The histopathology of experimental trachoma: ultrastructural changes in the conjunctival epithelium

Experimental acute conjunctivitis was produced in cynomolgus monkeys by ocular inoculation with serovar B of Chlamydia trachomatis. The cellular responses to chlamydial conjunctivitis infection were examined by light, transmission, and scanning electron microscopy. A self-limited, acute conjunctivitis resulted from a single primary inoculation. A moderate lymphocytic infiltrate was present in the conjunctiva. After repeated inoculation, a chronic conjunctivitis (trachoma) developed. Prominent lymphoid follicles with distinct germinal centers were present in these tissues. Scanning electron microscopy revealed patchy areas of cellular alteration and loss of microvilli. Intracellular injury, documented by transmission electron microscopy, included disruption of the plasmalemmal membranes and rupture of the cytoplasmic organelles. The inflammatory infiltrate consisted of plasma cells, polymorphonuclear cells, lymphocytes, eosinophils, and degranulating mast cells. The immune response following single and repeated chlamydial infections was characterized by immunoperoxidase staining with monoclonal antibodies to pan-leukocytes, macrophages, and B cells. The center of the follicle was comprised of B cells, with T cells in the cap region. Large macrophages were also found in the germinal center. Further study is required to determine which cellular mechanisms are involved in the histopathologic and immunologic alterations induced in the conjunctiva after chlamydial infection.