Vbeta-dependent stimulation of bovine and human T cells by host-specific staphylococcal enterotoxins

Staphylococcus aureus isolates from bovine and ovine species produce unique molecular variants of type C staphylococcal enterotoxin (SEC). The SEC animal variants have greater than 98% amino acid sequence identity with SEC1, a human-associated SEC. The two SEC animal variants have been designated SEC(bovine) and SEC(ovine) according to their corresponding host species. We showed previously that these toxins induce quantitatively different levels of T-cell stimulation in several animal species. The present study compared the abilities of these closely related host-specific SEC variants to stimulate Vbeta-bearing T cells from bovine and human donors. All three toxins expanded human T cells bearing T-cell receptor Vbeta elements (huVbeta) 3, 12, 13.2, 14, 15, 17, and 20. However, SEC1 resulted in greater expansion of hyVbeta12 than either SEC(bovine) or SEC(ovine). In addition, bovine T cells proliferate in a Vbeta-dependent manner in response to these superantigens (SAgs). All three toxins induced the proliferation of bovine T cells bearing the previously sequenced Vbeta element (boVbeta) from the bovine T-cell clone BTB13 (boVbetaBTB13). SEC1 and SEC(ovine) also were able to induce proliferation of bovine T cells bearing boVbetaBTB35, which SEC(bovine) failed to stimulate. The species-specific differences in T-cell proliferation exhibited by these closely related SEC variants may reflect the evolutionary adaptation of S. aureus, presumably to increase its host range by the manipulation of the immune system in a host-specific manner.