Previous analyses of V gene use have provided indirect evidence that SG MNHL may frequently express RF. We demonstrate that this hypothesis is true in the 2 patients we studied. Large-scale studies will be needed to establish the exact frequency of RF specificity among SS-associated MNHL.

B cells play a central role in systemic lupus erythematosus (SLE) pathophysiology but dysregulated pathways leading to a break in B cell tolerance remain unclear. Since Toll-like receptor 9 (TLR9) favors the elimination of autoreactive B cells in the periphery, we assessed TLR9 function in SLE by analyzing the responses of B cells and plasmacytoid dendritic cells (pDCs) isolated from healthy donors and patients after stimulation with CpG, a TLR9 agonist. We found that SLE B cells from patients without hydroxychloroquine treatment displayed defective in vitro TLR9 responses, as illustrated by the impaired upregulation of B cell activation molecules and the diminished production of various cytokines including antiinflammatory IL-10. In agreement with CD19 controlling TLR9 responses in B cells, decreased expression of the CD19/CD21 complex on SLE B cells was detected as early as the transitional B cell stage. In contrast, TLR7 function was preserved in SLE B cells, whereas pDCs from SLE patients properly responded to TLR9 stimulation, thereby revealing that impaired TLR9 function in SLE was restricted to B cells. We conclude that abnormal CD19 expression and TLR9 tolerogenic function in SLE B cells may contribute to the break of B cell tolerance in these patients.

The mechanism underlying the prothrombotic state that characterizes the primary antiphospholipid syndrome proves to be difficult to define mainly because of the variety of the phospholipid and protein targets of antiphospholipid antibodies that have been described. Much of the debate is related to the use of polyclonal antibodies during the different antiphospholipid assays. To better describe the antiphospholipid antibodies, a strategy was designed to analyze the reactivity of each one antibody making up the polyclonal anticardiolipin activity, breaking down this reactivity at the clonal level. This was performed in a single patient with primary antiphospholipid syndrome by combining (1) the antigen-specific selection of single cells sorted by flow cytometry using structurally bilayered labeled anionic phospholipids and (2) IntroductionAntiphospholipid autoantibodies (aPLs) 1 are associated with thrombosis, recurrent fetal loss, and thrombocytopenia in patients with antiphospholipid syndrome (APS). [2][3][4] The mechanism of the characteristic prothrombotic state related to aPLs during APS is still under debate. 5 Much of it is related to the definition of the precise nature of aPL specificity, which remains unclear because of the number of possible antigenic targets discovered over the last few years. It is now accepted that plasma proteins play an important role in aPL reactivity. 6,7 The most common protein cofactors are ␤2GP1 8,9 and prothrombin. [10][11][12] Other phospholipid (PL)-binding proteins such as protein C9, protein S9, and annexin V 13 have also been found to have cofactor properties. On one hand, studies have shown that the binding of aPLs to cardiolipin (CL) is enhanced by the addition of one cofactor (␤2GP1, prothombin, protein C, protein S), which suggests that aPLs react to a complex compounded of anionic PLs and a cofactor 8,10,11 or to an epitope that becomes exposed when a protein is bound to a PL. [14][15][16] On the other hand, other studies have shown that aPLs are able to bind directly to immobilized ␤2GP1 [17][18][19] or PT 20,21 in the absence of PL. In addition, some studies have shown that anti-␤2GP1 antibodies (Abs) are primarily associated with thrombosis in APS 22-24 although other reports have involved others Abs as anti-PT 25 or lupus anticoagulant. 26 It appears that most of these difficulties are related to the use of polyclonal Abs (serum or purified immunoglobulin [Ig]) 7,8,10,11 or a few monoclonal IgM 15,27-29 or IgG 30-33 aPLs originating from different patients. We therefore considered it necessary to concentrate our attention on aPL reactivity of each Ab making up the polyclonal aPL reactivity, breaking down this reactivity at the clonal level in a single patient.The major methods currently in use for the production of human monoclonal antibodies (mAbs) are Epstein-Barr virus transformation, 34 mouse-human hybridomas, 35 or human-human hybridomas 36 and fusion of Epstein-Barr virus-transformed B lymphocytes with a malignant cell line. 37 These methods have their dr...