Circulating IgA producing cells in the differential diagnosis of Henoch-Schönlein purpura

The number of immunoglobulin producing cells was determined by a plaque forming cell assay in 23 patients with definite Henoch-Schönlein purpura, in 5 children with probable Henoch-Schönlein purpura, in 11 patients with leukocytoclastic vasculitis not associated with a collagen vascular disease, and in 2 age matched control groups of healthy individuals. In the group with leukocytoclastic vasculitis, the numbers of circulating Ig producing cells were within normal limits, and lower than those found in definite Henoch-Schönlein purpura for IgA secreting cells (t = 8.26, p less than 0.001) and IgM secreting cells (t = 2.78, p less than 0.01). The number of circulating IgA secreting cells discriminated between definite Henoch-Schönlein purpura and leukocytoclastic vasculitis with a diagnostic sensitivity of 95.7% and specificity of 90.9%. Four of the 5 patients with probable Henoch-Schönlein purpura also had an increased number of IgA secreting cells. Therefore, an increased number of circulating IgA secreting cells in a patient with hypersensitivity vasculitis without a collagen vascular disease supports the diagnosis of Henoch-Schönlein purpura.