IN-VITRO STUDIES WITH LYMPHOCYTES FROM SHEEP ORALLY INOCULATED WITH AN AROMATIC-DEPENDENT MUTANT OF SALMONELLA-TYPHIMURIUM

It was previously shown that a live aroA-strain of Salmonella typhimur ium of ovine origin was a safe and effective vaccine against salmonell osis in sheep. The protective effect was observed in the apparent abse nce of a detectable, systemic T cell response. In the present study, p opulations of B and T cells from the peripheral blood of sheep vaccina ted with S25/1aroA were separated and their responsiveness in vitro to Salmonella was examined. The purified T cells proliferated very weakl y in response to Salmonella in the absence of interferon-gamma and int erleukin 2/4 production. However, whole peripheral blood mononuclear c ells and purified B cells proliferated strongly in response to Salmone lla, and Salmonella-specific IgM antibodies could be detected in cell supernatants. Furthermore, Salmonella-specific IgM-producing cells wer e detected at low frequency by enzyme linked immunospot techniques. Th ese observations extend the earlier findings that oral vaccination wit h S25/1aroA primes predominantly antigen-specific B cells in the absen ce of strong Salmonella-specific T cell responses.