Quantification of plasma cells in labial salivary glands: increased expression of IgM in Sjögren's syndrome.

Plasma cells expressing IgG, IgA and IgM were quantified in labial salivary glands from patients with Sjögren's syndrome (SS) and compared with glands showing non-specific inflammatory changes and normal controls. In all glands the predominant isotype was IgA but in SS there was a significant increase in both the number and proportions of IgG and IgM positive cells (P less than 0.002). In particular, all SS cases contained greater than 10% IgM positive cells (mean = 26.8 +/- 15.5). The results suggest that accumulation of IgM positive plasma cells may be a specific finding in SS and support the concept that the glandular lesions may be a site of B-cell clonal expansion. Since most B-cell hyperproliferative states in SS, including lymphoma, are associated with synthesis of IgM simple quantification of plasma cells may have important diagnostic and prognostic significance.