Source of IgA in tears of rats

The purpose of the present study was to determine whether IgA in rat tears originates from serum and/or local synthesis. To examine the first possibility, we compared the IgA levels in serum and tears of rats with a portacaval anastomosis. This operation induced a chronic and progressive elevation of polymeric IgA concentrations in serum. By 8 weeks after surgery, serum IgA levels in 'portacaval' rats were 20-fold higher than those of sham-operated or intact controls. In contrast, IgA levels in tears of 'portacaval' rats did not increase after surgery, despite the availability of free secretory component (SC) in tears. The lack of correlation between tear and serum IgA concentrations resulted in a significant decrease in the tear IgA/serum IgA ratio after anastomosis surgery. To assess whether tear IgA might be derived from local synthesis, we cultured various ocular tissues from male rats in the presence or absence of cycloheximide, an inhibitor of protein synthesis. Incubation of exorbital (lacrimal) glands resulted in the accumulation of substantial quantities of IgA in the culture medium. This accumulation was significantly reduced by the presence of cycloheximide. In contrast, cycloheximide had no effect on the amounts of IgA in cultures of 'lids', Harder's glands and globes. These results indicate that IgA in rat tears originates from local synthesis and not from serum transfer. Furthermore, our findings suggest that the rat exorbital gland is responsible for the synthesis and secretion of tear IgA.