DBA/2 mice immunized with
poly(A).
poly(U) complexed with
methylated bovine serum albumin and emulsified in Freund's complete adjuvant were protected against challenge with Friend
leukemia virus. There was no correlation between the level of antibody to the immunogen in the prechallenge serum and induced resistance to the virus. Although prechallenge sera of mice given the same amount of the duplex in a single inoculum bound 9.7% of
poly(A).poly([(3)H]U) input, as compared to 45.3% bound by the prechallenge sera of mice given the immunogen in divided doses, both groups of mice were equally resistant to
infection. Immunization with two other nonviral agents,
bovine serum albumin fraction V or dinitrophenylated
keyhole limpet hemocyanin, induced the same level of protection. A sparing effect of approximately 10(1.5) in infectivity was afforded the immunized mice. Immunization with either
poly(A).
poly(U) alone or with the carrier
methylated bovine serum albumin was ineffective. In addition to
antibodies to the respective immunogens, the prechallenge sera of the immunized mice also contained antibody to Friend
leukemia virus gp71. The presence of such
viral antibodies was not always related to resistance to
infection by Friend virus. Some immunized mice that survived
infection did not have gp71 antibody in their serum before challenge, and mice immunized with
poly(A).
poly(U) alone were susceptible to
infection, although their prechallenge sera contained antibody to gp71. The mechanism involved in the induction of resistance to
infection is not known. The effect may be mediated through a modification of the expression of both endogenous and exogenous type C viruses and affect immunological mechanisms controlling cellular responses.