IMMUNE-RESPONSE TO SHEEP RED-BLOOD-CELLS IN 2 SMYTH LINE POPULATIONS HOMOZYGOUS FOR DIFFERENT MAJOR HISTOCOMPATIBILITY COMPLEX HAPLOTYPES

The Smyth line (SL) chicken is characterized by a high incidence of sp ontaneous, 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 f emales from 2 SL sublines (SL101 and SL102), each homozygous for a dif ferent MHC haplotype, their MHC-matched parental control sublines (BL1 01 and BL102), and a normally pigmented control, LBL. Although total i ncidence of amelanosis is approximately the same for both SL sublines, amelanosis occurs earlier and is more severe in SL101 birds. Within s ublines, chickens were further classified as to the extent of the feat her amelanosis. Neither SL MHC subline had a mean SRBC titer that diff ered significantly from unrelated LBL controls. Although the secondary response of the two sublines differed from each other (P < .05), neit her differed from its MHC-matched parental control; therefore, the dif ferences in immune response appear to be largely MHC-related and not c losely related to melanocyte destruction. When SRBC titers were relate d to amelanotic severity, no differences were found within the SL101 s ubline, although, SL102 birds that became amelanotic at a later age ha d a lower primary response to SRBC (P < .05) than the more severely af fected group. Birds simultaneously producing both pigmented and amelan otic feather tissue had higher (P < .05) primary and secondary anti-SR BC titers than did the complete amelanotics.