Detection and characterization of plasma cells in peripheral blood: Correlation of IgE⁺ plasma cell frequency with IgE serum titre

In atopic patients and patients with hyper-IgE syndrome (HIE) highly elevated IgE serum levels can be detected. Due to their very low frequency little is known about IgE-producing plasma cells (PC) in peripheral blood. We used CD138 MACS microbeads to enrich plasma cells from peripheral blood of normal donors, atopic patients and one HIE patient. CD138⁺ cells were mainly CD45⁺, CD44⁺⁺, CD19^dim, CD38⁺⁺, CD27⁺⁺, CD86⁺, HLA-DR^+/++, CD71^dim, VLA-4⁺, VLA-5^-, CD28^-, CD25^-, CD69^-, CLA^-, CD20^-, CD21^- and CD22^-. They show weak expression of surface Ig but high levels of intracellular Ig and they secrete Ig in culture. Thus CD138⁺ cells from peripheral blood show characteristics of early plasma cells. IgE⁺ CD138⁺ plasma cells could be detected in 19 of 24 normal donors with an average frequency of 0.06% IgE⁺ cells among CD138⁺ cells. Higher frequencies were detected in atopic patients, atopic patients with markedly elevated serum IgE levels and the hyper-IgE patient with an average of 0.32%, 7.21% and 6.54%, respectively. Additionally, using the recently developed cellular affinity matrix technology, we were able to detect IgE secreting plasma cells and thereby could demonstrate that most of the IgE secreting cells express CD138. The frequency of IgE⁺ CD138⁺ cells among PBMC correlated highly significantly with serum IgE titres (r = 0.8532***), indicating that IgE secreting CD138⁺ cells in peripheral blood are directly related to the plasma cell pool contributing to the IgE titre.