Relationship between polypeptide transcytosis and lymphoid tissue in the rabbit nasal mucosa.

It has been suggested that the specific transcytosis of polypeptides, demonstrated in rabbit nasal mucosa (upper concha), is involved in antigen sampling at the airway entry. To test this hypothesis, unidirectional transepithelial fluxes of carbocalcitonin (CCT Mw = 3362) from the mucosal to the submucosal side, and vice versa, were measured by radioimmunoassay every 30 min for 120 min and, from the difference, net absorption was determined in the upper concha and septum mucosae. The exposed mucosae were examined by quantitative histology; isolated scattered lymphoid cells/mm2 and volumes of lymphoid infiltrates and aggregates were quantified. CCT absorption was observed in the mucosae of the upper concha and septum provided that aggregates were present, being proportional to aggregate volume. No relationship was noted with isolated scattered lymphoid cells and infiltrates. Passive permeability was unaffected by lymphoid tissue. On this basis, the antigen sampling hypothesis seems to be at least partially substantiated.