Search

Killer toxin-neutralizing monoclonal antibody (nmAb-KT) against HM-1 killer toxin (HM-1) produced by yeast Williopsis saturnus var. mrakii IFO 0895 reduces both the killing and glucan synthase inhibitory activity of HM-1. nmAb-KT is classified as IgG1kappa and has been shown to be ineffective against HYI killer toxin produced by the related yeast W. saturnus var. saturnus IFO 0117. To determine the epitope for nmAb-KT, overlapping peptides were synthesized from the primary structure of HM-1. nmAb-KT reacted with peptides P5 (33NVHWMVTGGST43), P6 (39TGGSTDGKQG48) and P7 (44DGKQGCATIWEGS56), which represent the middle region of the HM-1 sequence. P6 reacted most strongly with nmAb-KT. Combined analysis by immunoblotting, surface plasmon resonance (SPR) analysis and yeast growth inhibition assay showed that nmAb-KT recognizes a specific epitope within peptide P6. The K(d) value of nmAb-KT against HM-1 and P6 were determined to be 5.48 x 10(-9) M and 1.47 x 10(-6) M by SPR analysis, respectively. These results strongly indicate that nmAb-KT binds to HM-1 at the sequence 41GSTDGK46, and not to HYI at the same position. The potential active site of HM-1 involved in the killing activity against sensitive yeast is discussed.

A murine mAb (mAbKT4, IgG1) that neutralized in vitro the anti-Candida activity of a killer toxic (KT) from the yeast Pichia anomala acted as an idiotypic (Id) vaccine in eliciting anti-Id Abs with toxin-like activity (KT-IdAb) in a rat vaginitis model. In this study, we demonstrate that intravaginal or intragastric inoculations of Candida albicans bearing a receptor for the toxin was able to recall KT-IdAb production in the vagina of the animals primarily immunized with mAbKT4 and also to elicit by themselves an Ab that functionally mimicked the KT (KTAb). Anti-Id-like, KT-like Abs were also consistently found in the vaginal fluid of human vaginitis patients who were infected by Candida but who had never been exposed to the Id vaccine. These Abs were as candidacidal in vitro as those raised in rat vagina by the Id vaccination, and, likewise, their cytocidal effect was totally neutralized by previous reaction with mAbKT4. Importantly, they were also able to confer a significant anticandidal protection in the rat vaginitis model, comparable to that achievable by KT-IdAb passively transferred to naive rats from Id-vaccinated animals. Thus, candidacidal Abs representing the internal image of a yeast KT are part of the Ab repertoire that follows infection or immunization with Candida. It is speculated that the host's immune system response may exploit the KT receptor of microbial pathogens to produce microbicidal Abs, possibly mirroring competition events among microorganisms in natural habitats.