The major histocompatibility complex (MHC) of the domestic cat (termed FLA) has been refractile to genetic and serological definition largely because of repeated failure to detect cytotoxic antibodies in multiparous cats or to elicit antibody following allogeneic lymphocyte immunization. We have developed a protocol for producing cytotoxic alloantisera in the cat following rejection of multiple surgical skin grafts. Of 59 cats subjected to grafting, 13 produced lymphocytotoxic antisera which had varying specificities among a panel of outbred cat cells. A population cluster analysis of the 13 alloantisera permitted the identification of six clusters of overlapping FLA specificities. The major histocompatibility complex (MHC) is a multigene cluster in mammals encoding two distinct classes of molecules involved in the presentation of foreign antigen to the T-cell receptor (1-5). Class I genes encode a 45-kDa glycoprotein that is noncovalently linked with an invariant light chain, P2-microglobulin (f82m), on the surfaces of virtually all nucleated cells (4, 6). Class II genes encode the heavy (32-35 kDa) and light (25-28 kDa) subunits of the noncovalently associated af3 heterodimeric glycoproteins expressed on the surfaces of antigen-presenting cells and activated T cells (5). By serological analysis, both class I and class II antigens are abundantly polymorphic in most outbred species. DNA restriction analysis has also revealed extensive polymorphism of the MHC of mice, humans, and several other species (7,8). The function of both class I and class II antigens is to present foreign, often viral, antigen to the T cell receptor. In this way, the cellular immune response is directed to parasitized cells instead of free virus particles (9,10).The domestic cat is an important model for at least two viral diseases of the immune system in humans, human T cell leukemia and acquired immunodeficiency syndrome (AIDS) (11,12). The characterization of the feline MHC as a prerequisite for the study of disease progression has been difficult because of an apparent inability to raise typing alloantisera in the cat (13
MATERIALS AND METHODSDetails of allograft transplantation are described elsewhere (ref. 21; C.W. and S.O., unpublished data). Briefly, split thickness skin grafts were surgically exchanged between selected cats at 21-day intervals. In some cases, intraperitoneal booster injections of peripheral blood lymphocytes (PBLs) from 15 ml of blood were performed at 4-day intervals after grafting (21). Serum was collected from graft cats weekly and used in a cat complement-dependent cytotoxicity assay. A modification of a two-stage assay using 51Cr release as an indicator ofcell death was used to detect alloantibodies against donor cat lymphocytes. The monoclonal antibody W6/32 (23), specific for human class I heavy chain, and the monoclonal antibodies IB5 (human DR and DQ specific) (24) and ISCR3 (mouse I-EK specific) (25) were used as positive controls in immunoprecipitation experiments.Interleukin 2-stimulated or fr...