recoverin autoanti-bodies penetrated into the photoreceptor and bipolar cell layers following intravitreal injection. Their presence in the retina could be detected by immunofluorescence 24h after injection. At the same time, individual cells undergoing apoptosis were identified throughout photoreceptor and bipolar cell layers using terminal transferase-mediated dUTP nick-end labeling (TUNEL) and electron microscopy. Normal antibodies used in control experiments did not produce TUNEL labeling. At 24h, DNA fragmentation was confirmed by DNA ladder electrophoresis. At the electron microscopic level, there was clear evidence of cells undergoing apoptotic cell death in the retinas treated with anti-recoverin antibodies. At 24 and 96h, nuclear chromatin condensation and increased vacuolization of photoreceptor outer segments were observed. An examination of retinas from animals receiving anti-retinal antibodies revealed a loss of 1–2 rows of nuclei in the outer and inner nuclear layers whereas all controls (sham, normal IgG, phosphate buffered saline) showed an unchanged number of nuclei rows. In addition, there was an increase in spacing between the rows of nuclei of the outer nuclear layer in retinas treated with anti- recoverin antibodies, indicating additional cell loss. These studies provide clear evidence that anti-recoverin antibodies are capable of penetrating photoreceptor and bipolar cells, the normal site of recoverin expression in the retina, and that anti-recoverin antibodies produce apoptotic cell death. A similar mechanism may occur in patients with CAR, which may lead to visual loss and blindness.