Analysis of the expression of RP105 on peripheral blood B cells

Y Kikuchia, S Koaradaa, Y Tadaa, O Ushiyamaa, F Moritoa, N Suzukia, A Ohtab, T Horiuchid, K Miyakec, K Nagasawaa

a: Department of Internal Medicine, Saga Medical School, 5-1-1 Nabeshima, Saga 849-8501, Japan,
b: Department of Nursing, Saga Medical School,
c: Department of Immunology, Saga Medical School,
d: First Department of Internal Medicine, Faculty of Medicine, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan

Correspondence to: Dr Kikuchi kikuchi@post.saga-med.ac.jp Accepted for publication 3 May 2001

BACKGROUND:   It has previously been shown that RP105, a new B cell surface protein, is lost in activated human B cells.

OBJECTIVE:   To investigate whether there is a difference in B cell activation between patients with dermatomyositis (DM) and those with polymyositis (PM) using RP105 as a marker.

METHODS:   The population of RP105 negative B cells (activated B cells) in the peripheral blood mononuclear cells of seven patients with dermatomyositis (DM) and 11 with polymyositis (PM) was analysed by flow cytometry.

RESULTS:   The percentage of RP105 negative B cells in the peripheral blood of patients with PM was low (5.8 (SD 2.4)%), similar to that of normal subjects. In contrast, all patients with DM showed increased RP105 negative B cell populations (33.0 (6.9)%). Bronchoalveolar lavage fluid from a patient with DM and active interstitial pneumonitis contained a large number of RP105 negative B cells.

CONCLUSION: These findings suggest that the expansion of RP105 negative B cells is a hallmark of DM, and that B cell activation in DM may be pathogenetically different from that in PM.