Anti-Thy-1 antibody provokes reverse passive cutaneous anaphylaxis-like reactions

Antibodies to rat Thy-1, and also to murine Thy-1, could provoke reverse passive cutaneous anaphylaxis-like (RPCA-like) reactions. The threshold amount of purified anti-Thy-1 antibodies for RPCA-like reactions was 12.5 microg/ml. No RPCA-like reactions were obtained with IgG1 F(ab')2 anti-Thy-1. Cross-linking the murine anti-rat Thy-1 F(ab')2 fragments with goat antibody against murine F(ab')2 anti-rat Thy-1 permitted us to obtain RPCA-like reactions with as little as 1.5 microg/ ml. However, when the cross-linking was done with the F(ab')2 of the same goat antibody, no RPCA-like reactions were obtained. The antibody against rat FcepsilonRIalpha or its F(ab')2 product were equally effective in producing RPCA-like reactions; the threshold was obtained with 1.5 microg/ml. The mechanism of the difference is discussed.