Studies on the origin and composition of IgA in rat tears

Experiments were carried out to quantify the proportion of IgA in rat tears that arrives from the circulating IgA pool in the blood, as opposed to that supplied by local synthesis in the lacrymal gland. Rats were injected subcutaneously with an IgA-secreting rat hybridoma cell line (91c), which was allowed to grow in vivo, in order to raise the levels of plasma IgA of known antibody specificity. In rats where serum 91c IgA concentrations had built up to 0.3 mg/ml or more, unstimulated tears contained 91c antibody activity of a molecular weight range that corresponded to that of the polymeric sizes of IgA, and was associated with secretory component. The concentrations of IgA in tear samples were about 0.3% of those in matched serum samples. Thus, a plasma contribution is made to the IgA in tears, but greater than 99% of the tear IgA is synthesized locally in the lachrymal gland.