Mpj. Debagues et al., PROTECTIVE IMMUNITY TO BRUCELLA-OVIS IN BALB C MICE FOLLOWING RECOVERY FROM PRIMARY INFECTION OR IMMUNIZATION WITH SUBCELLULAR VACCINES/, Infection and immunity, 62(2), 1994, pp. 632-638
Experiments were performed with BALB/c mice to elucidate the roles of
humoral and cell-mediated immune responses in the acquisition of prote
ctive immunity to Brucella ovis and to compare infection immunity with
immunity developed through vaccination with a hot saline extract (HS)
of B. ovis. Mice convalescing from a primary infection with B. ovis d
isplayed a high level of resistance to reinfection, as evidenced by sp
lenic bacterial counts decreased over 10,000-fold from control groups
at 2 weeks after challenge. Passive transfer assays revealed that prot
ection was mediated by both T lymphocytes and antibodies but that anti
bodies had a substantially gl eater role on the basis of log units of
protection that were transferred. Antibodies specific for HS proteins
in sera from convalescent mice were predominantly of the immunoglobuli
n G 2a and 3 isotypes. Vaccination with HS conferred good protection a
gainst B. ovis, but protection was greatly enhanced by the incorporati
on of QS-21 or other adjuvants. Protection provided by the HS vaccine
resulted largely from immune responses to its protein moieties. A crit
ical evaluation of the protective efficacy of the rough lipopolysaccha
ride component of HS was precluded by its poor immunogenicity in BALB/
c mice. HS-QS-21 afforded protection against challenge infection with
B. ovis as good as that which developed after a primary infection and
as good as or better than that provided by attenuated Brucella meliten
sis vaccine strain Rev 1. Passive transfer experiments confirmed that
the magnitudes of both humoral and cell-mediated forms of protective i
mmunity were equivalent in mice vaccinated with HS-QS-21 and those rec
overing from a primary infection. Protective immunity to B. ovis in mi
ce therefore resembled that to Brucella abortus, except that the relat
ive roles of humoral and cell-mediated immunity, rather than being equ
ivalent, were shifted toward a greater role for antibodies.