ABSTRACT
We have previously shown that jacalin, a CD4+ T cell lectin, induces phosphorylation of intracellular events, moderate levels of interleukin (IL)-2 secretion. We have also shown that in the presence of CD28 costimulation, jacalin induces IL-4 secretion. In the present study, we showed that stimulation of normal CD4+ T cells with jacalin plus CD28 cross-linking (CD28XL) resulted in phosphorylation of signal transducer and activator of transcription (STAT)-6 and expression of Bcl-2 and Bcl-xL, which were inhibited significantly when cells were cultured in the presence of the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580. We further generated jacalin-induced CD4+ T cell blasts, examined the effects of CD28XL, and observed enhanced up-regulation of p38 and activation of STAT-6, Bcl-2, and Bcl-xL. Engagement of CD28 alone induced a marked degree of phosphorylation of p38 MAPK and IL-4 secretion in memory T cells (jacalin blasts), whereas in naïve T cells, jacalin plus CD28XL was required to induce these molecules. Incubation of cells with p38 inhibitor prior to CD28XL resulted in down-modulation of all these molecules. Further treatment with IL-4 has not reversed this trend. Our studies imply that p38 MAPK may play an important role in induction of these molecules and a putative role in protecting cells from undergoing apoptosis.
Subject(s)
CD28 Antigens/physiology , CD4-Positive T-Lymphocytes/drug effects , Interleukin-4/biosynthesis , Plant Lectins/pharmacology , p38 Mitogen-Activated Protein Kinases/physiology , Antibodies, Monoclonal/pharmacology , CD28 Antigens/immunology , CD4-Positive T-Lymphocytes/metabolism , Cells, Cultured/drug effects , Cells, Cultured/metabolism , Genes, bcl-2 , Humans , Imidazoles/pharmacology , Immunologic Memory , Interleukin-4/genetics , Interleukin-4/metabolism , Interleukin-4/pharmacology , Lymphocyte Activation/drug effects , Lymphocyte Activation/physiology , MAP Kinase Signaling System/drug effects , Phosphorylation/drug effects , Protein Processing, Post-Translational/drug effects , Proto-Oncogene Proteins c-bcl-2/biosynthesis , Pyridines/pharmacology , STAT6 Transcription Factor/biosynthesis , STAT6 Transcription Factor/genetics , Th1 Cells/immunology , Th2 Cells/immunology , bcl-2-Associated X Protein/biosynthesis , bcl-2-Associated X Protein/genetics , bcl-X Protein/biosynthesis , bcl-X Protein/genetics , p38 Mitogen-Activated Protein Kinases/antagonists & inhibitors , p38 Mitogen-Activated Protein Kinases/pharmacologyABSTRACT
Costimulatory signals play an important role in the development of T helper cell type 1 (Th1) or Th2 type. Little is known about jacalin plus CD28-mediated signaling and cytokine secretion. In the present study, we analyzed the intracellular signaling events following stimulation of CD4+ T cells with jacalin plus CD28 cross-linking (CD28XL) with anti-CD28 antibody. Our results indicate enhanced phosphorylation of Tec and linker for activation of T cells when compared with stimulation with jacalin alone or CD28XL alone. Stimulation with jacalin or CD28XL appears to be insufficient to induce interleukin (IL)-4 secretion; however, CD28XL followed by stimulation with jacalin resulted in enhanced phosphorylation of p38 mitogen-activated protein kinase (MAPK) and increased secretion of IL-4. However, compared with stimulation with phorbol 12-myristate 13-acetate plus ionomycin, jacalin plus CD28XL resulted in decreased levels of tumor necrosis factor alpha secretion. Addition of p38 inhibitor, SB203580, inhibited p38 phosphorylation and IL-4 secretion. These data suggest that jacalin stimulation alone appears to be insufficient for Th2 development, and addition of CD28 costimulation induced Th2 generation. We propose that jacalin plus CD28XL induces Th2 differentiation via activation of p38 MAPK.
