Different toxoplasma
antigens were entrapped within
liposomes and evaluated, in this form, for their ability to protect Swiss mice against toxoplasma
infection: soluble tachyzoite
antigen (L/TAg), tissue
cyst (L/CAg), tachyzoite plus tissue
cyst (L/TCAg) or purified
antigen of tachyzoite (L/pTAg). The
protein used in L/pTAg was purified from tachyzoites using a stage-specific
monoclonal antibody which reacted at a molecular weight of 32 kD in SDS PAGE and
silver stain using reduced condition. To compare the immuno-adjuvant action of
liposomes and of Freund's Complete Adjuvant (FCA), another group of mice was immunized with soluble tachyzoite
antigen (STAg) emulsified in FCA (FCA/TAg). Control groups were inoculated with (STAg) alone,
phosphate-buffered saline (PBS), FCA with PBS (FCA/PBS) and empty
liposomes (L/PBS). Mice were inoculated subcutaneously with these
antigens six, four and two weeks before a challenge with 80 tissue
cysts of the P strain of Toxoplasma gondii orally. All mice immunized with or without adjuvant showed a humoral response, as measured by Elisa. However, no correlation was found between antibody titer and protection against the challenge. All mice immunized with L/pTAg or L/TCAg survived (100), whereas 80% and 90% of mice from groups which received respectively PBS or FCA/PBS and L/PBS died. All mice immunized with
antigens entrapped within
liposomes (L/TAg, L/CAg, L/TCAg and L/pTAg) showed low numbers of intracerebral
cysts.