New lymphocyte antigen system (Lna) controlled by the Ir region of the mouse H 2 complex

A new system of lymphocyte alloantigens in mice is described. This Lna (lymph node antigen) system is associated with the Ir region of the H-2 (histocompatibility-2) gene complex. It has the following distinctive characteristics: The gene or genes controlling these antigens has been mapped in the Ir (immune response) region between H-2K and Ss-Slp. The antigens are most readily detectable on lymph node cells, although they are also expressed on peripheral blood lymphocytes, splenic lymphocytes, and thymocytes. Cytotoxicity against only about half of lymph node cells is consistently observed. Cytotoxic antibody titers against these antigens are strikingly high, more than 2000 by ⁵¹Cr release and up to 100,000 in the microcytotoxic test. At least two, probably allelic, forms of the antigen(s) have been defined, one associated with the H-2(k) haplotype and one with the H-2(s) haplotype. Antisera against Lna contain multiple antibody specificities that can be fractionated by absorption either with certain recombinants or with other H-2 haplotypes that have crossreactive antigens. The antisera against Lna may be of value for definition and characterization of the products of the Ir and MLR (mixed lymphocyte reaction stimulatory) genes associated with the H-2 complex.