An evaluation of the role of leukocytes in the pathogenesis of experimentally induced corneal vascularization.

Studies of corneal explants in the hamster cheek pouch chamber have demonstrated that blood vessels invade the cornea only if the tissue is first infiltrated by leukocytes. In view of this observation, a comparative study of the events that precede and accompany corneal vascularization was undertaken in various experimental models. A variety of established methods were used to induce corneal vascularization, including exposure of the cornea to noxious agents, intracorneal injection of antigens into sensitized animals, as well as maintaining animals on diets deficient in vitamin A or riboflavin. In all models studied, the corneal vascularization was a manifestation of the reparative phase of the inflammatory response. A conspicuous leukocytic infiltrate of the cornea preceded and accompanied the corneal vascularization in all of the models. Although the lesions varied in several respects in the different models, all models displayed three phases with regard to vascularization: an early prevascular phase of leukocytic infiltration, a second phase where blood vessels persisted in the cornea in the absence of leukocytes. The latent period that preceded vascularization was directly related to the time of the initial leukocytic infiltration. The models in which a delay occurred in the leukocytic invasion displayed a subsequent delay in the vascular ingrowth. Conversely, in experiments where there was a rapid and extensive leukocytic invasion, there was also an early and enhanced corneal vasoproliferative response. In the various modesl investigated, the sites of the leukocytic infiltration and subsequent vascular ingrowth into the cornea paralleled each other. The data further support the hypotheses that leukocytes are a prerequisite to corneal vascularization and that leukocytes produce one or more factors which stimulate directional vascular growth.