For the most part, decline in human immune function in advance age is due to decrease in T cell responses. The specific focus of this project is on determining the molecular and cellular alterations that lead to decreased in vitro proliferation of T cells from older subjects to mitogenic lectin and antibodies. Most of this decrease is due to diminished induction of synthesis of gene products that are required for entry into the cell cycle during the prereplicative interval, but early cytoplasmic intermediates that activate these genes are induced to the same level in young and old T cells. The hypothesis is that decreased expression of mitogen activated gene products is due to a specific defect in events at the nuclear level required for expression of newly synthesized gene products.
The Aims are: 1) To determine by Northern Blot analysis and other methods that reduced abundance of mRNA for mitogen activated gene products is responsible for diminished synthesis of these proteins in old T cells. The gene product analyzed will include Il-2 and the IL-2 receptor, and two proteins, HSP90 and p73, that are also part of the heat-shock response in lymphocytes. Induction of mRNA for HSP90 and p73 after heat-shock will be compared to induction following mitogen activation. 2) To determine the mechanisms responsible for reduced mRNA induction after heat-shock and mitogen activation. Transcriptional activation of specific genes will be determined by nuclear """"""""run-off"""""""" assays and mRNA half-life determined. The major test that aging affects mRNA processing in the nucleus will involve inhibition of mRNA splicing by severe heat-shock. 3) To determine the effect of aging on transport of proteins required for activation of DNA replication. Extracts from proliferating cells induce transport of high molecular weight proteins into quiescent nuclei leading to activation of DNA replication. The DNA replication response in lymphocyte nuclei isolated from older subjects is decreased and it will be determined if this is due to a defect in protein transport through the nuclear envelope.
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