An Ly-like specificity with extensive nonlymphoid expression

Membrane defence against complement lysis: the structure and biological properties of CD59

The complement system is an important branch of the innate immune response, constituting a first line of defence against invading microorganisms which activate complement via both antibody-dependent and -independent mechanisms. Activation of complement leads to (a) a direct attack upon the activating cell surface by assembly of the pore-forming membrane attack complex (MAC), and (b) the generation of inflammatory mediators which target and recruit other branches of the immune system. However, uncontrolled complement activation can lead to widespread tissue damage in the host, since certain of the activation products, notably the fragment C3b and the C5b-7 complex, can bind nonspecifically to any nearby cell membranes. Therefore it is important that complement activation is tightly regulated. Our own cells express a number of membrane-bound control proteins which limit complement activation at the cell surface and prevent accidental complement-mediated damage. These include decay-accelerating factor, complement receptor 1 and membrane cofactor protein, all of which are active at the level of C3/C5 convertase formation. Until recently, cell surface control of MAC assembly had been attributed to a single 65-kD membrane protein called homologous restriction factor (alternatively named C8-binding protein and MAC-inhibiting protein). However a second MAC-inhibiting protein has since been discovered and it is now clear that this protein plays a major role in the control of membrane attack. This review charts the rapid progress made in elucidating the protein and gene structure, and the mechanism of action of this most recently discovered complement inhibitor, CD59.

The CD59 antigen is a structural homologue of murine Ly-6 antigens but lacks interferon inducibility

A cDNA encoding the human leukocyte antigen CD59 has been isolated from the erythroid cell line K-562 and its identity confirmed through expression in COS cells. Northern blotting reveals three message species of approximately 800, 1400 and 2000 bases in size, which are constitutively expressed in all lymphoid, erythroid, myeloid, and neural cell types tested thus far. Southern blotting of human DNA indicates a pattern consistent with the presence of a single gene, which has been mapped to chromosome 11 by somatic cell hybrids. Also, the finding of a transcriptionally active cross-hybridizing gene in monkey cells suggests conservation of CD59 sequences among primates. Comparison of the CD59 protein sequence with those of the Ly-6E and Ly-6C antigens discloses a similarity in overall structure, including the alignment of abundant cysteine residues, hydrophobic carboxy termini and conservation of amino acids surrounding the proposed phosphatidylinositol-glycan modification site for Ly-6 molecules. Unlike Ly-6, however, CD59 expression does not appear to be inducible with interferons. This, along with its limited homology and different tissue distribution, cast doubt upon the functional equivalence of CD59 and either of the well-characterized mouse Ly-6 proteins.

Kinetic analysis of Ly-6 gene induction in a T lymphoma by interferons and interleukin 1, and demonstration of Ly-6 inducibility in diverse cell types

The Ly-6 locus contains multiple genes encoding cell surface proteins, two of which, when cross-linked by antibodies, effect antigen-independent activation of T lymphocytes. In this study, cDNA for Ly-6-encoded antigens have been used as probes to examine RNA from various tissues and transformed cell lines for constitutive levels of Ly-6 RNA expression. Analyses of RNA prepared from several different tissues revealed a high level of expression of Ly-6 RNA in kidney, spleen, heart and thymus, with a more moderate level of expression in liver, brain and lung tissue cells. A survey of various cell lines demonstrated the presence of Ly-6 RNA in many, but not all T lymphocytic cell lines, in L cells, the Meth A fibrosarcoma, in the TCMK kidney cell line, and in the Neuro-2a neuroblastoma. We also evaluated the expression of Ly-6 RNA in cells after treatments with interferons (IFN) and interleukin 1 (IL1). Treatment of lymphoid cells with IFN (alpha/beta and gamma), known to increase cell surface Ly-6 antigen expression in normal T cells, was correlated with increases in Ly-6 RNA levels. Increases in levels of RNA correlated with increases in levels of the Ly-6A/E or Ly-6C antigens. Several T lymphoid cell lines exhibiting Ly-6 RNA inducibility by IFN were similarly inducible with IL1. Kinetic experiments using one such line, (YAC-1), showed that the induction of Ly-6 RNA mediated by IFN-alpha/beta occurred rapidly (within 4 h), while the induction by IL1 required relatively more time (approximately 8 h). Although the actions of IFN-alpha/beta were not blocked by cycloheximide, the presence of this protein synthesis inhibitor significantly attenuated the effects of IL1 and IFN-gamma on Ly-6 RNA transcription. Induction by IFN-gamma as well as IL1 could be blocked completely by co-culture with anti-IFN-gamma, implicating IFN-gamma as a mediator of the induction by IL1.

