The neonatally thymectomized rat: a model for compensatory IgM antibody formation in exocrine secretions.

The effect of T-cell deprivation on IgM antibodies in saliva was studied in rats. IgM was never detected in salivas obtained from normal or sham-thymectomized rats, but was detected in saliva samples from 8/15 (53.3%) rats that had undergone neonatal thymectomy. All (6/6) neonatally thymectomized rats exhibited an IgM antibody response to DNP in salivary secretions after local immunization with a T-dependent antigen (DNPBGG), while no IgA anti-DNP activity was detected in saliva from these antimals. IgM antibodies were detected in saliva from 5/7 thymectomized rats following local injection with a T-independent antigen (DNP-Lys-Gicoll). This was accompanied by detectable but substantially reduced levels of secretory IgA antibody in saliva from 7/7 rats. The results suggested that absent or decreased salivary IgA responses accompanying T-cell deprivation in the rats are compensated for by secretion of IgM antibodies into the saliva. The neonatally thymectomized rat may thus provide a model for the study of synthesis, secretion and protective potential of exocrine IgM antibodies.