Characterization of B cells in muscle-specific kinase antibody myasthenia gravis.
OBJECTIVE
To characterize B-cell subsets in patients with muscle-specific tyrosine kinase (MuSK) myasthenia gravis (MG).


METHODS
In accordance with Human Immunology Project Consortium guidelines, we performed polychromatic flow cytometry and ELISA assays in peripheral blood samples from 18 patients with MuSK MG and 9 healthy controls. To complement a B-cell phenotype assay that evaluated maturational subsets, we measured B10 cell percentages, plasma B cell-activating factor (BAFF) levels, and MuSK antibody titers. Immunologic variables were compared with healthy controls and clinical outcome measures.


RESULTS
As expected, patients treated with rituximab had high percentages of transitional B cells and plasmablasts and thus were excluded from subsequent analysis. The remaining patients with MuSK MG and controls had similar percentages of total B cells and naïve, memory, isotype-switched, plasmablast, and transitional B-cell subsets. However, patients with MuSK MG had higher BAFF levels and lower percentages of B10 cells. In addition, we observed an increase in MuSK antibody levels with more severe disease.


CONCLUSIONS
We found prominent B-cell pathology in the distinct form of MG with MuSK autoantibodies. Increased BAFF levels have been described in other autoimmune diseases, including acetylcholine receptor antibody-positive MG. This finding suggests a role for BAFF in the survival of B cells in MuSK MG, which has important therapeutic implications. B10 cells, a recently described rare regulatory B-cell subset that potently blocks Th1 and Th17 responses, were reduced, which suggests a potential mechanism for the breakdown in immune tolerance in patients with MuSK MG.
Neuromuscular Division (J.T.G., D.B.S., A.C.G., V.C.J., J.M.M.), Department of Neurology, and Division of Surgical Sciences (J.S.Y., K.J.W.), Department of Surgery, Duke University Medical Center, Durham, NC; Neuromuscular Division (J.F.H.), Department of Neurology, University of North Carolina at Chapel Hill; and Institute of General Pathology (F.S., E.B.) and Department of Neurology (A.E.), Catholic University, Rome, Italy.
Jeffrey T
JT
Guptill
Neuromuscular Division (J.T.G., D.B.S., A.C.G., V.C.J., J.M.M.), Department of Neurology, and Division of Surgical Sciences (J.S.Y., K.J.W.), Department of Surgery, Duke University Medical Center, Durham, NC; Neuromuscular Division (J.F.H.), Department of Neurology, University of North Carolina at Chapel Hill; and Institute of General Pathology (F.S., E.B.) and Department of Neurology (A.E.), Catholic University, Rome, Italy.
John S
JS
Yi
Neuromuscular Division (J.T.G., D.B.S., A.C.G., V.C.J., J.M.M.), Department of Neurology, and Division of Surgical Sciences (J.S.Y., K.J.W.), Department of Surgery, Duke University Medical Center, Durham, NC; Neuromuscular Division (J.F.H.), Department of Neurology, University of North Carolina at Chapel Hill; and Institute of General Pathology (F.S., E.B.) and Department of Neurology (A.E.), Catholic University, Rome, Italy.
Donald B
DB
Sanders
Neuromuscular Division (J.T.G., D.B.S., A.C.G., V.C.J., J.M.M.), Department of Neurology, and Division of Surgical Sciences (J.S.Y., K.J.W.), Department of Surgery, Duke University Medical Center, Durham, NC; Neuromuscular Division (J.F.H.), Department of Neurology, University of North Carolina at Chapel Hill; and Institute of General Pathology (F.S., E.B.) and Department of Neurology (A.E.), Catholic University, Rome, Italy.
Amanda C
AC
Guidon
Neuromuscular Division (J.T.G., D.B.S., A.C.G., V.C.J., J.M.M.), Department of Neurology, and Division of Surgical Sciences (J.S.Y., K.J.W.), Department of Surgery, Duke University Medical Center, Durham, NC; Neuromuscular Division (J.F.H.), Department of Neurology, University of North Carolina at Chapel Hill; and Institute of General Pathology (F.S., E.B.) and Department of Neurology (A.E.), Catholic University, Rome, Italy.
Vern C
VC
Juel
Neuromuscular Division (J.T.G., D.B.S., A.C.G., V.C.J., J.M.M.), Department of Neurology, and Division of Surgical Sciences (J.S.Y., K.J.W.), Department of Surgery, Duke University Medical Center, Durham, NC; Neuromuscular Division (J.F.H.), Department of Neurology, University of North Carolina at Chapel Hill; and Institute of General Pathology (F.S., E.B.) and Department of Neurology (A.E.), Catholic University, Rome, Italy.
Janice M
JM
Massey
Neuromuscular Division (J.T.G., D.B.S., A.C.G., V.C.J., J.M.M.), Department of Neurology, and Division of Surgical Sciences (J.S.Y., K.J.W.), Department of Surgery, Duke University Medical Center, Durham, NC; Neuromuscular Division (J.F.H.), Department of Neurology, University of North Carolina at Chapel Hill; and Institute of General Pathology (F.S., E.B.) and Department of Neurology (A.E.), Catholic University, Rome, Italy.
James F
JF
Howard
Neuromuscular Division (J.T.G., D.B.S., A.C.G., V.C.J., J.M.M.), Department of Neurology, and Division of Surgical Sciences (J.S.Y., K.J.W.), Department of Surgery, Duke University Medical Center, Durham, NC; Neuromuscular Division (J.F.H.), Department of Neurology, University of North Carolina at Chapel Hill; and Institute of General Pathology (F.S., E.B.) and Department of Neurology (A.E.), Catholic University, Rome, Italy.
Flavia
F
Scuderi
Neuromuscular Division (J.T.G., D.B.S., A.C.G., V.C.J., J.M.M.), Department of Neurology, and Division of Surgical Sciences (J.S.Y., K.J.W.), Department of Surgery, Duke University Medical Center, Durham, NC; Neuromuscular Division (J.F.H.), Department of Neurology, University of North Carolina at Chapel Hill; and Institute of General Pathology (F.S., E.B.) and Department of Neurology (A.E.), Catholic University, Rome, Italy.
Emanuela
E
Bartoccioni
Neuromuscular Division (J.T.G., D.B.S., A.C.G., V.C.J., J.M.M.), Department of Neurology, and Division of Surgical Sciences (J.S.Y., K.J.W.), Department of Surgery, Duke University Medical Center, Durham, NC; Neuromuscular Division (J.F.H.), Department of Neurology, University of North Carolina at Chapel Hill; and Institute of General Pathology (F.S., E.B.) and Department of Neurology (A.E.), Catholic University, Rome, Italy.
Amelia
A
Evoli
Neuromuscular Division (J.T.G., D.B.S., A.C.G., V.C.J., J.M.M.), Department of Neurology, and Division of Surgical Sciences (J.S.Y., K.J.W.), Department of Surgery, Duke University Medical Center, Durham, NC; Neuromuscular Division (J.F.H.), Department of Neurology, University of North Carolina at Chapel Hill; and Institute of General Pathology (F.S., E.B.) and Department of Neurology (A.E.), Catholic University, Rome, Italy.
Kent J
KJ
Weinhold