Experimental Escherichia coli 06 infection in mice. II. Protective factors of immunity after immunosuppression.

The increase of the resistance against intraperitoneal (i.p.) Escherichia coli to infection was studied in immunized mice with or without immunosuppression with cyclophosphamide (Cy), or/and niridazole (Nir). These agents suppress antibody formation and T-cell mediated immunity respectively. An infection system was utilized permitting exclusive study of immunity against the 06 antigen. The antibody titers in serum were recorded with an enzyme-linked immunosorbent assay, ELISA. The following findings were made: (1) One immunization resulted in protection against i.p. E. coli 06 infection as well as in antibody titers measured with the ELISA. Two immunizations given with a 30-day interval increased the noted levels even more. (2) The resistance to infection after one immunization was fully transferable with immune serum; the resistance after two immunizations was not fully transferable with immune serum. (3) Treatment with cyclophosphamide diminished the antibody formation after immunization but not the resistance to infection. The resistance raised by one immunization was transferable by immune serum from immunosuppressed animals; the resistance raised by two immunizations was partly transferable bny such immune. (4) Treatment with niridazole, which inhibits T-cell mediated immunity, did not alone or in combination with cyclophosphamide affect the resistance pattern after immunization.