Acanthamoeba keratitis primes humoral but not cellular immune responses

Purpose. To determine if Acanthamoeba keratitis induces cell-mediated and humoral immunity to parasite antigens. Methods. Corneas of Chinese hamsters were infected with Acanthamoeba castellanii-laden contact lenses. Seven days later hosts were immunized intramuscularly (IM) with parasite antigen. Delayed-type hypersensitivity (DTH) and serum IgG antibody responses were evaluated 14 days later. Langerhans cells (LC) were induced into the central cornea by instilling latex beads into the corneal epithelium prior to infection. Results. Infection of Langerhans cell negative (LC^-) corneas failed to induce serum IgG antibody or DTH responses (P=0.35). However, infection of LC⁺ corneas produced IgG antibody and DTH responses that were significantly greater (P< 0.05) than normal controls and hosts infected via LC^- corneas. Hosts infected via LC^- corneas were subsequently immunized IM and immune responses re-evaluated to determine if infection had induced tolerance. Results indicated that infection of LC^- corneas primed the host's B cells since antibody titers were indicative of an anamnestic response. Although DTH was induced by IM immunization, it was indicative of a primary, rather than a secondary response (P< 0.05). Conclusions. The absence of corneal LC prevents complete induction of humoral and cellular immunity to corneal infection with Acanthamoeba. This is not due to tolerance but appears to be the result of partial priming of B cells and a null event for DTH effector cells.