These data suggest that the line 6 TCR Vβ1 repertoire has been selected away from a “best-fit” relationship between the SHKESVIQTMF motif and at least one of the B2-encoded MHC molecules; this could provide increased protection from MD either by maximizing the use of different TCRs that better recognize MD antigens, especially on MHC class I, or by reducing the availability of activated CD4+ target cells for MDV infection. Here, CD4 is linked to Menkes disease.