Identification of antigenic epitopes in type IV collagen by use of synthetic peptides

Peptides representing potential antigenic regions of the NC-I and 7-S domains of the human α1 and β2, and bovine α3 chains of type IV collagen were synthesized either chemically or by the recombinant DNA technique and tested by ELISA using antibodies raised in rabbits against the whole type IV collagen or the NC-1 domain.¹ Sera from patients with Goodpasture syndrome (GP) or with acute poststreptococcal glomerulonephritis (APSGN) were also tested. The location of antigenic determinants was predicted from the primary and secondary structure of the chains, that is, aromaticity, hydrophilicity and presence of β-turns. All synthetic peptides reacted with the antiserum to type IV collagen (anti-Col IV). Whereas all peptides arising from the NC-I domain reacted with anti-NC-1, intact 7-S or peptides of the α1 or α2 chain of the 7-S domain did not react. However intact 7-S reacted with anti-Col IV. Two synthetic peptides from the NC-I domain of α1, (a.a. 71-90 and a.a. 176-190), one from the α2 (a.a. 70-83) and four from the α3 chain (a.a. 72-89, a.a. 104-117, a.a. 133-145, a.a. 185-203) reacted with anti-NC-1 and anti-COL IV. The above peptides, except α3 (72-89) and α3 (185-203), were tested and found to be reactive with sera from patients with GP. Intact 7-S reacted with several sera from patients with GP; however, only two synthetic peptides from the 7-S domain of the α2 chain reacted with two of the GP sera. One serum from a patient with GP reacted with intact 7-S but not with NC-I. More than the presence of β-turns and hydrophilicity, the single most consistent predictor of immunoreactivity of synthetic peptides from the NC-1 domain was the presence of aromatic amino acids. Sera of patients with APSGN reacted exclusively with the 7-S domain. This reactivity resided in the synthetic peptide α2(IV) 1-18 from the 7-S domain. The results show that this approach can be used to define more precisely the nature of antigenic epitopes that may be involved in the mediation of immunologic injury in renal disease.