Common enterobacterial antigen. II. Effect of immunization on challenge with heterologous bacilli.

Studies were carried out evaluating the protective activity of immunization with common enterobacterial antigen (CA) against challenge with heterologous gram-negative bacilli. Active immunization of mice with Escherichia coli 0:14 elicited titers of antibody to CA of 1:640 or greater but completely failed to enhance resistance to challenge by mouse virulent strains of Klebsiella pneumoniae or E. coli. Similarly, two lots, 324 and 422, of rabbit antisera to CA failed to afford passive protection to mice challenged with K. pneumoniae or E. coli. A third lot, 166, of rabbit antisera to CA did passively protect mice. The protective activity of antisera 166 was demonstrated to reflect its content of antibody to another cross-reactive antigen, Re determinant, of gram-negative bacilli which has previously been shown to protect against infections with heterologous bacilli rather than any protective effect of antibody to CA. These studies failed to demonstrate any protective activity of antibody to CA against challenge with heterologous CA containing gram-negative bacilli.