Secretory defense system (SDS) in health and disease

The secretory defense system (SDS) provides antimicrobial activity to mucous surfaces. Tears were used as the representative secretion of the SDS because of a high protein content and ease in obtaining reproducible samples. Tears were obtained with crying or after stimulation with salt; serum was also obtained. The components of the SDS were evaluated in 25 normals, 9 newborns, and 25 patients with increased susceptibility to infection and included assay for: 1) immunoglobulins, 2) protein, 3) isoagglutinins (anti-A, anti-B), 4) lysozyme and 5) complement (C). In normal adults, mean IgG level was 17 mg%, IgA 11 mg%, IgM and C absent, total Ig 28 ± 7 mg%. Mean protein was 11.8 mg/ml, lysozyme 2.0 mg/ml, isoagglutinin titers 1:8. Tear IgG was correlated with serum IgG; tear IgA was not correlated with serum IgA. SDS abnormalities were noted in newborns, in patients with serum antibody deficiencies, and in 4 patients with increased susceptibility to infection and normal serum immunoglobulins. Newborn tears are low in protein, IgA, isoagglutinins, and lysozyme (mean .62 mg/ml) but have normal IgG. Other patients with SDS abnormalities had low total Ig in the tears (<15.0 mg/100 ml), low isoagglutinins, or normal or elevated tear IgM; lysozyme was normal. We conclude that: a) newborns have an SDS deficiency with low lysozyme, b) transport of serum IgG to tears may occur, and c) low tear immunoglobulins, absent tear isoagglutinins or the presence of tear IgM indicate SDS abnormality.