Synthesis and secretion of secretory immunoglobulins: with special reference to dental diseases

The distribution of immunoglobulin-containing cells in human tonsils, salivary glands, and inflamed gingiva is described. The cellular localization of J chain indicates that this peptide is a basic gene product of B cells that is expressed only in the early phase of clonal differentiation. Gland-associated immunocytes apparently are derived from this phase, which may be relevant to their local homing mechanism. The selective glandular transport of dimeric or polymeric IgA and 19S IgM may be determined by the content of J chain in these immunoglobulins. A J-chain-dependent configuration seems to be responsible for their noncovalent affinity for SC, and this may explain their specific reception at the epithelial cell membranes. Subsequent stabilization of the Ig-SC complexes takes place during their external transport, probably because of disulfide exchange. The latter process is more efficient for secretory IgA than for secretory IgM. The secretory dynamics of parotid IgA differs from that of other parotid proteins and is highly dependent on the degree of secretory stimulation. The secretion rate (mug/min/gland) seems to be a better measure of an individual's parotid IgA output than the absolute concentration of IgA in the secretion. A low parotid IgA secretion rate is associated with high susceptibility to dental caries, perhaps reflecting inferior resistance to dental plaque formation. It is not known whether such resistance, in part, is determined by specific antibodies to certain bacterial antigens. A potential candidate for an efficient preventive action of salivary antibodies could be the GTF enzyme system of S mutans. However, we were able to demonstrate only extremely rare immunocytes producing antibodies to GTF in human tonsils and gingiva, and none at all in salivary glands.