Sheep major histocompatibility (OLA) complex: apparent involvement in a flock endemic infection by Corynebacterium pseudotuberculosis.

In a Préalpe flock with endemic infection by Corynebacterium pseudotuberculosis, some sires seem to have transmitted some resistance traits not yet genetically defined. In sire progenies including offspring with and without abscess, abscesses occurred independently of the transmitted sire's OLA haplotype. However, in all considered offspring, some OLA antigens were positively or negatively associated with the delayed occurrence of abscess. The three antigens OLA-A4, A10, B6 were positively associated with delayed abscess and negatively with early abscess. Conversely, antigen OLA-A2 was negatively associated with delayed abscess and to a less extent positively with early abscess. When the three following groups of offspring without abscess (a), with late abscess (b) and with early abscess (c) were compared, frequencies of genes OLA-A4, A10, B6 on the one hand, OLA-A2 on the other hand, varied inversely, which shows that the OLA complex is linked to, at least, one locus from which the genes are implied in the delay of abscess formation (or precocity). Similarly, antigen OL-X5, loosely linked with the OLA complex, appeared to be positively associated with recurrent abscess and negatively with unique abscess. The observed associations were probably caused by linkage disequilibria between OLA (and OL) genes and genes influencing either the abscess delay or recurrence.