Immune response to sheep red blood cells in two Smyth line populations homozygous for different major histocompatibility complex haplotypes.

The Smyth line (SL) chicken is characterized by a high incidence of spontaneous, posthatch, selective destruction of melanocytes, caused by an autoimmune phenomenon. It has been shown that the MHC is associated with the development and severity of the disease. To clarify further the role of MHC haplotypes and other factors leading to an autoimmune response, mean antibody titers to SRBC were determined for 37-wk-old females from 2 SL sublines (SL101 and SL102), each homozygous for a different MHC haplotype, their MHC-matched parental control sublines (BL101 and BL102), and a normally pigmented control, LBL. Although total incidence of amelanosis is approximately the same for both SL sublines, amelanosis occurs earlier and is more severe in SL101 birds. Within sublines, chickens were further classified as to the extent of the feather amelanosis. Neither SL MHC subline had a mean SRBC titer that differed significantly from unrelated LBL controls. Although the secondary response of the two sublines differed from each other (P < .05), neither differed from its MHC-matched parental control; therefore, the differences in immune response appear to be largely MHC-related and not closely related to melanocyte destruction. When SRBC titers were related to amelanotic severity, no differences were found within the SL101 subline, although, SL102 birds that became amelanotic at a later age had a lower primary response to SRBC (P < .05) than the more severely affected group. Birds simultaneously producing both pigmented and amelanotic feather tissue had higher (P < .05) primary and secondary anti-SRBC titers than did the complete amelanotics.