A passive transfer model of the organ-specific autoimmune disease, bullous pemphigoid, using antibodies generated against the hemidesmosomal antigen, BP180.(1)
Herpes gestationis (HG) were also shown to produce complement-fixing IgG autoantibodies that exhibit a linear basement membrane zone (BMZ) staining pattern identical to that of Bullous pemphigoid (BP) autoantibodies. All of these findings are consistent with a pathogenic mechanism whereby autoantibodies bind to their target antigens in the BMZ, activate complement, and induce subepidermal vesiculation by triggering inflammation. Both of these autoantigens, designated BP180 and BP230, have been localized to the epidermal hemidesmosome, a cellular structure involved in anchoring basal keratinocytes to the basement membrane.
Identified on this diagram is a 14-amino acid stretch within a non collagenous region of the BP 180 ectodomain that was shown by epitope mapping analysis to be a major site of reactivity for both BP and HG autoantibodies. Amino acid sequence alignment of the human and murine BPI 80 sequences are shown. Only 3 of the 14 residues in this antigenic region are identical in these two species.
The rabbit anti-human BP180 anti-serum, R306, reacted with the human BP180 polypeptide from GST-NAl but did not react with the murine BP180 homologue. Conversely, the rabbit anti-murine BP180 antiserum, R140, reacted with the murine but not the human form of BP180.
24 h after intraperitoneal injection of rabbit anti-murine BP 180 IgG into neonatal BALB/c mice (12-36 h of age) the skin of the injected animals was markedly erythematous and, upon gentle friction, developed persistent epidermal wrinkling producing the “epidermal detachment” sign. Mice injected with doses of > 2.7 mg/g body weight developed extensive (3+) disease. Animals injected with lower doses (270 ug/g body weight and 27 ug/g body weight) exhibited minimal ( 1 +) reaction or no reaction, respectively.
Injections of 13.5 mg IgG/g body weight triggered an acute inflammatory response (2+ reaction) that involved an area 8 mm in diameter. The erythematous reaction was less intense ( 1+ reaction) and smaller in diameter (4 mm) at sites injected with 1.35 mg IgG/g body weight, and was absent at sites injected with 135 ug IgG/g body weight.
Mice injected with the lowest dose of IgG (27 ug/gbody weight) did not have detectable levels of circulating rabbit anti-murine BPI 80 IgG nor did they show signs of skin disease, although low levels of tissue-bound rabbit IgG and mouse complement were detected at the cutaneous BMZ of these animals. Extensive disease (3+) and high titers of circulating anti-murine BMZ antibodies ( 1: 160) were observed in animals treated with a high dose of rabbit anti-murine BP 180 IgG (2.7 mg/g body weight), but detection of in situ bound immune reactants was variable and appeared to be site dependent in these animals. Mice injected with anti-human BPl 80 IgG (0.27 and 2.7 mg/g body weight) developed high titers of circulating antibody (1:160-640) when assayed by indirect IF against normal human skin.
Similar to the dose response observed with the intraperitoneal injections, an increase in the dose of anti-murine BP180 IgG given intradermally resulted in an increase in the titer of anti-murine BMZ antibodies were detected in the serum of the injected mice and in an increase in local skin disease activity.