Role of typhoid antigens in protection and pathogenicity for mice.

Swiss white mice immunized with acetone-killed vaccines prepared from strains of Salmonella typhosa, S. typhimurium, and mouse-virulent S. typhimurium hybrids which had acquired, by conjugal genetic transfer, the S. typhosa antigens 9, Vi, and d were challenged with the S. typhimurium hybrids and with the S. typhimurium parent strain. The results of these experiments suggested that the Salmonella somatic antigens were important in conferring protection against death in this system. The S. typhosa Vi antigen did not appear to play any significant role in this protection. The S. typhimurium hybrids employed in these studies did not show any loss of mouse virulence as the consequence of acquisition of various combinations of the S. typhosa somatic, flagella, or Vi antigens, nor did S. typhosa hybrids which had acquired the somatic antigen of S. typhimurium show any increase in mouse virulence.