Local immunity in Newcastle disease: some recent experiments.
Following primary exposure by the ocular route to lentogenic Newcastle disease virus (NDV) the lacrymal fluid, saliva and tracheal washes of three-week old specific pathogen free chickens acquired specific virus-neutralizing activity which considerably exceeded transudation of circulating antibody. All three secretions contain IgA which, at least in saliva, accounted for 85% of its activity, the remanider being due to IgG. Antibody in secretions limited, but did not prevent, reinfection of the trachea when birds were challenged two weeks later. In contrast to an elevation of circulating antibody titre, challenge induced only a repeated primary response in secreted antibody. Ocular infection induced marked lymphoid and plasma cell activity in the Harderian gland which is a major source of specific antibody in lachrymal and possibly other fluids. Functional ablation of the gland can be effected by occlusion of its draining duct, providing a means for evaluation of its immunological significance.