Differential resistance to growth of a tumor expressing incompatible minor alloantigens reflects regulatory influences rather than differences in anti-minor-CTL-P frequencies

In previous studies it was found that BALB/c (H-2d) was more susceptible than (BALB/c X A)F1 (H-2d X H-2a) to a tumor bearing multiple mismatched minor histocompatibility antigens, the DBA/2 (H-2d) mastocytoma P815, and that this resistance was H-2 linked. In the present studies the immunologic basis of this effect was examined by comparing the cytotoxic-T-lymphocyte (CTL) responses of BALB/c with those of (BALB/c X A)F1. Despite the BALB/c X A)F1's 34-fold greater resistance to P815 in vivo, the numbers of effector cell precursors were found to be similar in the two hosts as shown by (a) similar anti-P815 CTL responses in vitro with T-cell growth factor, (b) similar secondary anti-DBA/2 MiHA responses after in vivo priming with irradiated P815, and (c) similar frequencies of anti-DBA/2 CTL precursors by limiting-dilution analysis. However, priming with proliferating P815 in vivo revealed a defect in the BALB/c animals: Spleen cells from such animals were unable to control the growth of contaminating P815 cells in vitro or to mount strong secondary CTL responses to DBA/2 antigens. The defective priming of BALB/c could be corrected when DBA/2 spleen cells were added to the P815 inoculum. This impaired priming by living tumor cells was not seen in (BALB/c X A)F1. It is concluded that the use of living P815 tumor cells revealed a defect in immunoregulation in BALB/c mice, which rendered them susceptible to tumor growth in spite of apparently adequate numbers of anti-minor-CTL precursors. How the additional H-2 products expressed in the (BALB/c X A)F1 might correct this defect is discussed.

Studies of the mouse Ly-6 alloantigen system. II. Complexities of the Ly-6 region

The discovery of several monoclonal antibodies provided the impetus to revisit the Ly-6 group of antigens. Our serological data point to the existence of at least five separate Ly-6 antigens. They are distinguished by the patterns of their tissue expression as (1) the classical Ly-6 alloantigen of peripheral lymphocytes (Ly-m6.2A), (2) a bone marrow cell-restricted antigen (Ly-m6.2B), (3) an antigen shared by bone marrow cells and peripheral lymphocytes (Ly-m6.2C, possibly identical with H9/25), (4) an antigen expressed on bone marrow cells, thymocytes, and peripheral lymphocytes (Ly-m6.2D), and (5) an antigen occurring exclusively on lymphoblasts (Ly-m6.1E, similar to Ala-1). ThB is a sixth distinct antigen of the group. The assumption that separate antigens exist is supported by distinctive distribution patterns in normal and neoplastic tissues. The genes controlling Ly-6 antigens are closely linked, as they are transmitted as two haplotypes only. One incidence of a crossover within the Ly-6 region was observed: the Ly-6B.2 alloantigen was expressed in NZB mice, which type Ly-6.1 for other Ly-6 specificities.

