Effects of nuclear factor-κB on regulation of cytokine expression and apoptosis in bovine monocytes exposed to Mycobacterium avium subsp paratuberculosis

Abstract

To evaluate the role of the nuclear factor-kappaB (NF-kappaB) in the response of bovine monocytes to exposure to Mycobacterium avium subsp paratuberculosis (MAP). Monocytes from healthy adult Holstein cows that were known to be negative for MAP infection. Monocytes were incubated with MAP organisms with or without a specific inhibitor of the NF-kappaB pathway (pyrrolidine dithiocarbamate), and activation of the NF-kappaB pathway was detected by use of an electrophorectic mobility shift assay. The capacities of monocytes to express tumor necrosis factor (TNF)-alpha, interleukin (IL)-10, and IL-12; to acidify phagosomes; to phagocytize and kill MAP organisms; and to undergo apoptosis were evaluated. Addition of MAP organisms to monocytes activated the NF-kappaB pathway as indicated by increased NF-kappaB-DNA binding. Addition of pyrrolidine dithiocarbamate prevented nuclear translocation of NF-kappaB, decreased expression of TNF-alpha and IL-10, and increased IL-12 expression. Treatment of MAP-exposed monocytes with pyrrolidine dithiocarbamate increased the rate of apoptosis but failed to alter phagosome acidification, organism uptake, or organism killing by those cells. Results indicated that NF-kappaB rapidly translocated to the nucleus after exposure of bovine monocytes to MAP organisms. These data suggest that NF-kappaB is involved in initiation of inflammatory cytokine transcription and inhibition of apoptosis but that it is not directly involved in phagosome acidification or organism killing.