The experiments for each sample were repeated at least three times and bars represent the mean and standard deviation of three separate experiments. PBMCs from 48 SLE patients, 32 patients with rheumatoid arthritis(RA) and 24 healthy individuals were analyzed for the expression and activation of PYK2 by western-blotting and immunocytochemistry. The other isolated PBMCs from patients with this condition were Ro 28-1675 cultured and stimulated with PMA or TyrA9, and then the expression of costimulatory molecules CD40L and CTLA4 was evaluated using flow cytometry, PBMCs proliferation was determined with [3H]-thymidine incorporation (CPM). == Results == Compared with RA patients and healthy donors, PBMCs from SLE patients expressed more of both the total PYK2 protein and its activated/phosphorylated form. The increase of activated PYK2 protein in SLE PBMCs was correlated with the complication of nephritis and inversly associated the level of serum complements. In active SLE patients, activation of PYK2 in PBMCs is accompanying the increased Ro 28-1675 cell proliferation and the induced expression of costimulatory molecules CD40L and CTLA4. == Conclusion == Our findings indicate that phosphorylated PYK2 in SLE PBMCs may induce the expression of CD40L and CTLA4, and subsequently the cell proliferation. PYK2 signaling enhances the autoreactive lymphocyte activation and plays an important role in the pathogenesis of SLE. == Background == Systemic lupus erythematosus (SLE) is a representative systemic autoimmune disease characterized by activated T cells and polyclonally activated B cells that produce autoantibodies. Activation of autoreactive T and B cells plays a pivotal role in the pathogenesis of this disease [1,2]. Although SLE T cells have impaired interleukin-2 (IL-2) production and proliferative response to stimulation of the T cell receptor-CD3 compound[3,4], expression of costimulatory molecules such as CD40L and CTLA4, which is essential for lymphocyte activation [5,6], is up-regulated [7-10]. These molecules are thus targets in considering effective strategies in the treatment of SLE. Lupus mice treated with antibody against CD40L or CTLA4-Ig have lower level of anti-doublestranded DNA antibodies, later development of nephritis, and prolonged survival time [11-13]. In patients with SLE, the reduced expression of CD28 costimulatory molecule on both CD4- and CD8-T cells is also well documented [14,15]. CD28-mediated costimulatory activity, following the interaction of T cells with B cells, is significantly decreased in patients with SLE [14]. Thus, it seems that costimulatory signals in SLE T cells may differ from those present in normal T cells. Lately, in SLE T cells, focal adhesion kinase (FAK) have been shown to be involved in costimulatory molecule expression and cell proliferation[16]. Similar Ro 28-1675 findings regarding the involvement of FAK were also reported in other inflammation-related diseases, such as rheumatoid arthrithis (RA)[17,18], diabetes[19], chronic inflammatory bowel diseases[20] and asthma[21]. It is thus likely that FAK may represent a new molecular target for the anti-inflammatory treatment. The proline-rich tyrosine kinase 2 (PYK2) is Ro 28-1675 a nonreceptor protein tyrosine kinase that is structurally related to FAK [22]. It is also known as cell adhesion kinase- or related adhesion focal tyrosine kinase. Unlike the ubiquitous expression of prototype FAK, PYK2 is primarily expressed in populations of neuronal and hematopoetic cells[23]. PYK2 becomes activated in response to stimulation through a number of receptors, of which include integrins[24,25], cytokine receptors [26-28] and lymphocyte antigen receptors [29-31]. Numerous studies over the years have shown that PYK2 provides important signals during the activation of lymphocytes [32-35]. However, in SLE, PYK2’s Ro 28-1675 expression and activation in PBMCs, as well as the functional significance of PYK2 in T cell and B cell activation, remains unclear. In this study, we showed that PYK2 is significantly increased and activated in PBMCs of patients with active SLE. In addition, we showed the involvement of PYK2 proteins in the up-regulation of CD40L and CTLA4 expression and PBMCs proliferation. == Methods == The study protocol was approved by the Human Ethics Review Committee of Shandong Provincial Hospital, Jinan, China. A signed consent form Rabbit polyclonal to GRB14 was obtained from each subject prior to study participation. == Subjects == The study subjects were 24 healthy volunteers, 32 RA patients (6 men and 26 women, mean age 42.3 years [range 21-67 years]), and 48 SLE patients (7 men and 41 women, mean age 33.9 years [range 11-69 years]), of whom 12 had inactive SLE disease and 36 had active SLE disease at the time of the study. All patients fulfilled the diagnostic criteria of the American College of Rheumatology for the classification of SLE or RA [36,37]. All SLE patients were admitted to our department between 2006 and 2009, and SLE disease activity was evaluated by the SLE Disease Activity Index (SLEDAI) score[38]..