Different expression of Lyt differentiation antigens and cell surface glycoproteins by a murine T lymphoma line and its highly metastatic variant

Cloned lines of the methylcholanthrene-induced DBA/2 T lymphoma Eb and its highly metastatic variant line ESb were analyzed for differences in the expression of serologically detectable cell surface differentiation markers. Flow cytofluorographic analysis of cells stained with fluorescein isothiocyanate-conjugated monoclonal rate anti-mouse Thy-1, Lyt-1, Lyt-2 and complement-dependent cytotoxicity with mouse alloantisera against Lyt-3.2 and Ly-6.2 revealed, for the parental low metastasizing line, Eb, a phenotype of Thy-1+, Lyt-1-, Lyt-2+, Lyt-3+, Ly-6+, whereas the highly metastasizing variant line typed as Thy-1-, Lyt-1+, Lyt-2-, Lyt-3-, Ly-6-. Analysis of galactose oxidase/NaB3H4-labeled glycoproteins from Eb and ESb clones by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate showed further phenotypic differences. Selective binding of radiolabeled glycoproteins to Helix pomatia or Vicia villosa-Sepharose, respectively, allowed the identification of T130 to be expressed on Eb cells and T145 to be expressed on some ESb clones. The latter antigen is expressed on murine cytotoxic T lymphocytes. Immune precipitation analysis revealed that Eb and ESb bear different molecular forms of the T200 antigen. Comparisons of iodinated surface proteins derived from tumor cells either treated or untreated with tunicamycin indicated that many of the differences in membrane proteins between Eb and ESb cells could be attributed to differences in glycosylation. Our results, derived from a defined tumor system of lymphoid origin, show that the progression from a low to a high malignant tumor line can be associated with changes in the expression of various defined cell surface differentiation antigens. The question of a possible relationship between tumor progression and cell differentiation or dedifferentiation is discussed.

Evidence for expression of Ly-6.2 on non-bone marrow-derived cells in kidney, skin and connective tissues

Mouse alloantigen Ly-6.2 is detectable in various non-lymphoid tissues such as kidney, but it is not clear whether or not this expression is due to bone-marrow derived passenger leukocytes. To determine whether non-marrow derived cells express Ly-6.2, we examined the expression of this antigen in kidney and on isolated connective tissue and epidermal cells. Studies in radiation chimeras demonstrated that the kidney did not become Ly-6.2 positive when negative animals were reconstituted with positive marrow. Thus, passenger leukocytes cannot account for the renal expression of Ly-6.2, indicating that most of this antigen is on non-marrow-derived (parenchymal) cells in kidney. Various isolated cell types--fibroblasts, osteocytes, chondrocytes and skin epidermal cells--were found to be Ly-6.2 positive. Indeed, absorption and cytotoxicity results suggested that the amount of Ly-6.2 on fibroblasts exceeded the amount of an H-2 antigen on these cells. Comparison of fibroblasts to lymphocytes indicated that fibroblasts had 13--60 times more Ly-6.2 than spleen cells and three times more than PHA blasts. The results indicate that the Ly-6.2 detected in non-lymphoid tissues is predominantly on the parenchymal or connective tissue elements of those tissues.

Immunoselection in vitro of a non-metastatic variant from a highly metastatic tumor

Immunoselection of a non-metastatic variant of the highly metastatic MDAY-D2 tumor of DBA/2 mice was achieved by means of an antiserum directed to the LY6.2 surface marker of MDAY-D2. While the new tumor (MDAY-D2.L61) expresses no detectable LY6.2, other measurable surface markers including H2d, FcR and TAA remain unchanged. The phenotypic behavior of MDAY-D2.L61 is that of a non-metastatic tumor and has remained stable after 1 year of maintenance in vivo and in vitro. Immunoselection can now be used to derive variants with stable phenotypic behavior from heterogeneous parent tumor cell populations.

Ly-6 region regulates expression of multiple allospecificities

The relationship between two alloantigens on mouse lymphocytes, that is Ly-6.2 and H9/25, which have previously been shown to have identical strain distribution patterns, was further investigated. Analysis of 39 (AKR x CBA) x CBA backcross progeny showed no segregation between these two antigens, indicating a close genetic linkage between them. Serological analysis showed that Ly-6.2 and H9/25 are differentially expressed on T-cell hybrid lines. Furthermore, cross-absorption of anti-Ly-6.2 serum with two cell lines revealed a heterogeneity among Ly-6 specificities. Semipurified H9/25 antigen failed to block anti-Ly-6.2 serum while anti-Ly-6.2 serum did not significantly block monoclonal antibody H9/25. These results suggest the presence of multiple allospecificities encoded for by the Ly-6 region.

