The gene encoding the Ia antigen-associated invariant chain (Ii) is not linked to the H–2 complex

Abstract

The invariant (I_i) chain of murine Ia antigens is associated with the intracellular but not the cell-surface forms of the A_α:A_β and E_α:E_β Ia complexes^1–3. Due to its unique subcellular localization, I_i has been postulated to play a part in the assembly⁴ or intraceUular transport² of the Ia α:β complexes, which function in immune recognition^5–7. A more general role for I_i in the transport of other cell proteins has also been suggested⁸. Because of the unusual subunit composition of Ia antigens and because the synthesis of α, β and I_i chains is coordinately regulated⁹, it was of interest to determine whether, like the α and β chains^10–12, I_i is encoded by a gene in the I region of the H–2 histocompatibility complex. We report here the use of an I_i chain polymorphism present in Mus spretus¹³ to demonstrate that the gene for I_i is not linked to the H–2 complex. Thus, intracellular Ia antigens consist of the products of two linked genes and one unlinked gene.