Gene expression in antigen-specific CD8(+) T cells during viral infection

Following infection with intracellular pathogens, Ag-specific CD8(+) T cell s become activated and begin to proliferate. As these cells become activate d, they elaborate effector functions including cytokine production and cyto lysis. After the infection has been cleared, the immune system returns to h omeostasis through apoptosis of the majority of the Ag-specific effector ce lls. The surviving memory cells can persist for extended periods and provid e protection against reinfection. Little is known about the changes in gene expression as Ag-specific cells progress through these stages of developme nt, i.e., naive to effector to memory. Using recombinant MHC class I tetram ers, we isolated Ag-specific CD8(+) T cells from mice infected with lymphoc ytic choriomeningitis virus at various time points and performed semiquanti tative RT-PCR, We examined expression of: 1) genes involved in cell cycle c ontrol, 2) effector and regulatory functions, and 3) susceptibility to apop tosis, We found that Ag-specific CD8(+) memory T cells contain high steady- state levels of Bcl-2, Bax, IFN-gamma, and lung Kruppel-like factor (LKLF), and decreased levels of p21 and p27 mRNA. Moreover, the pattern of gene ex pression between naive and memory cells is distinct and suggests that these two cell types control susceptibility to apoptosis through different mecha nisms.