[The mechanism of antigen-antibody reaction at the basement membrane zone in bullous pemphigoid. The question of interaction of complement factors and bivalent cations (author's transl)].

1. In a medium poorly cationic indirect immunfluorescence of the basement membrane zone normally observed with preparations of sera from patients with pemphigoid has not be seen. 2. The fluorescence of basement membrane zone takes place if Fe2+ ions are added together with the antibasement zone antibodies. Evidently Fe2+ ions are essential for fixing antibodies. 3. With the method of indirect fluorescence the C3 component of complement could be observed after fixation of pemphigoid antibodies to the basement membrane zone. 4. EDTA prevents binding C3 too. Only after adding Fe2+ (not with Ca2+ or Mg2+) complement IF staining is demonstrable. Apparently EDTA causes the loss of fixing antibasement zone antibodies at first. Thereafter complement staining reaction is negative. 5. Participation of C1 could not be demonstrated using indirect IF staining. The alternate pathway to activation of C3 is discussed.