Alloimmune interactions of a lymphoproliferative disease-inducer gene Arp and linkage to Pep-7.

In this report we describe a new diallelic gene system, Arpa and Arpb, which codes for surface antigens on murine lymphocytes. Arpb is present only in a mutant strain of BALB/c which is designated BALB/c-Arpb. Normal BALB/c and all other strains of mice tested express Arpa. The Arpb mutation is associated with a newly discovered polymorphism of the Peptidase-7 enzyme, Pep-7b, which codes for a variant form of the enzyme with a faster anodal mobility on electrophoresis than the commonly known form. The Arp locus controls a range of alloimmune interactions between Arp incompatible lymphocytes. These include mixed lymphocyte reactivity, host-versus-graft and graft-versus-host reactions and the development of weak cytotoxic but strong cytostatic effector lymphocytes which are allo- as well as autoreactive. The association between Arp and Pep-7 and the biological significance of the Arp locus are discussed.