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The research described herein evaluates the expression and functional significance of peroxisome proliferator activator receptor-γ (PPAR-γ) on B-lineage cells. Normal mouse B cells and a variety of B lymphoma cells reflective of stages of B cell differentiation (e.g., 70Z/3, CH31, WEHI-231, CH12, and J558) express PPAR-γ mRNA and, by Western blot analysis, the 67-kDa PPAR-γ protein. 15-Deoxy-Δ12,14-PGJ2 (15d-PGJ2), a PPAR-γ agonist, has a dose-dependent antiproliferative and cytotoxic effect on normal and malignant B cells as shown by [3H]thymidine and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assays. Only PPAR-γ agonists (thiazolidinediones), and not PPAR-α agonists, mimicked the effect of 15d-PGJ2 on B-lineage cells, indicating that the mechanism by which 15d-PGJ2 negatively affects B-lineage cells involves in part PPAR-γ. The mechanism by which PPAR-γ agonists induce cytotoxicity is via apoptosis, as shown by annexin V staining and as confirmed by DNA fragmentation detected using the TUNEL assay. Interestingly, addition of PGF2α, which was not known to affect lymphocytes, dramatically attenuated the deleterious effects of PPAR-γ agonists on B lymphomas. Surprisingly, 15d-PGJ2 induced a massive increase in nuclear mitogen-activated protein kinase activation, and pretreatment with PGF2α blunted the mitogen-activated protein kinase activation. This is the first study evaluating PPAR-γ expression and its significance on B lymphocytes. PPAR-γ agonists may serve as a counterbalance to the stimulating effects of other PGs, namely PGE2, which promotes B cell differentiation. Finally, the use of PGs, such as 15d-PGJ2, and synthetic PPAR-γ agonists to induce apoptosis in B-lineage cells may lead to the development of novel therapies for fatal B lymphomas.

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CD40 is a 50 kDa transmembrane protein important for regulating B lymphocyte proliferation and differentiation. This novel activation antigen is primarily expressed by hematopoietic cells including B lymphocytes, follicular dendritic cells, and monocytes. Recently, human fibroblasts from.a variety of tissues were shown to display CD40; however, its function was unknown. Cellular responses mediated by CD40 are naturally triggered by its counter‐receptor, the CD40 ligand, which is displayed on activated T cells, mast cells, eosinophils, basophils, and B lineage cells. This study investigated the functional significance of CD40 expression on periodontal fibroblasts, in the context of periodontal inflammation. The experiments reported herein demonstrate constitutive CD40 expression on cultured periodontal ligament (PDL) and gingival fibroblasts. Interestingly, cells of gingival origin displayed up to 13‐fold higher constitutive levels of CD40, versus fibroblasts from PDL. Interferon gamma (IFN‐γ) treatment enhanced CD40 expression on PDL and gingival fibroblasts, with up to 61‐fold induction of expression. Immunohistochemical staining was used to detect CD40 on fibroblastic cells in both normal and acutely inflamed gingival tissue. Expression of CD40 in inflamed tissue was significantly higher than in uninflamed tissue. Western blot analysis of anti‐CD40 triggered cells revealed the induction of tyrosine phosphorylation on a 50 kDa protein in PDL and gingival fibroblasts. These results indicate that CD40 is an active signaling conduit in periodontal fibroblasts. This concept was further substantiated by the fact that CD40 engagement stimulated interleukin 6 (IL‐6) production by gingival fibroblasts, but not periodontal ligament fibroblasts. Overall, these results demonstrate that CD40 on periodontal fibroblasts may functionally interact with CD40L‐expressing cells. This CD40/CD40L interaction can stimulate fibroblast activation and synthesis of the proinflammatory cytokine IL‐6. J Periodontol 1997;68:284–292.

Prostaglandins of the E‐series stimulate B lymphocytes by enhancing immunoglobulin‐class switching and antibody production. Little is known about whether or not other prostaglandins affect B lineage cells and perhaps counterbalance the stimulatory effects of PGE2. PGD2 is a major product of cyclooxygenase in bone marrow and in macrophages, suggesting a role for this lipid product in immunological responses. PGD2 undergoes dehydration to the biologically active prostaglandin 15‐deoxy‐Δ12,14‐PGJ2 (15d‐PGJ2) that binds to the nuclear receptor known as peroxisome proliferator‐activated receptor gamma (PPAR‐γ). We found that normal mouse B cells and a Wvariety of B lymphoma cells (e.g., 70Z/3, WEHI‐231, CH12, and J558) express PPAR‐γmRNA and the 67‐kDa PPAR‐γ protein. 15d‐PGJ2 had a dose‐dependent antiproliferative/cytotoxic effect on normal and malignant B cells, as shown by 3H‐thymidine and MTT assays. Only PPAR‐γ agonists (i.e., thiazolidinediones) mimicked the effect of 15d‐PGJ2 on B lineage cells, indicating that the mechanism by which 15d‐PGJ2 negatively affects B lineage cells involves PPAR‐γ. The mechanism whereby PPAR‐γ agonists induced cytotoxicity is via apoptosis, as shown by Annexin V assays. PPAR‐γ agonists may serve as a counterbalance to the stimulating effects of PGE2, which promotes B‐cell differentiation. The use of prostaglandins, such as 15d‐PGJ2, and synthetic PPAR‐γ agonists to induce apoptosis in B lineage cells may lead to the development of therapies for fatal PGE2‐resistant B lymphomas.

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