Antibody in host defense against mouse pneumonitis agent (murine Chlamydia trachomatis)

In a murine model of chlamydial pneumonia employing murine Chlamydia trachomatis, immune serum given intranasally delayed death in nude (nu/nu) mice and prevented death in nu/+ mice. Serum-derived immunoglobulin G and A fractions and immune lavage fluid fractions containing immunoglobulins G and A were effective in producing protection when used to opsonize the murine C. trachomatis inoculum. In hyperclean mice (previously made germfree and then colonized with a limited flora nonpathogenic to mice) antibody given intravenously was ineffective. The effects of antibody and nonspecific stimulation of cell-mediated immunity (after previous infection with Histoplasma capsulatum) were additive in increasing host resistance to murine C. trachomatis.