Mucosal penetration of antigen in the presence or absence of serum-derived antibody: An in vitro study of rabbit oral and intestinal mucosa

Rabbit mucous membranes were mounted in diffusion chambers within 30 min after excision. The epithelial side was exposed to cell culture medium containing `cold' and 125I-labelled human albumin. The basal side was exposed to normal rabbit serum (control chambers) or to rabbit anti-serum against human albumin. The chambers were incubated in a humidified atmosphere of CO2 in air for 2–3 h at 37°. The radioactive material recovered on the basal side of the sublingual control membranes sedimented virtually like native albumin on ultracentrifugation. The amount of radioactive material recovered after penetration through anti-serum-exposed sublingual mucosa was reduced by 50–80% and showed a very heterogeneous sedimentation pattern including aggregates, presumably immune complexes, as well as a considerable amount of degradation products. In a second series of experiments the concurrent penetration of human albumin and transferrin through the sublingual mucosa of rabbits immunized parenterally with albumin was compared with that occurring through control membranes. With reference to immunochemical quantification, scintillation counting was found to overestimate the penetration of intact albumin considerably, and jeopardized evaluation of the influence of serum-derived antibody. Radial immunodiffusion showed that in controls the basal antigen concentration, expressed in percentage of the oral (30 mg/ml for both molecules), was after 2 h 0.0032±0.0023 for albumin and 0.0016±0013 for transferrin. Penetration of immunoreactive albumin through mucosa from immunized animals was clearly reduced (0.0007±0.0003), whereas there was a significant tendency toward increased penetration of transferrin (0.0035±0.0023). These results suggest that antibody within the mucosa retards the penetration of intact homologous antigen, while immune reactions may enhance the penetration of unrelated macromolecules. In similar experiments with colon mucosa penetration was 50–100 times increased, but the membranes did not discriminate between albumin and transferrin and there was no effect of immunization. Histological and immunohistochemical studies of the latter membranes indicated marked defects in cell viability after 2 h in vitro.