Studies of the mouse Ly-6 alloantigen system. I. Serological characterization of mouse Ly-6 alloantigen by monoclonal antibodies

Three monoclonal antibodies were produced by fusing mouse myeloma cell line NS-1 with spleen cells from C3H/An mice hyperimmunized with B6-H-2k spleen cells. These antibodies recognized an alloantigen displaying a similar strain distribution pattern to the Ly-6.2 and Ala-1.2 alloantigens. Analysis of CxB and BxH recombinant inbred mice revealed close linkage of genes controlling Ly-m6 and Ly-6. The monoclonal antibodies lysed 70 percent of cells in lymph nodes and 60 percent in spleen in direct cytotoxicity assays, but did not lyse significant numbers of cells of thymus and bone marrow. Separated T and B cells were reactive with the antibodies, but T cells were more sensitive to the antibody and complement than B cells. Virtually all cells in cultures of cells activated in the mixed lymphocyte reaction or by Concanavalin A were reactive with the monoclonal antibodies. Direct plaque-forming cells were completely eliminated by the monoclonal antibody and complement. By absorption tests, cells from all organs tested so far (thymus, lymph node, spleen, bone marrow, brain, kidney and liver) were shown to express the Ly-m6 determinant. Tumor cell lines with T, B or stem cell characteristics were reactive with the monoclonal antibody by direct cytotoxicity and absorption assays.

Monoclonal antibodies to ThB detect close linkage of Ly-6 and a gene regulating ThB expression

We have generated three hybridomas producing rat monoclonal antibodies to a surface antigen, ThB, that is shared by murine B lymphocytes and approximately 50 percent of murine thymocytes. These antibodies, produced by immunizations with MOPC-104E cells, appear to recognize the same antigen that was previously detected by rabbit and goat antisera to MOPC-104E cells (Yutoku et al. 1974, Yutoku et al. 1976). Using these antibodies, we have studied a genetic polymorphism that is associated with the level of ThB expression on B lymphocytes but not with the antigen's expression on thymocytes. We present evidence that this trait is controlled by one gene, Thb, which we find to be very closely linked to the gene or genes controlling the Ly-6, Ly-8, DAG, and Ala 1 antigen(s). While the latter four antigens were described as markers on mature T (or activated T and B) lymphocytes, ThB is restricted to immature thymocytes and all B cells. ThB is not expressed on kidney, although some investigators (McKenzie et al. 1977 a, Halloran et al. 1978) report Ly-6 expression on that tissue. SJL/J, C57BL/10JHz, DBA/2J, and AKR/J are among the mouse strains carrying the Thbh allele, while BALB/cN, CBA/J, C3H.SW/SnHz, and A/J carry the Thb1 allele. The ThB antigen has not yet been identified as a glycoprotein after cell-surface iodination, NP-40 solubilization, and immunoprecipitation.

H 9/25 monoclonal antibody recognizes a new allospecificity of mouse lymphocyte subpopulations: strain and tissue distribution

C3 H/He-mg mice were immunized with C57BL/10 (B10) spleen cells and the immune spleen cells were fused with BALB/c myeloma cells (NS1). One of the monoclonal antibodies (H9/25 antibody) produced by the hybrid cells was studied. It reacts with subpopulations of B10 lymphocytes as well as some lymphoid tumor lines including some of the Abelson virus-induced leukemias. The antigen recognized by H9/25 antibody is expressed on lymphocytes from all the B10 congeneic mice tested as well as some other strains of mice. No linkage between genes coding for the antigen and H-2 loci was found as judged by its presence on cells of the B10 strains regardless of H-2 type and the distribution of the antigen on Bailey recombinant inbred mice. The antigen is expressed on subpopulations of lymph node cells, spleen cells, thymocytes and bone marrow cells. The strain distribution of the H9/25 antigen seems to be identical to that of Ly-6, Ly-8 and Ala-1 antigens. However, the tissue distribution of the antigen recognized by H9/25 antibody, while similar to these alloantigens, is unique and the antigen may be distinct from the other alloantigens.