Immunogenetic analysis of microsomal and non-microsomal lipoproteins from normal and malignannt mouse tissues for histocompatibility-2 (H-2) antigens

Intracellular localization and immunogenic capacities of phenotypic products of mouse histocompatibility genes

The transplantation antigens are the phenotypic products of genes which control histocompatibility in vertebrate species. The products of major histocompatibility locus of the mouse, H-2, have been studied as a model. The H-2 transplantation antigens are expressed on cellular membranes in all tissues examined. These gene products have been isolated from cells associated with subcellular membranes. These membranes have been assayed both for their antigen content (antigenicity) and for their capacities to induce a primary humoral and a cell-mediated response (immunogenicity). In all tissues examined, the H-2 antigens (products of the K and D regions of H-2) were found expressed in high concentration on cell surface membrane. However, immunogenic activity was observed only with spleen and thymus preparations, consisting mainly of intracellular membranes (MLP). Immunogenic MLP was also isolated from lymphoblast and fibroblast cells, and again was derived mainly from endoplasmic reticulum. In other tissues, such as liver, kidney, and erythrocytes, H-2 antigens were found only on surface membrane and in an antigenic but nonimmunogenic form. A novel method for tagging surface membrane of mammalian cells is presented. It consists of binding, to whole cells in a covalent linkage, purified preparations of the beta-galactosidase of E. coli. The bound enzyme has proved to be an unambiguous marker for surface membrane. With this marker, the stability of surface membrane to shear forces during homogenization could be assessed. A number of considerations suggest that immunogenicity of transplantation antigens may be due to factor(s) present on the membranes in addition to the H-2 antigenic determinants. There are indications that these factors may be controlled by the I region of the H-2 complex. It is interesting to note that normal tissues which have Ia antigens on their surface membranes yield immunogenic MLP (spleen and thymus), whereas those without Ia surface antigens yield an antigenic MLP that has no immunogenic capacity (liver, kidney, and erythrocytes).

Induction of the immune response to cell surface antigens in vitro

Two tissue culture incubation systems are described in which immune responses to cell surface antigens have been demonstrated. In the one-way "mixed lymphocyte interaction" system, a specific stimulation of thymidine uptake was induced by a particulate membrane antigen fraction, the microsomal lipoproteins (MLP), when low levels (0.01 to 0.001 mug per ml) were incubated with spleen or lymph node cells from nonsensitized mice. No stimulation was seen when allogeneic MLP was used at high levels, 10 mug per ml, nor at any level with syngeneic MLP. Specific effectors were demonstrated after 72-hr incubation with stimulatory levels of allogeneic MLP in three separate in vitro assays, a plaque-forming cell reduction assay, a tumor target assay, and an antigen-binding cell assay. In the latter assay, [125I]MLP was used as the source of antigen. This system has limited potential inasmuch as mouse spleen cells do not survive in it beyond the 4th day of culture. The second tissue culture system, the Marbrook system, has much greater possibilities because at least 25% of the inoculum is recovered 7 days later. In this culture system a cell-free sheep erythrocyte membrane preparation can induce plaque-forming cells in the absence of macrophages. Using a sensitive radioimmunoassay, free specific antibody was detected in culture supernatant fluids. With the same culture system, allogeneic lymphocytotoxic cells (killer) have been induced with spleen cells from unprimed mice in strains differing at the major histocompatibility locus (H-2). Allogeneic MLP induced very significant "killer" cell activity with spleen cells from primed mice. In a syngeneic tumor system, significant amounts of killer cell activity were induced with unprimed spleen cell inocula, and much larger amounts induced with spleen cells from immunized mice.