Regulation of lymphocyte activation and death

Sammanfattning: T lymohocytes (T cells) and B lymphocytes (B cells) are important effector cells of the adaptive immune system. In response to infections, B cells are activated and produce antibodies against specific antigens. There are two types of T cells, cytotoxic T cells that kill cells infected with bacteria or viruses, and helper T (Th) cells that help B cells produce antibodies by secreting cytokines as well as by upregulating cell surface molecules. In one part of this study, we investigated the expression of one of these cell surface molecules, the CD40 ligand (CD40L), on activated Th cells. We were able to demonstrate the involvement of a new transcription factor, Egr, in regulation of CD40L expression. In the other part of the study we investigated the effects of a group of compounds, N-substituted benzamides, on signaling pathways and transcription factors involved in T and B cell activation and also in apoptosis. We were able to show that N-substituted benzamides having an extra acetyl group (Na-PA and Na-3-CPA) could inhibit activity of the transcription factors NF-kB and NFAT as well as expression of the CD40L in T cells. Activity of the transcription factor AP-1, as well as transcription of IL-2, was on the other hand increased. We could further show that Na-3-CPA inhibited NF-kB activity in pre-B cells. On the other hand, an N-substituted benzamide lacking the acetyl group but containing an extra chloride (3-CPA) was a potent inducer of apoptosis. We could show that 3-CPA induced apoptosis by two mechanisms. Addition of 3-CPA to pre-B cells induced cytochrome c release from the mitochondria and a subsequent activation of caspase-9. 3-CPA could also induce apoptosis in combination with LPS by inhibition of the NF-kB rescue pathway. Thus, we have in this study defined some of the working mechanisms for N-substituted benzamides in T and B cells at a molecular level.