Potential relationships between amino acid motifs of various alleles of the ovine major histocompatibility complex DR (Ovar-DR) molecule and occurrence of clinical OPA caused by JSRV were investigated in a case-control study. Latxa sheep (n = 132) screened for presence/absence of pulmonary OPA lesions were typed for their Ovar-DRB1 2nd exon alleles by PCR and sequence-based typing (PCR-SBT). The polymorphic amino acid residues derived from the obtained 34 DRB1 protein variants were subjected to a logistic regression-based association study. The amino acids at several positions showed significant associations with the presence/absence of pulmonary OPA lesions: some of the residues were located within the peptide binding cleft of the DRB molecule, including pockets P1, P4, P7 and P9. (C) 2012 Elsevier Inc. All rights reserved.