Influence of genotypes at a non-MHC B lymphocyte alloantigen locus (Bu-1) on expression of Ia (B-L) antigen on chicken bursal lymphocytes.

Two inbred lines of chickens known to be identical at the MHC differ in their expression of Ia antigen on cells of the bursa. Line 6 bursas had 23% of intensely staining Ia+ cells while line 7 bursas had a much higher level, 85%. Studies of F4 progeny of line 6(3) X 100 crosses showed that genetic control of the high bursal proportion of Ia+ cells was determined by the Bu-1 alloantigen system. Line 100 is identical to line 7 for the lymphocyte alloantigens identified by the T and B cell reagents used in this study. Tests of F4 heterozygotes at the Bu-1 locus show a dominant effect of the Bu-1b gene in control of a high proportion of strongly staining Ia+ cells in the bursa.