Proliferative Response and Cytokine Production of Bovine Peripheral Blood Mononuclear Cells Induced by the Superantigens Staphylococcal Enterotoxins and Toxic Shock Syndrome Toxin-1

Abstract

The potential of staphylococcal enterotoxin A(SEA), B(SEB), C(SEC) and toxic shock syndrome toxin-1 (TSST-1) to act as superantigens by inducing polyclonal T-cell mitogenesis and cytokine production was tested on bovine peripheral blood mononuclear cells (PBMC). These four toxins were capable of inducing strong proliferative response of PBMC from calves over a broad dosage range (1 pg/ml to 1 μg/ml) in vitro. The toxin-activated blast cells consisted of both CD4⁺ T-cells and CD8⁺ T-cells, but the T-cell proliferation depended upon the presence of monocytes. Treatment of monocytes with monoclonal antibody to major histocompatibility complex class II antigens substantially inhibited the toxin-induced T-cell proliferative response, but paraformaldehyde-fixation did not abrogate the accessory function. SEA, SEB, SEC and TSST-1, all induced the in vitro release of interleukin-2, interferon γ and tumor necrosis factor α in a dose dependent manner. The results indicate that SEA, SEB, SEC and TSST-1 are capable of acting as superantigens by stimulating bovine T-cells as shown in the human and murine systems. The possible implications of these toxins in the immunopathogenesis of bovine mastitis caused by the infection with staphylococcus aureus are discussed.